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CERTIFICATION WORKGROUP

Engine Certification Recommendations Report

Northeast Advanced Vehicle Consortium

NAVC0599-AVP009903 September 15, 2000

U.S Department of Transportation

U.S Environmental Protection AgencyCalifornia Air Resources Board

by

Northeast Advanced Vehicle Consortium

112 South Street, Fourth Floor

Transient Operation Analysis By

West Virginia University

Department of Mechanical Engineering

Morgantown, WV

Copyright 2000, NAVC, DOT, All Rights Reserved

About AVP and NAVC

The NAVC Hybrid Transit Bus Certification Project was generously supported by the UnitedStates Department of Transportation’s Advanced Vehicle Technologies Program (AVP) TheAVP combines the best in transportation technologies and innovative program elements to

produce new vehicles, components, and infrastructure for medium- and heavy-duty transportationneeds The primary objectives of AVP are to:

• reduce vehicle emissions beyond 2004 standards,

• improve vehicle fuel efficiency by 50 percent,

• make the United States globally competitive in advanced vehicles, components andinfrastructure, and

• increase public acceptance of advanced transportation technology

The AVP program continues the approach developed by the Defense Advanced Research

Projects Agency (DARPA) Electric and Hybrid Vehicle (EHV) Technologies program of

forming partnerships with other federal agencies, private companies, research institutions andstate and local governments to expedite technology development vital to the nation’s interests

The Northeast Advanced Vehicle Consortium (NAVC) is a public-private partnership of

companies, public agencies, and university and federal laboratories working together to promoteadvanced vehicle technologies in the Northeast United States The NAVC Board of Directorsincludes a representative of the New England Governors’ Conference and the Northeast States forCoordinated Air Use Management and representatives appointed by the eight Northeast

governors and the mayor of New York City Its participants have initiated numerous projects,spanning a wide range of technology areas including electric, hybrid-electric and fuel cell

propulsion systems, electric and natural gas refueling, energy storage and management, andlightweight structural composites The NAVC receives funding from federal agencies and privatemembers

The Northeast Advanced Vehicle Consortium (NAVC) thanks the U.S Department of

Transportation (DOT) Advanced Vehicle Technologies Program for the funding and support ofthis project We recognize Shang Hsiung of DOT for his personal assistance The project wasinitiated by Sheila Lynch, NAVC Executive Director, and organized and lead by Thomas Webb,NAVC Project Director

The NAVC thanks M.J Bradley & Associates for their excellent work on the project, particularlyThomas Balon, the lead author; Paul Moynihan, MJB&A staff engineer; and Amy Stillings,MJB&A staff analyst

The NAVC thanks West Virginia University (WVU) for sharing and carrying forward the wealth

of knowledge they possess with regard to engine certification testing We personally thank Dr.Nigel Clark for his oversight and providing expertise on interactions between an engine’s

operating conditions and emissions and the rest of the WVU staff for their participation

In addition, the NAVC thanks the United States Environmental Protection Agency (EPA) andCalifornia Air Resources Board (CARB) for its participation In particular, we thank DennisJohnson (EPA), Tom Stricker (formerly EPA), Jack Kitowski (CARB), Tom Chang (CARB) andFernando Amador (CARB) for expressing a deep interest in the project from the beginning and adesire to explore alternate means to certify hybrid transit buses

The NAVC would also like to thank the electric drive manufacturers, specifically Allison

Transmission, Lockheed Martin Control Systems and ISE Research for allowing access to

proprietary data that is at the heart of this report In addition, the ongoing participation of otherinterested parties and all workgroup participants was extremely valuable, including hybrid

component suppliers, engine manufacturers, bus equipment manufacturers, environmental

organizations and other governmental agencies

Finally, the NAVC thanks the American Public Transportation Association for getting the hybridbus certification ball rolling several years ago Frank Cihak and Jerry Trotter provided valuableinsight and contacts

The viewpoints expressed in this report are those of the authors While the report was preparedand reviewed by a broadbased and representative group of people from industry and government(listed in Appendix A), none of the participating organizations were asked to, nor have theynecessarily, endorsed or adopted the findings and recommendations included in this report

regulators Historically, engines for heavy-duty transit buses have been certified using the federaltransient procedure (FTP), but engines that may be optimized for today’s series hybrid buses maynot be capable of following the behavior prescribed in the FTP cycle.

While chassis testing may ultimately resolve this dilemma, new rulemaking for certifying transitbus chassis (instead of engines) is a long way off A short-term, alternate engine certificationprocedure would help this viable, clean bus drive technology enter the market now Hybrid-electric transit bus engines have to meet the same emission standards as conventional urban busengines, however they should be tested on cycles that are representative of their actual operatingcharacteristics

The NAVC formed the Hybrid Transit Bus Certification Workgroup to help industry and

regulators elect an appropriate existing engine cycle as an alternate to the FTP cycle During thecourse of several well-attended meetings, the government-industry group exchanged the latestinformation on hybrid-electric drive bus technology and identified an approach to near-termhybrid bus engine certification The group collected and analyzed data from a representativesample of state-of-the-art series hybrid buses operating in normal revenue service in New York,Boston and Los Angeles The data represents three leading electric drive manufacturers active inthe market at this time

This report summarizes the analysis of in-use hybrid-electric bus engine data and compares it toconventional bus, marine and off-road engine test cycles The analysis indicates that the hybridengines have substantially less aggressive transient behavior than the FTP prescribes Sinceextreme transients cause the formation of particulate matter and carbon monoxide in dieselengines, and precipitate air/fuel ratio deviation in spark ignited engines, hybrid engine emissionsare better represented by steady state operation

A modal data analysis reveals that the Euro III 13-Mode Test Cycle is the most inclusive andrepresentative cycle for hybrid engines Furthermore, it is widely used by regulators and enginemanufactures, making it practical for implementation in the near term At this time, we

recommend the use of the Euro III to certify engines for use in series hybrid buses only

Additionally, we recommend a sunset date of 2004 to allow industry and regulators to reevaluatethe cycle in light of advancements in hybrid technology and engine emission controls Therecommended sunset date also coincides with the significantly reduced emission levels that will

a general in-use methodology for analyzing hybrid engine operation This chapter may be of usefor future test programs Chapter 5 provides the results of the analysis of three different hybridengines in use in New York, Boston and Los Angeles Chapter 6 draws conclusions and

recommends the Euro III test cycle for near term certification of engines for series hybrid transitbuses

