2003-01-3196 

Cold-Start and Warm-Up Driveability Performance of Hybrid

Electric Vehicles Using Oxygenated Fuels 

Matthew Thornton 

National Renewable Energy Laboratory 

Scott Jorgensen 

General Motors 

Beth Evans 

Evans Research Consultants 

Ken Wright 

ConocoPhillips 

Copyright © 2003 SAE International

ABSTRACT 

Hybrid vehicles may respond to fuel variables in unique 

ways; they could even require a unique driveability test. 

The Coordinating Research Council (CRC) conducted a 

program to determine the effect of ethanol content on 

driveability performance under cool ambient conditions. 

In addition to the 27 vehicles in the main fleet, four hybrid 

electric vehicles (HEVs) were tested using the same 

fuels and driveability procedure. These HEVs responded 

to fuel in a manner similar to conventional vehicles; 

however, the HEVs showed unique driving 

characteristics not well captured in the existing test. 

INTRODUCTION 

The Coordinating Research Council (CRC) Volatility 

Group conducted a program in January and February of 

2003 to determine the effect of ethanol content on coldstart and warm-up driveability performance under cool 

ambient conditions in a large group of late-model 

vehicles equipped with fuel-injection systems. The goal 

of the program was to develop concentration-dependent 

cold-start and warm-up driveability equations for the 

oxygenate offset of ethanol at cool ambient temperature. 

The Volatility Group tested 27 vehicles, which were 

selected from a total fleet of 80 vehicles, based on their 

response to driveability index (DI) using the highest DI 

fuel with the highest concentration of ethanol—10 

percent. 

In addition to these 27 vehicles, the CRC Advanced 

Vehicle Fuel and Lubricant (AVFL) Committee requested 

that the Volatility Group test a small number of hybrid 

electric vehicles (HEVs) using the same fuels and 

driveability procedure as the core program. The four 

hybrid vehicles tested included a Honda Civic, a Toyota 

Prius, and two Honda Insights. 

This paper details the analysis and results of the 

driveability performance testing from the four HEVs. The 

paper also includes a discussion of the four vehicles, the 

fuels used, the test location, procedures, and conditions. 

The results from the 27 conventional vehicles used in the 

core program will be published in a separate CRC report. 

The results of the test on the HEVs showed that, as with 

conventional vehicles, there is a statistically significant 

effect of fuel ethanol content on the driveability of HEVs. 

In addition, the three HEV models that were tested each 

acted differently and had individual idiosyncrasies that 

need to be taken into account. Whereas conventional 

vehicles can all be rated in the same manner, hybrid 

vehicles do not act similarly enough to be able to rate 

them using the conventional vehicle test method. This 

finding led to the conclusion that driveabilty test 

procedures unique to the evaluation of HEVs should be 

developed to better understand the performance of 

HEVs. The following will discuss these results and the 

recommendation for a specialized driveability test for 

HEVs. 

HYBRID ELECTRIC VEHICLES TESTED 

For this piggyback project four HEVs were used. These 

vehicles included one Honda Civic, two Honda Insights, 

and one Toyota Prius. The 2003 Civic rented for use in 

the project provided the newest production hybrid electric 

technology of the four vehicles. The mileage on the Civic 

at the end of the testing was 13,000. One 2000 Insight 

was provided by ConocoPhillips and had the highest 

mileage accumulation of all of the HEVs tested (16,600 

NREL/CP-540-41290. Posted with permission.

Presented at the 2003 SAE Powertrain & Fluid Systems Conference & 

Exhibition, October 2003, Pittsburgh, Pennsylvania 

1
mi). The National Renewable Energy Laboratory (NREL) 

loaned an additional 2000 Insight and a 2001 Prius to the 

project. These two vehicles had the lowest mileage 

levels of all four of the HEVs, 3200 and 6600 miles 

respectively. 

The Honda Insight and Toyota Prius were the first two 

HEVs commercially available in the United States. These 

two vehicles have some very basic similarities – both 

combine power from a gasoline engine with an electric 

motor and a nickel-metal hydride (NiMH) battery pack to 

provide motive force. The Honda Insight has a smaller 

pack that consists of 20 modules, each having six Dsized spiral-wound cells (see Figure 1). The total pack 

nominal voltage is 144 volts (V). The total energy 

capacity of the Insight pack is 936 Wh. The ends of the 

20 D-sized modules can be seen in Figure 1. Also shown 

are the fan and the outside of the ducting that directs 

cabin air across the modules for cooling. The larger 

Prius battery pack is a later generation NiMH design that 

consists of 38 prismatic modules, each having six, 1.2 V 

cells. The total pack nominal voltage is 273.6 V. The total 

energy capacity is 1778.4 watt hours (Wh). Figure 2 

shows the Prius pack with the 38 prismatic modules as 

they are arranged in the pack (3). 

The Honda Insight is a light-weight (856 kilogram (kg) 

curb weight), two-passenger hatchback powered by a 50 

kilowatt (kW) gasoline engine with additional assist 

power provided by a 10 kW electric motor. The Insight 

has a parallel HEV configuration and has manual 

transmission. The electric motor is coupled directly to the 

drive shaft of the engine and provides additional power 

for relatively hard accelerations. It also operates as a 

generator to recapture kinetic energy during deceleration 

and helps balance vibrations of the in-line three-cylinder, 

1.0-liter engine (4,5). 

The Toyota Prius is a five-passenger compact sedan 

powered by a 52 kW gasoline engine and a 33 kW 

electric motor. It has a curb weight of 1254 kg. The Prius 

has a more complex dual-mode hybrid configuration 

where energy to and from the vehicle wheels can travel 

along several different pathways. Mechanical energy to 

the wheels passes through a planetary gear set that 

couples the engine, electric motor, and generator to the 

final drive. Power to the wheels can be provided solely by 

the battery pack through the electric motor, directly from 

the gasoline engine to the wheels, or from a combination 

of both the motor and the engine. The battery pack can 

be recharged directly by energy taken from the wheels 

through the generator (regenerative braking) or from 

excess energy from the gasoline engine (also turning the 

generator) (3). The Prius utilizes an electronically 

controlled continuously variable transmission (ECVT). 

The Honda Civic is the most recent HEV to be released 

for public sales. The Civic is powered by a gasoline 

engine with an electric motor and a NiMH battery pack, 

similar to the Insight, although the four-cylinder, 1.5-liter 

engine is 50 percent larger. The Civic is a five-passenger 

compact sedan powered by a 63 kW gasoline engine 

and a 10 kW electric motor. The Civic is also configured 

with the continuously variable transmission (CVT). It has 

a curb weight of 1239 kg. The Civic has a battery pack 

that consists of 120 cells at 1.2 V each. The total pack 

nominal voltage is 144 V (6). 

Previous testing on the Insight and Prius at NREL 

provided some information related to the unique 

performance of these vehicles and their battery packs. 

NREL’s testing of the Honda Insight and Toyota Prius 

has revealed or quantified the results of a number of 

design differences that affect battery usage. These 

differences are due in part to the geometry and design of 

the packs, but also in large part to the design of the 

vehicle and control systems. Both vehicles have 6.5 

ampere hours (Ah) NiMH battery packs, but the Prius 

pack is a later-generation prismatic design that is also 

significantly larger, corresponding to the more intensive 

use of the car’s electric motor. The Prius’ 33 kW electric 

motor is used in a wider range of applications including 

all-electric propulsion under low-load, low-speed 

conditions. 

Testing showed that the Insight limited pack usage to 

approximately 60% of the rated 6.5 Ah capacity, while 

the Prius was limited to 40%. The Prius control strategy 

features a target indicated battery pack state of charge 

(SOC) of approximately 56%. Use of the battery and 

electric motor are strongly influenced by this target. The 

Insight apparently has a much broader range in which 

the SOC is controlled and no single target SOC. The 

Prius uses substantially more battery energy over a given 

driving cycle. For the Prius, the amount of propulsion 

energy supplied by the battery was nearly 10% of the 

gasoline fuel energy used by the engine on the Federal 

Test Procedure (FTP) driving cycle. The highest level of 

pack energy used by the Insight was 3% of the fuel 

energy for the SC03 cycle with air conditioning (3). The 

implications of these differences on the results of this 

program and impacts on future programs will be 

discussed in detail in a later section. 