1.2 Proven Hybrid Emissions Reductions

1.3 The Certification Challenge

1.4 The NAVC Hybrid Transit Bus Certification Workgroup

1.4.1 Special Test Procedures

2.0 Series Hybrid-Electric Buses

2.1 Hybrid-Electric Drive Definition

2.1.1 Drive System Design Variations

2.1.2 Engine Sizing

2.1.3 Batteries and Regenerative Braking

2.2 Engine Operation and Control

2.3 Emission Implications

3.0 Existing Engine Test Cycles

3.1 The FTP Transient Cycle

3.2 Steady-State Cycles

3.2.1 Generator Set Test Cycle

3.2.2 Off Road Equipment Test Cycle

3.2.3 Marine Engine Test Cycles

3.2.4 Other Steady-State Test Cycles

3.3 Conclusions

4.0 In-Use Data Collection

4.1 Data Collection Overview

4.2 Modal Data Analysis Methodology

4.3 Transient Data Analysis Methodology

4.4 Modal FTP Baseline

4.5 Conclusions

5.0 Manufacturers Data Analysis

5.1 NAVC Workgroup Data Collection

5.1.1 NAVC Workgroup Data Reduction

5.2 Engine Data—Transient Analysis

5.3 Engine Data—Modal Analysis

5.3.1 Modal Test Cycle Comparisons

5.4 Conclusions

6.0 Conclusions and Recommendations

6.1 Key Findings

6.2 Future Research Needs

Appendix A: Attendance List for NAVC Hybrid Transit Bus Certification Workgroup Meetings

List of Tables

Table 1.1: Results of NAVC Hybrid Testing Project

Table 1.2: Current Hybrid-Electric Engine and Turbine Applications

Table 1.3: Hybrid Bus Certification Pathways

Table 1.4: EPA Urban Bus Engine Standards

Table 1.5: CARB Urban Bus Diesel Engine Standards

Table 3.1: Steady State Test Cycles

Table 5.1: Commercially Available Hybrid Buses

Table 5.2: Hybrid Bus Specifications

List of Figures

Figure 1.1: U.S Hybrid Bus Market

Figure 1.2: Comparison of Tailpipe Emissions between a Conventional and Hybrid Diesel BusFigure 2.1: Vehicle Energy Requirements

Figure 3.1: The FTP Transient Cycle

Figure 3.2: Five-Mode Steady-State Test

Figure 3.3: Eight-Mode Steady-State Test

Figure 3.4: E4 and E5 Marine Cycles

Figure 3.5: Thirteen-Step Japanese Steady-State Test

Figure 3.6: Thirteen-Mode Euro III Test

Figure 4.1: FTP Load-Point Analysis

Figure 4.2: FTP Cycle Histogram

Figure 4.3: FTP Horsepower Variations

Figure 4.4: FTP Cycle Engine Torque Distributions

Figure 5.1: LMCS Bus #6352 In-Use Speed

Figure 5.2: Comparison of Speed Behavior on FTP Cycle and In-Use Hybrid Test Data

Figure 5.3: Comparison of Horsepower on FTP Cycle and In-Use Hybrid Test Data

Figure 5.4: Comparison of Torque on FTP Cycle and In-Use Hybrid Test Data

Figure 5.5: Combined Hybrid Engine Torque Speed Hp-Hr Weighted, 1% Intervals

Figure 5.6: Combined Hybrid Engine Torque Speed Hr-Hp Weighted, 10% Intervals

Figure 5.7: Combined Hybrid Engine Torque Speed Hp-Hr vs 8178 5-Mode

Figure 5.8: Combined Hybrid Engine Torque Speed Hp-Hr vs 8178 8-Mode

Figure 5.9: Combined Hybrid Engine Torque Speed Hp-Hr vs 8178 Marine E4 and E5

Figure 5.10: Combined Hybrid Engine Torque Speed Hp-Hr vs 13 Step Japanese

Figure 5.11: Combined Hybrid Engine Torque Speed Hp-Hr vs Euro III 13-Mode

Figure 6.1: Comparison of Horsepower on FTP Cycle and In-Use Hybrid Test Data

Figure 6.2: Combined Hybrid Engine Torque Speed Hp-Hr vs Euro III 13-Mode

1.0 Hybrid Bus Overview

Chapter 1 outlines the need for a special test procedure for certifying heavy-duty hybrid transitbuses in the United States It gives an overview of the Northeast Advanced Vehicle Consortium(NAVC) certification project including a brief status of the hybrid bus market, results of recentemission testing of hybrid buses, and explanation of the hybrid bus certification challenge Thehistory of the NAVC Hybrid Transit Bus Certification Workgroup is summarized, as well as thereason for recommending an alternate, existing engine cycle for near-term certification of enginesfor series hybrid transit buses

1.1 Introduction

The growing need to reduce fuel consumption and lower emissions in the United States

transportation sector has spurred urban transit bus operators to pioneer the adoption of alternatefuels and new drive system technologies One of the most promising technologies to receiveattention is hybrid-electric drive, which consists of two or more onboard fuels that supply energy

to electric traction motors that in turn drive the wheels By contrast, conventional drive employs

an internal combustion (IC) engine to generate rotational force that is then only mechanicallytransferred to drive the wheels

The electric drive improves drive system efficiency, reduces energy consumption, recoversenergy, reduces emissions, and improves driveability Pure battery-electric transit buses do notappear feasible in the near term because the power and energy requirements associated withtypical urban transit bus drive cycles exceed the performance (primarily range) capabilities ofcurrent battery technologies However, hybrid-electric drive, or electric drive that uses twosources of onboard motive energy (typically, an IC engine and traction battery), can easily meetand exceed the urban transit bus drive cycle requirements while still dramatically improving fueleconomy and emissions Thus, hybrids have emerged as a future direction for transit as well asother light and heavy-duty vehicles

Rapid technological progress has occurred in electric drive components and system integrationduring the last five years A growing number of companies are developing and beginning tosupply commercial hybrid-electric drive products to the truck and bus markets In 1998 the Orion

VI Hybrid bus became North America’s first commercial hybrid product offering from a majortransit bus manufacturer Other products are being tested and offered for sale by NovaBUS, New

Flyer, Advanced VehicleSystems and others Hybridbuses are being used inrevenue service in a number ofcities including Cedar Rapids,Chattanooga, Los Angeles,New York City, Tampa, andTempe

While the population of hybridbuses is relatively small today,the demand is growing, as seen

in Figure 1.1 In a studyrecently prepared by theNAVC for the Transportation

Source: NAVC, based on actual and planned purchases.