Figure 1, Honda Insight Battery Pack 

2
Figure 2, Toyota Prius Battery Pack 

TEST FUELS 

The fuel matrix used for this program consisted of ten 

fuels; a high driveability index (DI) (1300) hydrocarbon 

base fuel with a nominal 7-psi vapor pressure and nine 

different blended test fuels. Three test fuels were 

prepared by splash blending 3, 6, and 10 volume percent 

ethanol into the base fuel (E1, E2, and E3). Three 

hydrocarbon-only test fuels were prepared by adding a 

light hydrocarbon mixture to the base fuel to roughly 

match the DIs (10%, 50%, and 90% evaporated points) 

of the three splash ethanol blends (H1, H2, and H3). The 

final three fuels were prepared by mixing 3, 6, and 10 

volume percent ethanol with hydrocarbon gasoline 

components to meet a constant 1300 maximum DI limit 

for all three fuels (E4, E5, and E6). Samples were 

obtained on-site and shipped to a volunteer’s laboratory 

facility for inspection. These specifications are shown 

below in Table 1. Indeed, all of the fuel used in this study 

exhibited a very high DI, all exceeding the maximum 

ASTM DI specification of 1250. The occurrence of fuels 

of this nature in the field, are currently rare, but they are 

occasionally experienced. 

Table 1. Test Fuel Specifications 

Inspection Units Base E1 E2 E3 H1 H2 H3 E4 E5 E6 

API Gravity °API 53.8 53.7 53.7 53.4 55.2 55.3 55.8 51.8 51.6 50.7 

Relative Density 60/60°F 0.7638 0.7638 0.7642 0.7654 0.7578 0.7577 0.7555 0.7721 0.7729 0.7766 

DVPE psi 7.81 8.91 9.02 8.90 8.77 8.81 8.90 7.91 8.00 8.00 

Oxygenates--D 4815 

MTBE vol% 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

TAME vol% 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

EtOH vol% 0.0 3.2 6.1 10.6 0.0 0.0 0.0 3.3 6.0 10.2 

O2 wt% 0.0 1.15 2.19 3.83 0.0 0.0 0.0 1.19 2.13 3.64 

D 86 Distillation 

 IBP °F 90.6 94.4 94.1 96.4 87.2 89.0 87.6 94.2 99.4 102.0 

 5% Evaporated °F 121.0 116.8 118.0 120.5 114.0 115.5 114.8 122.8 124.5 127.7 

 10% Evaporated °F 139.1 126.0 128.3 130.1 128.5 131.4 130.1 132.1 134.1 137.8 

 20% Evaporated °F 171.9 147.1 143.0 144.9 157.3 160.6 159.2 155.6 146.9 151.4 

 30% Evaporated °F 206.3 192.4 161.3 155.7 192.3 193.0 189.6 202.9 176.3 159.7 

 40% Evaporated °F 231.7 226.8 219.8 171.7 224.5 223.4 216.6 232.6 226.1 212.1 

 50% Evaporated °F 248.0 244.8 242.8 236.6 244.4 244.5 238.0 250.3 246.3 249.4 

 60% Evaporated °F 265.6 262.5 260.3 256.0 264.1 265.7 261.2 271.5 269.9 268.5 

 70% Evaporated °F 297.2 292.3 288.8 283.1 296.1 297.3 297.1 280.3 304.4 303.8 

 80% Evaporated °F 327.2 325.4 324.5 322.1 325.7 326.1 325.0 332.0 331.4 331.8 

 90% Evaporated °F 343.4 342.9 342.3 341.6 341.0 340.3 337.9 346.4 347.2 346.6 

 95% Evaporated °F 357.2 356.4 356.2 355.5 353.9 351.9 348.6 361.0 361.5 360.4 

 EP °F 386.3 380.7 384.9 382.4 383.0 379.9 376.6 390.8 390.9 386.2 

Recovery vol% 97.9 97.7 97.5 97.8 98.0 97.5 97.6 98.1 98.0 97.9 

Residue vol% 0.9 1.0 1.1 1.0 0.9 1.1 0.9 0.9 0.8 1.0 

Loss vol% 1.2 1.3 1.4 1.2 1.1 1.4 1.5 1.0 1.2 1.0 

Percent Evaporated 

at 158°F 

vol% 15.9 22.7 29.2 32.2 20.0 19.2 19.8 20.7 24.6 29.4 

Percent Evaporated 

at 200°F 

vol% 28.0 32.1 36.6 44.4 32.3 32.1 33.8 29.4 34.7 37.7 

Percent Evaporated 

at 250°F 

vol% 51.3 53.4 54.6 56.4 53.5 53.0 55.5 50.0 52.0 50.2 

Percent Evaporated 

at 300°F 

vol% 71.1 72.2 73.3 74.3 71.6 71.0 71.0 74.1 68.7 69.1 

Driveability Index 1295.9 1266.4 1263.3 1246.6 1267.1 1270.9 1247.0 1295.4 1287.2 1301.4 