US Hybrid Bus Population

Research Board,1 the NAVC estimated there were about 70 hybrid buses delivered and another

230 or so on order in the United States as of December 1999 The potential exists for thousands

of hybrid transit bus orders over the next several years to meet customer demand for cost

effective pollution reduction strategies Hybrid-electric drive technology is particularly well

suited to meet this need in the near term

1.2 Proven Hybrid Emissions Reductions

Hybrids have been recently shown

to significantly lower overall

emissions and improve fuel

economy when compared to

conventional drive An in-depth

test program was performed in 1999

by the NAVC for the Defense

Advanced Research Projects

Agency (DARPA) to evaluate fuel

economy and emissions

performance of state-of-the-art

hybrid-electric buses as well as

conventional and alternatively

fueled mechanically driven transit

buses.2 Using the West Virginia

University (WVU) chassis

dynamometer, the NAVC tested six

heavy-duty hybrid transit buses on

multiple drive cycles, measuring emissions and fuel economy The particulate matter (PM)

results for the diesel-electric hybrids were 50 percent lower than for a conventional art mechanically driven diesel bus,3 and oxides of nitrogen (NOx) emissions were 30-40 percentlower The hybrids exhibited the lowest carbon monoxide (CO) emissions of any bus tested (up

state-of-the-to 70 percent lower), and the hybrids demonstrated significantly lower state-of-the-total greenhouse gas

emissions than either conventional diesel or compressed natural gas (CNG) buses Table 1.1

shows the results of the NAVC hybrid vehicle emissions chassis-based test results.4

1

“Hybrid-Electric Transit Buses: Status, Issues and Benefits,” Transportation Research Board (TCRP

Report 59), National Academy Press, 2000, is available at www.nationalacadamies.org/trb/bookstore

4

NovaBUS completed emissions testing of its RTS model hybrid transit bus at Environment Canada onMay 26, 2000 The bus was equipped with the LMCS hybrid system and was tested at 34,500 lb on D1fuel The bus was equipped with a particulate filter designed to suppress sulfate production Emissionresults on the CBD-14 driving cycle were: CO = 0.0 g/mi; NOx = 14.54 g/mi; THC = 0.07 g/mi, PM =0.0048 g/mi; CO2 = 2304 g/mi and fuel economy of 4.40 mpg

Source: NAVC, MJB&A and WVU, 2000.

Figure 1.2: Comparison of Tailpipe Emissions between a Conventional and Hybrid Diesel Bus

PM10

0.24

0.12

0 0.05 0.1 0.15 0.2 0.25 0.3

NovaBUS RTS (DDC50)

NovaBUS RTS (DDC50)

Orion Hybrid

VI (DDC30)

D1 fuel used in both buses DDC50 certified to PM 0.05g/bhp-hr DDC30 certified to

PM 0.10g/ bhp -hr equipped with a particulate filter trap.

The reasons for the reductions are severalfold Regenerative braking contributes significantly toreducing fuel consumption and thereby improving efficiency Regenerative braking takes

advantage of the energy storage system to capture the kinetic energy of the vehicle during

braking This is accomplished by using the drive motors as generators during braking to

recapture the vehicle’s kinetic energy and restore a portion of this energy back to the energy

storage device to be used later, for example during acceleration

Another contributing factor to the reductions is the fact that, on a series hybrid, the engine is notdirectly coupled to the vehicle drivetrain (i.e., the electric drive motor alone drives the wheels)

This allows the auxiliary power unit (APU) to operate independently from the vehicle This

would theoretically allow the engine/generator to operate at peak efficiency and optimized

emission load points Series hybrid control strategies typically prevent the engine from operating

in zones where its efficiency may be low and its emissions high

Reduced air pollutant emissions from hybrid-electric vehicles is an important consideration for

transit agencies, especially those in congested urban areas The emission reduction of hybrids isdirectly tied to reduced fuel consumption; when less fuel is used, fewer emissions are produced

In addition, when an engine in a conventional vehicle is under heavy load, such as acceleration, itoperates in areas of the engine map that are more heavily emissive By supplementing the enginewith electric drive motors as the hybrid does, and operating the engine in a narrow zone, heavy-load operation may be avoided altogether resulting in lower emissions

1.3 The Certification Challenge

Industry and regulators have recognized for some time the unique challenge posed by hybrids inthe emissions certification process compared to traditional transit buses Current series hybrid

transit buses often use new or unconventional engine technology that is smaller and different in

design, control and operation from conventional engines Table 1.2 shows the variety of enginesand turbines used in hybrid vehicles today Some of the hybrid engines in use today do not meetcurrent EPA urban bus standards on the FTP cycle, however many demonstrate superior

emissions performance in chassis testing of hybrid buses (see Figure 1.2) As the technology

evolves, system designers will want to develop hybrid engine and system controls to achieve

further emissions reductions and fuel economy improvements All of these factors make

certification of hybrid engines a challenge

Table 1.1: Results of NAVC Hybrid Testing Project

Orion-LMCS VI Hybrid Diesel 0.1 19.2 0.08 0.12 2,262 0.0 4.3 Orion-LMCS VI Hybrid Diesel (no regen.) 0.04 22.0 0.12 0.24 2,625 0.0 3.7 Orion-LMCS VI Hybrid MossGas 0.1 18.5 0.03 0.02 2,218 0.0 4.2 Nova-Allison RTS Hybrid LS Diesel 0.4 27.7 bdl* bdl* 2,472 0.0 3.9 Nova-Allison RTS Hybrid LS Diesel (no regen.) 1.0 32.1 0.03 0.07 3,010 0.0 3.1 NovaBUS RTS Diesel Series 50 3.0 30.1 0.14 0.24 2,779 0.0 3.5 NovaBUS RTS MossGas Series 50 1.0 32.2 0.05 0.09 2,816 0.0 3.3 Neoplan AN440T CNG L10 280G 0.6 25.0 0.60 0.02 2,392 14.6 3.1 New Flyer C40LF CNG Series 50G 12.7 14.9 3.15 0.02 2,343 17.4 3.1 Orion V CNG Series 50G 10.8 9.7 2.36 0.02 2,785 23.7 2.6

* bdl = below detectable limit

Source: NAVC, MJB&A and WVU, 2000.

The Engine Compliance Program at the Environmental Protection Agency’s (EPA’s) Office ofTransportation and Air Quality is responsible for certifying engines for heavy-duty practices TheCalifornia Air Resources Board (CARB) Mobile Sources Control Division performs a similarfunction for certification in the state of California Both EPA and CARB use the same testprocedures for urban bus engine certification.

Emission certification of trucks and buses is presently done using the engine only Chassis basedemissions testing in the United States only occurs on light duty vehicles and light duty trucks,except in California where chassis based certification of medium-duty vehicles is allowed In aconventional mechanically driven vehicle, the engine performs the work and its speed and torquevaries according to the demands of the transient drive cycle The Federal Code of Regulations(40 CFR Part 86, subparts I and N) prescribes an engine dynamometer test for heavy-duty

certification In California, the comparable regulation can be found in Title 13, California Code

of Regulations, Section 1956.1 Specific lab equipment and test protocols are also described.Engines are certified on the Federal Test Procedure (FTP) transient cycle Emissions are

measured and reported in units of grams of emissions per brake horsepower hour (g/bhp-hr)delivered by the engine under specific load regimes The emissions are not allowed to exceedcertain standards set by EPA and California Engine manufacturers are responsible for complyingwith exhaust emission standards

Hybrid engines can meet the urban bus PM standard on the FTP with additional modifications asdemonstrated by the 2000 model year DDC S30 engine However, research and development ofhybrid engines in the near future may result in engine optimizations for specific operating ranges,which may be prohibited by current FTP certification protocol Pursuing special test procedureoptions or developing a hybrid-specific engine test protocol would allow the engine optimization

to be realized during the certification procedure resulting in lower engine emissions

The challenge is for industry and regulators to find an acceptable cycle on which to test hybridengines for purposes of emissions certification If the FTP transient cycle alone is used willhybrid engines be able to meet the urban bus standard and at what cost? Will viable enginetechnologies be excluded if the FTP is used? Will the FTP allow flexibility to improve andoptimize hybrid engine controls for further emission reductions in the future? Is there anotherengine cycle that would better represent hybrid engine operation that could be used for

certification purposes? These questions were being debated in the hybrid industry when theNAVC formed the Hybrid Transit Bus Certification Workgroup

Table 1.2: Current Hybrid-Electric Engine and Turbine Applications

Engine Manufacturer / Model

1 – Compression Ignition (CI), Direct Injection (DI), Spark Ignition (SI)

2 – In process of certifying to EPA Urban Bus PM standard of 0.05 g/bhp-hr on the FTP

1.4 The NAVC Hybrid Transit Bus Certification Workgroup

The primary goal of the NAVC Hybrid Transit Bus Certification project was to develop a

comprehensive protocol for the testing and certification of heavy-duty hybrid-electric vehicles

To this end, the NAVC put together the Hybrid Transit Bus Certification Workgroup of

government and industry stakeholders to determine the best course of action The project wascoordinated by the NAVC and supported by the Advanced Vehicle Program under the

administration of the United States Department of Transportation

The NAVC hosted two meetings of the Workgroup in the spring of 2000 A variety of

presentations were given at each meeting to share the latest emissions and fuel economy data withall participants and to explore certification concepts The meetings drew a large and

representative body of participants from all aspects of the industry including manufacturers ofengine and gas turbines, aftertreatment, hybrid drive systems and bus equipment, as well astransit operators, the American Public Transportation Association, EPA, state representatives,other environmental advocacy groups and industry consultants A complete list of participantsappears in Appendix A The Workgroup objectives were to balance industry and governmentinterests, provide current and unbiased information pertinent to hybrid certification, explore thefeasibility of alternate means to certification, validate those means, and publish and distribute itsrecommendations widely

At its first meeting, theWorkgroup identifiedthree pathways tohybrid bus certification(see Table 1.3) Thefirst (immediate)pathway represents thestatus quo Engines forhybrid bus orders placedthrough 2000 will mostlikely be certified on thecurrent federal transient cycle The second (short-term) pathway is to certify using an existing,alternate cycle that better represents in-use hybrid engine operation The Workgroup decided itsresources were best spent on selecting and justifying the alternate, existing cycle The third (longterm) pathway is to develop new, hybrid-special test cycles for engines and/or chassis.5 Thispathway is considered long term because it requires rulemaking that is expected to take severalyears from start to finish The third pathway is beyond the present scope of the NAVC

6

The newly formed Society of Automotive Engineers (SAE) Truck and Bus Hybrid and Electric VehicleCommittee is working to identify the appropriate standards for electric and hybrid-electric trucks and busesincluding modification of existing standards or development of new ones, as required The NAVC

Workgroup is preparing to work in partnership with the SAE to revise SAE J1711, the recommendedpractice for measuring emissions and fuel economy of light-duty hybrid-electric vehicles using a chassisdynamometer

Table 1.3: Hybrid Bus Certification Pathways

Certify on the

current FTP

Other optionswithin the currentregulatorystructure (i.e.,special testprocedures)

Rulemaking forhybrid technology(possibly toinclude chassis-based certification)

The general consensus

among participants in the

Workgroup was that

short-term certification

testing to help early

market penetration should

remain engine based and

the responsibility of the

engine manufacturers A

sunset date of 2004 was

selected due to new

emissions standards that

go into effect, and the

need to re-evaluate the

conventional/advancedtechnology path standards,which diesel-hybrid buseswould follow

To help build consensus forshort term hybrid enginecertification, the NAVCWorkgroup turned to theSpecial Test Proceduresprovisions in the code ofregulations for Federal andCalifornia certification

1.4.1 Special Test Procedures

The Administrator may, on the basis of written application by a manufacturer,

prescribe test procedures, other than those set forth in this part, for any

light-duty vehicle, light-light-duty truck, heavy-light-duty engine, or heavy-light-duty vehicle which the

Administrator determines is not susceptible to satisfactory testing by the

procedures set forth in this part - 40 CFR 86.090-27

Engine Emission Standards (g/bhp-hr)

**Proposed, with fuel sulfur limitations and a NOx/NMHC phase-in

Source: U.S EPA.