3
TEST LOCATION 

The test program was conducted at the Renegade 

Raceways near Yakima, Washington, in the valley of the 

Yakima River. The raceways are at an altitude of 990 

feet. The test site was a 0.7-mile long, 60-foot wide, flat, 

paved, two-lane drag strip, along with several adjacent 

single-lane, paved, auxiliary roads normally used for 

racecar preparation. A large, rectangular, paved area 

suitable for defueling/refueling and vehicle storage also 

was utilized. The race staging area at the base of the 

track was used for soaking the vehicles overnight. 

TEST PROCEDURE 

The test fuels were evaluated as prescribed in the CRC 

Cold-Start and Warm-up Driveability Procedure (E-28-

94) (2). Duplicate tests were performed on every vehicle 

and fuel combination. 

The CRC Cold-Start and Warm-up Driveability 

Procedure consists of a series of light, moderate, and 

wide-open-throttle maneuvers mixed in with idles to 

obtain as many evaluations of driveability in a cold 

engine as possible (2). Figure 3 shows one of the 

Insights during an acceleration maneuver at the 

Renegade Raceway. Malfunctions are evaluated and 

recorded as being trace, moderate, heavy, or extreme. 

The absence of malfunctions was recorded as clear or 

clean. During set-up week, the raters were provided with 

all the test vehicles to set individual vehicle vacuum 

targets and more importantly to allow them to agree on a 

similar definition of malfunction severity. 

Figure 3. Insight During Acceleration Maneuver 

All vehicles were tested each day using three raters and 

three data loggers, with a specific rater assigned to 

exclusively test the same vehicles for the entire program. 

Three raters were used throughout the program. Each 

vehicle was assigned its own fuel each day. 

The three rating teams tested the fleet of 31 vehicles in 

three hours. Generally, three vehicles were on the track 

simultaneously, separated by approximately 0.3 miles. 

Overtaking a severely malfunctioning or stalled vehicle 

was accomplished in a safe predetermined manner. No 

problems with vehicles impeding one another were 

encountered using this schedule, even though stalls and 

severe malfunctions did occur. 

TEST CONDITIONS 

Temperatures at this location were stable for around 

three to four hours bracketing dawn. The overnight soak 

temperatures ranged from 22° F to 37° F (with the 

exception of one night at 15°F). The mean soak 

temperature was 31.9° F. All tests were carried out in the 

test-temperature range of 30° F to 42° F and 97.3 

percent of the tests for all the 31 vehicles fell inside the 

planned temperature window of 30° F to 40° F. The 

mean test-temperature was 37.0° F. 

RESULTS 

The results presented in this paper are divided into two 

sections: One section focuses on the analytical results 

while the second section discusses the subjective 

information gained from the program. Since all of the 

information reported in this section is limited to a small 

amount of data collected from only four HEVs, these 

results should not necessarily be applied to all HEVs. 

ANALYTICAL ANALYSIS 

Two data points were obtained for all four HEVs on each 

of the 10 fuels for a total of 80 tests. The diligent efforts 

of the field team produced data in a well controlled 

temperature range, despite the fact the hybrids were the 

last vehicles tested each day. If there was any danger of 

exceeding the specified temperature range for the 

primary test fleet the tests were postponed to the 

following day. All tests were conducted in a runtemperature window of 30°F to 42°F inclusive. 

Rater and vehicle are confounded in this analysis 

because each vehicle was assigned to a rater. Thus, any 

statements about rater or vehicle alone are unsupported; 

the variable car will present the combined effect. Car 

was treated as a class variable in all the analyses, while 

all the other variables were centered and treated 

numerically in the analysis. The SAS system for windows 

release 8.02 was used for the analysis (7). 

First the normality of the data was appraised using the 

SAS procedure proc Univariate. The data were 

reasonably normal (minimum 8, mean 60, maximum 

164, and standard deviation 36.8) but skewed 

(skewness=0.84), and the variance increased with 

magnitude. In order to more closely approximate the 

assumptions of normal statistics the transform 

Y=Ln(Total Weighted Demerits (TWD) +1) was used. 

This improved the normality of the dependent variable. 

The mean of the transform was 3.91 relative to a 

minimum and maximum of 2.2 and 5.1, with a standard 

deviation of 0.68, and a skewness of -0.44 (see 

Appendix A). 