Table 1.4: EPA Urban Bus Engine Standards

Engine Emission Standards (g/bhp-hr)

* Nominal NOx level based on emission standards of 2.4 g/bhp-hr

NOx plus non-methane hydrocarbons (NMHC) or 2.5 g/bhp-hr plus

In January of 1998, EPA granted permission to Navistar to use a special test procedure in

certifying the T444E engine, which had been designed for light heavy-duty market, for use in alimited number of heavy-heavy duty hybrid transit buses In its request to EPA, Navistar arguedthat the quasi-steady state D-2 cycle was more representative of actual engine operation in thehybrid bus than the transient FTP cycle Furthermore, Navistar showed that the engine couldmeet the urban bus emission standards on the D-2 cycle EPA approved Navistar’s request to usethe D-2 cycle and on-highway deterioration factors, but limited it to one model year only andrequired the engine be properly labeled for hybrid use only

EPA also requested that Navistar share in-use hybrid engine operation and chassis data with EPA

in the future to help it better understand the benefits of the hybrid engine and to determine thesuitableness of the alternate cycle used for certification The 2000 NAVC hybrid emissions study(see section 1.2) reported the results of a side-by-side chassis comparison of hybrid to

conventional drive technology to help address regulators’ concerns The NAVC Hybrid TransitBus Certification Workgroup set out to analyze in-use hybrid engine data in order to determinethe most representative, existing engine cycle for certifying hybrid engines While it does notappear that the D-2 cycle is representative of the hybrid application, the use of a steady state cycleappears acceptable

2.0 Series Hybrid-Electric Buses

Series hybrid-electric vehicles are an outgrowth of pure electric vehicles, combining the

developments in electric drive systems and energy storage devices with conventional technology

to produce the next generation of vehicles with low emissions and high fuel economy, whilemaintaining good performance attributes This chapter begins by defining what a hybrid-electricdrive system is, describes some design variations, and explains how hybrids differ from

conventional vehicles We discuss the major design areas that affect hybrid engine operation andemissions, including overall system design, engine type and size, engine controls, and

regenerative braking These factors help explain why hybrid bus engine emissions do not

correlate to hybrid bus chassis emissions In particular, the engine in a hybrid was hypothesized

to operate in more of a steady state than transient mode, which could provide a key to enginecertification procedures

2.1 Hybrid-Electric Drive Definition

A hybrid-electric vehicle is one that has two motive power sources used either separately or incombination These two sources are the electrical energy storage device such as a battery pack,supercapacitor or flywheel, and the auxiliary power unit (APU), such as an internal combustionengine, turbine or fuel cell Hybrid-electric vehicles also contain a single or multiple electricmotors that provide power to the wheels Power to the motors is provided by either the energystorage device or the APU, or in combination, depending upon the type of hybrid-electric vehicle.Hybrid-electric vehicles use the signal from the accelerator pedal to determine how much powerwill be provided by the APU and/or by the energy storage device The vehicle’s computerconstantly monitors the battery state-of-charge (SOC) to determine if engine operation is needed

to recharge the batteries, independent of the driver signals Because the bus does not rely on theengine for its peak power output at the axles, the hybrid bus engine is sized based on a

combination of the average bus power demand and the peak power demand, rather than the peakpower demand alone For the same power output, a smaller engine operated at high percentageoutput will usually be more efficient than a larger engine operated at lower percentage output,because the frictional and pumping losses of the smaller engine are lessened In this way, theengine in a hybrid vehicle can offer greater cycle average fuel efficiency, and hence can also offerthe potential to lower emissions

2.1.1 Drive System Design Variations

There are several different kinds of hybrid-electric vehicles, which are categorized as series,parallel or dual mode, engine or battery dominant, charge sustaining or charge depleting

Currently charge-sustaining series and parallel hybrids have received the most attention Theexception is the turbine hybrid built by Advanced Vehicle Systems and Capstone Turbine, which

is a battery dominant, charge depleting series hybrid with a micro-turbine as the APU

In a series hybrid all of the power necessary to drive the wheels is provided by electric drivemotors or in other words, the engine is mechanically de-coupled from the wheels This

configuration consists of an APU that is used to charge the batteries or provide electric powerdirectly to the drive motors In this case, the APU does not necessarily operate in a load-

following manner and is basically independent so that the engine can be optimized to run in anarrow range of operating conditions, in a zone of both high efficiency and low emissions.Optimizing the engine to operate within a narrow band is achieved partially through enginemanagement software that prohibits it from moving out of the desired zone and partially by theoriginal design specifications of the attached generator

In a parallel hybrid, both the engine and the drive motors provide power to the wheels Ratherthan having to cycle the energy from the engine through a generator and then to the drive motors,the mechanical energy from the engine can be applied through a differential directly to the drivewheels In stop-and-go applications, the engine is more load following than in a series hybrid and

is better suited to continuous operation at higher speeds (i.e., the engine and transmission

combination are speed following) If the application is known, the engine in a parallel hybrid can

be partially optimized for efficiency and emissions within a specific zone of operation

Compared to a conventional bus, series and parallel hybrids offer the advantage of reducing theamount of energy provided to the wheels by the engine By supplementing engine energy withenergy from the batteries, the engine will be less load-following than in a conventional bus, andwill therefore use less fuel Reducing the amount of fuel correlates directly to reduced emissions.Also, since the engine is less load-following and does not necessarily require operation nearmaximum power, a smaller engine can be utilized

2.1.2 Engine Sizing

Hybrid engine sizing is affected by the size of the energy storage device, which contributes towhether or not it will be of battery or engine dominant design There is no clear-cut definition ofbattery vs engine dominance and in fact many of the current hybrid offerings are right in themiddle with a moderately sized battery pack and engine With a smaller engine the hybrid canstill meet the acceleration demands with help from the batteries but with reduced fuel

consumption and reduced emissions

Generally speaking, the determination of battery or engine dominance is actually better madeusing the terms charge sustaining vs charge depleting as these terms are easier to define A pureelectric bus is obviously both charge depleting and battery dominant as it derives all of its motiveenergy from the batteries Several prototype fuel cell buses have been developed as “hybrid-electric” but some of these buses do not have any batteries at all, much like an electric trolley, andtherefore cannot recover energy during braking The best example of an engine dominant hybridwould be a vehicle that adds the ability to capture regenerative braking energy but has little if anypure electric range such as the Honda Insight Electric vehicles with range extending APUs such

as the AVS Capstone turbine hybrid are considered battery dominant On the other end of thespectrum is the Toyota Prius that utilizes batteries for load leveling, regenerative braking andsome minimal level of electric only range Most of the hybrid-electric transit buses on the streettoday are charge sustaining and are considered engine dominant even though they possess anelectric range of nearly 10 miles, quite a distance for a 40-foot transit bus

An advantage to an engine-dominant hybrid is that the APU provides most of the energy

immediately to the drive motors thus eliminating the energy losses inherent in the energy storagesystem In a battery-dominant hybrid, just the opposite occurs, and the drive motors get most ofthe energy from the energy storage system The advantage of this system is that load following isminimized for the engine, allowing the zone of torque and speed operation of the engine to bemore closely defined

The issue of engine dominance vs battery dominance in the emission testing sense is importantbecause charge sustaining, engine dominant hybrid-electric vehicles derive all of their powerfrom the onboard APU while battery dominant vehicles derive most of their power from theutility grid

A dual mode hybrid (Toyota Prius) is designed so that it embodies both series and parallel hybridoperation characteristics The engine and two motor/generators are integrated with a geartrain toform a sophisticated continuously variable transmission This is a more complex type of hybrid

in terms of design and management As with series and parallel hybrids, the dual-mode hybrid

can be either engine or battery dominant Currently there are no transit buses of this design inservice in the United States.

2.1.3 Batteries and Regenerative Braking

Regenerative braking allows the kinetic acceleration energy to be recovered to recharge thebatteries during vehicle deceleration During acceleration, a certain amount of energy is required

to bring the vehicle mass up to speed However, when a vehicle equipped with a conventionalbus comes to a stop, that energy is dissipated through the service brakes as heat, essentiallywasted energy When a hybrid bus decelerates, the drive motor torque is reversed and the

resistance of an electromagnetic field creates electrical energy that is cycled back to recharge thebatteries During peak demands some power is provided by energy stored during regeneration, sothat the demand on the engine is lessened This reduces fuel consumption and emissions Also,when power is demanded rapidly, the hybrid system need not demand instantaneous high poweroutput from the engine, but may instead raise engine power slowly, relying on power available inthe batteries for good vehicle pedal response The reduction of instantaneous demand on theengine, or “smoothing”, can have a strong effect in reducing diesel engine PM production

Not all of a vehicle’s kinetic energy can be captured by the batteries, however Generally

speaking, a vehicle can and usually does stop much more quickly than it can accelerate and thehybrid-electric energy storage system has limited ability to accept the energy quickly This isbecause acceleration is limited by the power available from the drive system while braking islimited by the traction of the

tires Figure 2.1 shows a

representation of the energy

required for a vehicle to

accelerate to a set speed and

cruise, and finally brake to a

stop This illustration, taken

from a single cycle element

of the Central Business

District chassis testing cycle,

shows that the deceleration

takes place about twice as

fast as the acceleration

During rapid deceleration

like this, the ability to

recover the kinetic energy

through the regenerative

braking system is limited by

the amount of energy the drive system (drive motor, controller, and batteries) can accept Usuallythe system and battery pack are designed for the peak power demand during acceleration If thebattery pack cannot accept all the energy during deceleration, the service brakes are engaged.The energy is dissipated as heat Devices such as ultracapacitors, that can accept high chargerates, are likely to emerge as an energy-saving feature in future hybrid designs

Hybrid brake system configuration also affects regenerative braking system efficiency Sinceregenerative braking uses the drive motors in reverse, and most current hybrid-electric designs arerear wheel drive, the braking energy that passes through the rear wheels is all that can be

captured A significant portion of braking for any vehicle occurs at the front brakes and the onlyway to capture this braking energy is to put drive motors on the front wheels as well (or brakeentirely with the rear wheels, which may result in unsafe handling) Other losses occur in the

Figure 2.1: Vehicle Energy Requirements

-300 -200 -100 0 100 200 300

-5 0 5 10 15 20 25

batteries and other components of the electrical systems as well as the mechanical losses

including the differential

2.2 Engine Operation and Control

A typical diesel internal combustion engine is a mechanical power device that converts chemicalheat and expansion energy into mechanical rotational energy via a crankshaft In a conventionalvehicle this rotational power is directed to the vehicle wheels via a transmission and a differential

so that the proper wheel speeds can be obtained The transmission and differential are gearedsuch that at low vehicle speeds the system has a significant amount of torque multiplication (asmuch as 100x) As vehicle speeds increase the transmission is shifted up (to a lower numericalgear ratio) resulting in lower torque multiplication such that in final drive the vehicle engine isoperating at about three to twelve times wheel speed depending upon vehicle design parameters.The important point in conventional mechanical drive is that the engine is connected to thewheels of the vehicle so that engine speed is dependent upon vehicle speed under constrainedtransmission conditions The highway portion of the FTP cycle consists of significant engineoperation at high speed while load varies typical of a vehicle operating essentially in top gear andcruising at highway speeds Also, the FTP embodies the “gear-bound” technology typical of the1970s The varying engine load is then induced by hills such that engine load increases butengine speed tracks with the relatively constant speed of the vehicle The end result of this type

of vehicle configuration is that the engine can operate over nearly all of its operating range forboth speed and torque Engine operation is generally vehicle dependent as well as duty cycledependent (see Chapter 3 for a discussion of duty cycles)

A series hybrid-electric vehicle essentially consists of an electric vehicle where all of the power isprovided to the wheels by the electric drive motors and power can be derived exclusively fromthe batteries if necessary In a hybrid vehicle, the engine is used to generate electrical powerfrom a liquid or gaseous fuel that is stored on board the vehicle While the APU may consist of afuel cell, which produces electric power directly, most of the hybrid vehicles today have either aturbine or a piston engine, which is producing rotational mechanical power To generate

electricity the engine or turbine is connected to a generator Because the main electric system in ahybrid-electric vehicle is isolated, the frequency of the power (60 cycles for ground power) doesnot apply

There are several benefits to a series hybrid-electric layout that are a direct result of having theengine de-coupled from the wheels The generator can be sized so that the engine is never

required to produce maximum torque and as a result avoids the typical engine operating zonewith relatively high particulate emissions, but still maintains the ability to vary speed Even in aload following application the engine responds to vehicle power demands instead of only torquedemands as in a conventional vehicle

Compare a series hybrid-electric vehicle in which all power must be provided by the APU to aconventional vehicle on the Central Business District chassis testing cycle During accelerationthe conventional vehicle’s engine speed increases at near maximum torque and then shifts gears.Engine speed again increases at maximum torque until 20 mph is achieved At 20 mph the enginespeed tracks vehicle speed (based on the overall gear ratio of the vehicle) and engine torque falls

to a relatively small value necessary to overcome road load In the hybrid-electric vehicle thetotal available power from the drive motors limits the demand for acceleration Because theengine in not connected to the wheels, the engine can ramp up to the engine speed necessary toproduce that power and stay there The end result is that while the engine in a hybrid-electricvehicle varies over a substantial speed range, the torque for each speed is relatively constant and

is below maximum available engine torque thereby allowing the engine to ramp up evenly while

minimizing PM emissions In addition to avoiding the high PM zone (upper left and centerquadrants) of the torque speed map, hybrid-electric APUs avoid much of the upper right andlower right quadrants of high NOx emissions and low engine efficiency The lower right region(high engine speed low torque) of low engine efficiency is avoided as it is physically impossiblefor the engine to operate there because it is coupled to a generator and control system that willcause the engine speed to decrease with reduced power output.