4
Having established a normal dataset, the analysis was 

conducted on centered variables using proc GLM. All 

nonsignificant variables were dropped. The effects that 

remained were car, soak, ethanol, and DI, plus an 

intercept. Car, DI and the intercept were significant at 

alpha=0.0001 (99.99% confidence), while ethanol and 

soak temperature were significant at alpha =0.014 and 

0.044 respectively. The coefficients are provided in Table 

2, below. 

Table 2. Regression Statistics 

Standard 

Parameter Estimate Error t Value Pr > |t| 

intercept -0.857108113 B 0.08646489 -9.91 <.0001 

Car 84 1.150603940 B 0.12228066 9.41 <.0001 

Car 85 1.116298275 B 0.12227970 9.13 <.0001 

Car 86 1.161530238 B 0.12227970 9.50 <.0001 

Car 87 0.000000000 B 

DI 0.010832567 0.00229222 4.73 <.0001 

ethanol 0.028083738 0.01110476 2.53 0.0136 

soak -0.019839109 0.00968464 -2.05 0.0441 

Car is a class variable that represents the contribution of 

the car/driver combination, DI is a continuous variable 

representing the driveability index in degrees F, ethanol 

is a continuous variable representing the percent 

ethanol, and soak is a continuous variable representing 

the overnight minimum temperature in degrees F. The 

“B” following some of the estimates indicates that the 

result is referenced to a specific class level being set 

arbitrarily to zero. In this case all the other car/rater 

combinations are referenced to car/rater 87. The 

intercept is also referenced to this value. This process is 

common when class variables are used. It cannot be 

over emphasized that the results and significance levels 

apply to this fleet in this test, not to all HEVs. 

The overall regression has an F value of 28.05 and a 

probability of higher F of <0.0001. Car rater combinations 

84, 85, and 86 were all significantly different from 

car/rater combination 87 (see Table 2), but were not 

significantly different from each other (90% confidence 

level). 

Least squares (LS) means (a best estimate of the mean 

taking all other factors into account) were calculated for 

each vehicle and in a separate regression with fuel as a 

class variable for each fuel. The results are presented 

graphically below in Figures 4 and 5. The six splash 

blended fuels were not significant from each other (90% 

confidence level) overall regression F=15.3, Pr>F 

<.0001. The lower match blends were not different from 

the base fuel, but the highest blend (fuel E6 in Figure 4) 

was different (90% confidence level) overall regression 

F=15.3, Pr>F <.0001. The two higher ethanol content 

match blends were significantly different from all splash 

blends (98 to 99.99% confidence level) but the lowest 

match blend was generally not different from the spalsh 

blends (90% confidence level overall regression F=15.3, 

Pr>F <.0001). The two Insights and Prius were not 

significantly different (90% confidence level), but were 

different from the Civic (99.99 confidence level overall 

regression F=28.05, Pr>F <.0001) see Figure 5. 

LS mean TWDs

0

10

20

30

40

50

60

70

80

90

E1 E2 E3 H1 H2 H3 E4 E5 E6 

fuel

TWD

PRNT

Match blends

Hydrocarbon splash blends

Base

Ethanol splash blends

Figure 4. HEV Driveability Fuel Dependent Results 

LS mean TWDs

0

10

20

30

40

50

60

70

Insight 1 Insight 2 Prius Civic

LS Mean TWD

Figure 5. HEV Driveability Test Demerit Results 

SUBJECTIVE ANALYSIS

The three hybrid models each act differently and have 

individual idiosyncrasies, which must be taken into 

account. Whereas conventional vehicles can all be rated 

in the same manner, hybrid vehicles do not act similarly 

enough to be able to rate them all in the same manner 

with the current test. 

The first obvious challenge is that the CRC Driveability 

Procedure was developed for automatic transmissions; 

however, the two Insights were equipped with manual 

transmissions. One rater was assigned both Insights in 

this program in an attempt to omit the shifting variability 

inherent among drivers. The rater determined the shift 

points for each maneuver before the test program 

began. The rater determining the shift points attempted 

to simulate the shift points of an automatic transmission 

so that the transition between gears was as natural as 

possible. Different shift points may be necessary for 

different models. Also, there is only one idle rating 

applicable during the starting procedure; there is no 

“Drive” idle rating. The detent maneuver is not applicable 

5
for manual transmissions either; detent was performed at 

wide-open-throttle in second gear. 