By de-coupling the engine from the vehicle wheels, and using the batteries to provide

supplemental power, you now have the ability to level the electrical demand from the APU(referred to as load leveling) That is during relatively short high power accelerations the APU isassisted by the vehicle’s batteries in supplying power to the drive motors Much of this

supplemental energy provided by the batteries will be recovered via regenerative braking whenthe vehicle comes to a stop As a result of this load leveling, the only time the engine in a hybridelectric vehicle would venture into the high speed, high torque, maximum power upper rightquadrant of the torque speed map would be during extended hill climbing or battery pack failure.The end result is an engine that in theory operates in a defined operating range with reducedtransient speed and torque changes

The overall efficiency of a hybrid drive system is determined by a combination of factors not theleast of which is the efficiency of the engine itself While steady state engine operation mayallow the engine to be tuned for peak efficiency, much of this energy will have to pass throughthe batteries, which are only about 80 percent efficient APU load following is generally used toavoid the inefficiency of the batteries as long as the engine and generator efficiency for its

operating range is within 20 percent of optimum Other reasons include wanting to preserve thelife of the batteries or maximizing regenerative braking energy recovery by removing the flow ofenergy to the batteries from the APU during braking

The engine in the hybrid-electric vehicle should in practice be far more steady state than a

conventional vehicle because the engine operating points are generally closer together and over asmaller range

2.3 Emission Implications

By using a smaller engine in a hybrid-electric vehicle and by electronically controlling the engineoperating points, emission savings are realized Assuming a diesel powered hybrid-electricvehicle, the issues surrounding minimizing hydrocarbon (HC) and carbon monoxide (CO)

emissions are essentially taken care of due to the fact that already low HC and CO emissions arefurther reduced by using add-on controls such as an oxidizing catalyst The real tradeoff inoptimizing an engine is between NOx and PM emissions

Presently the challenge in designing and calibrating diesel engines lies in simultaneously meeting

PM and NOx requirements A modern diesel engine, if optimized solely for efficiency, will yieldabout 15 to 20 grams of NOx per indicated horsepower-hour of work This happens over a broadrange of speeds and loads where the indicated power represents work done at the piston, andincludes both the brake (output) power and the friction losses in the engine This yield is

consistent because NOx formation requires both the presence of high temperatures and oxygen,and these are both available in the high temperature zones during the heterogeneous combustion

in the cylinder Production of PM is more closely allied to the air to fuel ratio in the engine.Diesel engines, unless far over-fueled, operate in a lean condition and are generally un-throttledwith only the fuel flow varying Although some PM may arise from unburned fuel at very lightloads, steady state PM generally increases exponentially with load, and it is a smoke limit (andhence fuel limit) that determines the maximum rated power of most engines (PM is therefore

readily reduced by de-rating the engine) Over the last decade PM has also been reduced throughmuch improved injection system design and improved in-cylinder charge motion.

NOx emissions have historically been reduced by retarding the injection of the fuel with respect

to the piston phasing In this way, tailpipe NOx emissions levels can be reduced by a factor of up

to three before the loss of engine efficiency due to late injection becomes unacceptable and beforethermal management of engine components becomes problematic Unfortunately, retarded timingcauses high PM production because there is less time for the fuel to burn and because the averagetemperatures during combustion are lower The timing issue is therefore often termed a “NOx -

PM tradeoff” Present day engines operate with retarded timing for NOx, and high air to fuelratios with high-pressure injection to reduce PM

In calibrating an electronically controlled engine, the manufacturer has the ability to configureinjection timing at any operating point independently of the timing at other points, which was notthe case with earlier mechanical injection and which was not traditionally anticipated by federalregulations Faced with the objective of meeting an emissions certification standard while

meeting the need for good fuel efficiency, it is likely that the calibration engineer will favorretarded timing to reduce NOx in those areas most heavily visited by the certification test It istherefore essential from a regulatory perspective that the certification represents sufficiently wellthe real in-use speed and torque ranges of the engine, else emissions inventory will become de-coupled from regulation It is for this reason that the present document seeks to identify the realworld operating zones of hybrid vehicle engines

Internal combustion engines as well as turbines are limited in power by the amount of combustionair they can aspirate In most cases more than enough fuel can be supplied if necessary

Assuming that the spray and duration characteristics of diesel fuel injection are respectable theformation of particulate will be minimized, as long as there is sufficient excess air In a dieselengine sufficient excess air is far lean of stoichiometric as are heavy-duty natural gas engines.Light duty CNG, propane and gasoline engines are typically stoichiometric allowing the use ofthree way catalysts for control of NOx The amount of air moving through an internal

combustion engine depends upon its displacement, speed (rpm) and whether it is fitted with aturbocharger At low engine speed (idle for instance) very little air flowrate is available to theengine and as a result power output is low as well As engine speed increases more combustionair is available and more fuel can be injected increasing engine power If minimal additional fuel

is injected engine rpm will increase moderately with minimal PM emissions Generally speaking,faster rates of change in engine speed require that larger amounts of fuel be injected during thetransient phase, which may result in excess PM emissions As a result, rapid changes in enginespeed at high load would likely result in a PM event while a rapid change in engine rpm at

relatively light load (revving the engine in neutral) would not result in a PM event

Transient operation of a turbocharged diesel involves even more subtle fueling management Thefollowing simplistic argument illustrates the issue At the one extreme, if a sudden demand forhigh power is met simply by allowing full fueling, that power demand is met quickly However,the turbocharger still takes finite time (several seconds) to achieve operating speed and relies onthe increased exhaust flow from the added fueling to achieve this speed During this finite timethe engine would be heavily fueled but would not have full airflow, and black smoking wouldresult