The Insights also have an idiosyncrasy in their start 

times. Several times, they would quit cranking before the 

normal five seconds allowed. The rater would still have 

the key in the crank position, but they would stop 

cranking on their own. The rater would then release the 

key, turn the key off and on again to re-pressurize the 

fuel rail, and begin cranking again, and the same thing 

might or might not happen. These were recorded in the 

database as no-starts, although a conventional no-start 

situation occurs when the vehicle continues cranking for 

five seconds and does not start. 

All four of the HEVs tested in this program used the 

electric motor to start the engine rather than conventional 

starters. It was observed that while on tank fuel, the 

Prius would start so imperceptibly that it was impossible 

to tell when it actually started. The rater was concerned 

how to record start times during testing. When the same 

vehicle was started on test fuel, the cranking time 

became obvious and the rater could tell exactly when the 

vehicle started. This could be an issue if testing a fuel 

that gives good starting performance. 

One of the idiosyncrasies of the Prius is that it would 

completely stall and then re-start the engine on its own, 

with no action on the rater’s part. This occurred several 

times with the Prius and once with one of the Insights. 

This behavior is not well captured with the current test. 

Hybrids can be designed to operate differently, such as 

the Honda and Toyota vehicles tested. The Honda HEVs 

provide electric motor assist to a small gasoline engine 

during take-off and acceleration. When slowing down or 

braking, energy is recaptured by the same motor serving 

as a generator. Like the Prius, the Honda system 

incorporates an idle-stop feature that shuts off the engine 

at traffic lights. The Toyota Prius operation is based on 

the driving mode the vehicle is under. The Prius 

operation can be by the gasoline engine, the electric 

motor, or a combination of both. 

Conventional ratings do not always apply to the hybrids. 

One example is with the Prius. The rater testing the Prius 

had to develop a unique rating scheme for hesitation with 

that car. The car would move forward when the 

accelerator was depressed, but fuel quality had a definite 

impact on the car’s movement. The car might move 

forward with the vacuum staying at the idle vacuum 

(nominally 15 inches). Sometimes the car might move 

forward with a delay in the vacuum dropping to the three 

inches of light-throttle vacuum. Other times the car might 

move forward with an immediate vacuum response. 

Sometimes, the rater could feel the engine engage or 

“kick in” and sometimes the rater could tell the engine 

had not “kicked in” during the maneuver. 

The preconditioning cycle is another area in which the 

hybrids are very individualistic. Each model required a 

different preconditioning cycle to adequately recharge 

the assist battery. Depending upon the way the Insights 

were driven, they could use the same preconditioning 

cycle the conventional vehicles used; however, if they 

were not driven optimally, this cycle could deplete the 

assist battery to less than a quarter charge. The Civic 

required excessively mild accelerations or the battery 

would be completely depleted, and it could not use the 

conventional preconditioning cycle. The Prius could be 

preconditioned using the conventional cycle, but it 

required moderately mild accelerations. It quickly 

became obvious that the preconditioning drivers needed 

to be “trained” how to drive the vehicles to successfully 

charge them. 

The battery charge seems to affect when the battery 

assist engages. The battery-assist appears to affect 

engine vacuum. There is some question whether the 

battery-assist on the hybrids can either simulate or 

cover-up malfunctions when it engages. The raters made 

every effort to rate fuel-related malfunctions rather than 

battery-oriented behavior. Increasing familiarity with the 

operation of the various hybrids made it easier to 

distinguish between fuel-related malfunctions and 

battery-oriented behavior. The raters agreed that 

becoming familiar with the vehicles is a necessity; in fact, 

in most cases, it took about a week of testing before the 

raters began to feel comfortable with the hybrid assigned 

to them. 

All the hybrid vehicles were de-fueled, flushed, and 

refueled using a modified version of the standard CRC 

fueling procedure. The standard fueling procedure had 

been developed by the CRC Volatility Group from a study 

to reduce fuel carryover from one test to the next when 

flushing vehicle fuel tanks (2, 8, 9). Figure 6 below 

shows the two Insights during de-fueled, flushed, and 

refueled. 

Figure 6. Two Honda Insights Being De-fueled, Flushed, 

and Refueled 

Changes to the refueling procedure were to address 

concerns on battery state of charge and time to refuel. In 

order to maintain constant battery charge levels, the 

6
engines were operated during de-fueling. To reduce 

overall refueling time, the amount of gasoline used to 

flush and refuel was changed from four gallons to two 

gallons. Since these hybrid vehicles had smaller fuel 

tanks than conventional vehicles, smaller fill size is 

allowed in the CRC fueling procedure. But even at a 50% 

reduction in fuel to be drained, the Civic and Prius took 

longer to de-fuel than most other test vehicles. The drain 

valve on the Insights needed to be adjusted every five 

minutes or so, or else surging from the fuel pump would 

stall the engine. With close attention, the Insights could 

be drained in an acceptable 20 to 30 minutes. While the 

program was able to accommodate the varying defueling rates, this should be taken into account when 

planning future hybrid performance testing. If equipment 

were available to maintain the battery level to fully 

charged while running the fuel pump, it would simplify the 

de-fueling by not having to run the engine. 

DISCUSSION 

The results of these tests must be taken as qualitative, 

not quantitative, for three reasons. The “fleet” consists of 

only four vehicles and two are of the same make and 

model. This sample size is certainly insufficient to draw 

conclusions about HEVs as a class. Secondly, the 

vehicles tested best represent the initial sales in the US, 

as such they are indicative but not definitive of the 

response to fuel for the complete family of HEVs that will 

soon be available. Finally, as the subjective results 

indicate, there is significant reason to believe a more 

complete cold start and driveaway test could be devised 

to better evaluate hybrid response to fuel. It is possible 

that these results do not fully capture the fuel response 

for even this fleet of vehicles. For these reasons, the LS 

means have been left graphical, and this discussion will 

speak primarily in terms of significant or non significant 

response rather than in numerical terms. The primary 

observations supported by the analytical analysis are: 

hybrid vehicle/rater combinations can be discriminated 

with the current test, HEVs do show a response to fuel 

variables, and the response is trend-wise similar to that 

of a fleet of current conventional vehicles. 

The vehicle LS means analysis and the GLM analysis 

both show a significant difference between the Civic and 

the other three vehicles. While the Civic technology is 

mildly different from that of the other vehicles, it must be 

remembered that the rater is totally confounded with the 

vehicle in these analyses, so no meaningful statements 

can be made about the vehicle alone. Still, it is clear that 

at least differences in rater-vehicle combinations can be 

discriminated by the existing cold start test process. 

The fuel response across the four vehicles is significant 

in the GLM and the LS means analysis, indicating that 

fuels can be discriminated. As might be expected, based 

on the literature treating fuel interactions with 

conventional vehicles, the higher DI fuels have higher 

TWD (99.99% confidence level) and ethanol degrades 

performance. In addition, GLM results indicate that the 

effect of 1% ethanol relative to one point of DI (°F scale) 

is similar to that observed when the main fleet is 

analyzed in the same fashion (2). While this similarity 

could not be predicted with certainty a-priori, the fact that 

HEVs still use a standard internal combustion engine 

(ICE) makes this result quite reasonable. 

The qualitative fuel results are also in accord with past 

work (10). While the fleet size cannot justify numerical 

comparison of means and model effects, it is reassuring 

that the response observed is in general accord with 

extensive past experience. However, there is significant 

reason to believe a better cold-start and warm-up 

driveability test could be created for use specifically with 

HEVs. 

Based on this conclusion the authors and the CRC AVFL 

committee intend that this piggyback project be followed 

by a workshop that will focus on the development of a 

more complete and appropriate HEV cold start 

driveability test. 

The unique operation and performance of HEVs, as 

discussed above, support the need of such a workshop. 

There are several HEV issues that should be evaluated 

during the workshop. They include, but are not limited to, 

an appraisal of those parts in the existing CRC E-21-94 

cycle and warm-up schedule that are inappropriate for 

HEVs, an appraisal of new or unique aspects of HEV 

function that interact with fuel, and could require new 

maneuvers to address, a de-fueling and fueling process 

for HEVs, a warm-up procedure for HEVs including a 

standard initial SOC that will contribute to assessment of 

fuel interactions in HEVs, and a way to obtain that SOC 

with acceptable reproducibility, a cold-start and 

driveaway test based on the CRC E-21-94 procedures 

specifically tailored to effectively determine the cold-start 

and driveaway driveability of HEVs, and possibly a 

demerit calculation system modification to calculate 

TWDs over the HEV cycle. 