At the other extreme, the transient could be followed in a quasi steady-state fashion At thedemand for high power, an incrementally small additional quantity of fuel could be added, andthe turbocharger speed would rise incrementally, increasing the airflow incrementally, and

allowing another increment of fuel to be added If these increments are sufficiently small, no

additional PM would arise in the transient, but response time of increased power would be

unacceptably slow Present day transient management strategies lie between these two extremes.Since series hybrid vehicles do not require rapid power deployment from the engine, a far lessaggressive transient strategy can be adopted, and the production of additional PM above andbeyond the steady state level can be significantly reduced The end result is that a large portion

of the PM emissions from diesel engines happens as a result of transient engine operation both inspeed and power This is borne out in emission test information where PM emission rates for adiesel engine on the FTP exhibit roughly twice the PM emissions of the same engine on the EuroIII steady-state test cycle

We believe there is sufficient evidence that NOx emissions are primarily a result of peak

combustion temperatures and residence time and that the engine is generally unaffected bytransient vs steady state operation The similarity in NOx emission rates of engines on both theFTP and the Euro III 13 mode test indicates that engine manufacturers are largely able to tuneNOx emissions to the required standard and that NOx emissions are largely similar at all but peakpower load points Even though the operating points of the FTP and the Euro III tests are

substantially different the emission rates for these tests are similar

In summary, hybrid powertrains can offer lower emissions than conventional powertrains for thefollowing reasons:

• The recapture of energy during regenerative braking means that the cycle-averagedpower demand on the engine is reduced, leading to lower fuel usage and hence loweremissions

• The availability of electrical power from the batteries to satisfy rapid transient powerdemands means that sudden power demands on the engine are less necessary Thereduction in engine transient severity (“smoothing”) leads to lower PM and CO

3.0 Existing Engine Test Cycles

As reported in Chapter 1, the NAVC Hybrid Transit Bus Certification Workgroup chose to

pursue a near-term solution for certifying hybrid buses using an engine rather than vehicle test

In choosing an appropriate, alternate engine test cycle, the Workgroup reviewed the existing FTPtransient cycle test currently used to certify bus engines as well as a number of existing steady-state engine cycles that might match well to in-use hybrid engine operation Chapter 3 describesthe salient features of each of the transient and steady-state cycles These cycles are then

compared to actual hybrid bus engine operation in Chapter 4

3.1 The FTP Transient

Cycle

Typically, engines for heavy

transit buses are certified on

the FTP transient test cycle

The FTP transient cycle

consists of four phases that

mimic different types of

driving conditions from the

CAPE-21 database that was

derived from a variety of

heavy-duty vehicles operating

in Los Angeles and New York

during the early 1970s Figure

3.1 shows the FTP transient

cycle varies both engine speed

and torque over the course of

the test These conditions are

simulated to consider traffic in and around cities on both surface roads and highways The firstportion of the cycle is a New York Non Freeway (NYNF) phase that is meant to represent lighturban traffic volume but with frequent starts and stops The second phase, the Los Angeles NonFreeway (LANF), is meant to represent high volume, relatively free-flowing urban traffic (i.e.,few starts and stops) The third segment is the Los Angeles Freeway (LAFY) portion which ismeant to represent crowded highway traffic The final phase is a repetition of the NYNF

segment The FTP transient cycle can generally be described as a cold start test followed by a hotstart test A cold start is classified as starting the engine and test cycle after the engine has satovernight and has cooled down to cell temperature Overall, the FTP transient cycle consists of awide variety of speeds to simulate operating the engine in a vehicle on several different kinds ofduty cycles, and also frequently varies the engine load to provide for few instances of stabilized,sustained operating conditions

Although the FTP target torques may suggest high motoring efforts, diesel engines offer littlemotoring resistance and are simply operated in “closed rack” at maximum possible negativetorque during these sections of the FTP Such operation is permitted in the subsequent test

“engine braking” The original reason for not including negative torque in the report figures is that no work

Figure 3.1: The FTP Transient Cycle

FTP Engine Speed and Torque

-120 -80 -40 0 40 80 120

Time (Seconds)

-40 0 40 80 120 160 200 240 280

The FTP transient test cycle evaluates emissions on a gram per horsepower output basis, but thecycle itself is a percent torque speed trace with operating points defined in 1 second increments (1Hz) This allows engines of varying power levels to be evaluated on the same emission testcycle The FTP has only three field variables (time, engine speed and torque) with time in 1second intervals, speed as a percentage of operating range and torque as a percentage of ratedtorque at the defined speed Torque ranges from 0% to 100% for each available speed with 0%torque representing 0 net torque (sans internal losses) and 100% torque representing the peakavailable torque for that engine speed FTP percent speed is a little more complicated as 0%speed is defined as engine idle while 100% speed is defined as rated speed So if idle is 600 rpmand rated speed is 3000 rpm then 50% speed is 1800

rpm

3.2 Steady-State Cycles

Since an engine in a series hybrid-electric vehicle

operates more steady state than transient, the second

option for the Workgroup was to look at existing

steady-state engine test cycles The test cycles

examined include the Eight Mode, Five Mode,

Thirteen-Step Japanese, the Euro III Thirteen-Mode,

and the E4 and E5 Five-Mode Marine cycles, as

listed in Table 3.1 Each of these cycles was

developed independently and for different types of

engine certification purposes Modal test cycles,

such as the Five, Eight and Thirteen mode tests, are

defined as a weighted average of operation at

several operating load points based on the level of

emissions (grams) per amount of power produced

(hp-hr) such that the efficiency of the engine is

taken into account in establishing the emission

factors

3.2.1 Generator Set Test Cycle

The Five-Mode test, an International Organization of Standardization (ISO) test cycle, is designedfor testing of engines that function as a constant speed stationary generator set (genset)

application Since a genset is a constant generator speed application (i.e., engine rpm neverchanges), the Five-Mode test operates at 100 percent speed over five separate percent torqueratings, as seen in Figure 3.2 One thing to keep in mind is that the test cycle does not allow for

an engine to be rated at one speed and hooked up to a generator at a lower speed

is performed during these events by the engine and few emissions are emitted as well with the possibleexception of lubricant combustion We also have to be careful to say that hybrid engines never operateunder motoring conditions as the generator in a series APU can be used to rapidly decelerate the engine ifnecessary This could technically be considered motoring The issue at hand, PM emissions, are typicallyonly a result of positive changes in engine power due to the rapid addition of fuel to the engine and as aresult the effects of motoring are expected to have little if any effect on particulate emission from theseengines

- Off Highway Mobile Sources

- Constant Speed StationaryGensets

- On Highway Trucks

- On Highway Mobile Sources

Cycle

- Marine Sources

Table 3.1: Steady State Test Cycles