CONCLUSION 

The findings here, although limited, are important to the 

future testing and evaluation of HEVs. HEVs showed 

significant variation among vehicle/rater combinations 

and among fuels using the existing CRC cold-start and 

warm-up driveability test, indicating that there is a 

purpose in testing the driveability of this class of vehicles. 

Using the existing test, hybrids responded to fuel in a 

manner similar to the conventional vehicles that were 

tested. In addition, the HEVs tested had unique driving 

characteristics that made implementation of the existing 

CRC cold-start and warm-up driveability test problematic. 

Therefore, a driveability test specifically tailored to HEV 

characteristics is recommended in order to properly 

evaluate this class of vehicles. To accomplish this a new 

warm-up and refueling process will also be required. 

7
ACKNOWLEDGMENTS 

The authors and the AVFL Committee wish to 

acknowledge the dedicated and professional work of the 

Volatility group of the CRC who conducted the testing 

and collected the data presented in this report. The 

authors would also like to thank Harold “Archie” 

Archibald, Phil Van Acker, Jeff Jetter, and Marie 

Valentine for their contributions and assitance in 

developing this report. The AVFL Committee also wishes 

to thank the Yakama Nation and the owners of the 

Renegade Raceway for use of the facility. 

REFERENCES 

1. SAE 2003-01-0083: “Development of a Power Train 

for the Hybrid Automobile – The Civic Hybrid” 

2. Coordinating Research Council, Inc., 2003 CRC 

Intermediate-Temperature Volatility Program, CRC 

Report No. 638, to be published by CRC in late 

2003. 

3. Kelly, Mihalic, and Zolot, Battery Usage and Thermal 

Performance of the Toyota Prius and Honda Insight 

during Chassis Dynamometer Testing, The Seventh 

Annual Battery Conference on Applications and 

Advances. 

4. Toyota Prius: Best Engineered Car of 2001, 

Automotive Engineering International, Society of 

Automotive Engineers, Warrendale, PA. 

5. Honda Sales Insight – Insight Facts Book, Honda 

Motor Company. 

6. Honda website; 

http://www.hondacars.com/models/model_overview.

asp

7. SAS windows release 8.02, Users Guide Version 6, 

4th edition, Cary NC, 1989. 

8. Coordinating Research Council, Inc., CRC Report 

No. 629, 2001 CRC Hot-Fuel-Handling Program, 

Appendix C, June 2002. 

9. A Report on a Vehicle Fuel Tank Flush Effectiveness 

Evaluation Program, SwRI Project 08-31088, August 

20, 2001, Prepared for CRC in response to CRC 

Project No. CM-138-01/1. 

10. 1995-1997 CRC Study of Fuel Volatility Effects on 

Cold-Start and Warm-up Driveability with 

Hydrocarbon, MTBE, and Ethanol Gasoline: 

Summary Report for Phases 1, 2, and 3, CRC-613, 

December 1998. 

DEFINITIONS, ACRONYMS, ABBREVIATIONS 

AVFL: advanced vehicle fuel and lubricant

Ah: ampere hours 

CVT: continuously variable transmission 

CRC: Coordinating Research Council

DI: driveability index 

ECVT: Electronically controlled continuously variable 

transmission 

F: Fahrenheit

FTP: Federal Test Procedure 

HEV: hybrid electric vehicle 

ICE: internal combustion engine 

kg: kilogram 

kW: kilowatt 

LS: least squares 

NREL: National Renewable Energy Laboratory

NiMH: nickel-metal hydride 

SOC: state of charge 

TWD: total weighted demerits

V: volts

Wh: watt hours 

APPENDIX A 

Discussion of the Merits of Log Transformation: 

The log transform used is not uncommon in improving 

the treatment of datasets where the dependent variable 

spans two orders of magnitude; it has been used 

extensively and effectively in past CRC programs. The 

transform is taken for TWD+1 to avoid an infinite result in 

cases where there are no demerits observed. A 

significant byproduct of the transform is that the effects 

of the variables in a linear analysis (such as GLM) 

become multiplicative and the coefficients determined 

become exponents when the reverse transform is taken. 

That is to say, the resulting model will be of the form 

Ln(TWD+1)=Av1+Bv2+Cv3+... TWD=v1A*v2B*v3C...-1 

where the A, B, and C are the coefficients determined in 

the regression, and the vi are the variable values while 

the Vi are the exponential of the variables, e.g. 

V1=exp(v1)=exp(DI) where DI is the centered value of 

driveability index. 

8