~ Pergamon Energy Com,ers. Mgrnt Vol. 38, Suppl., pp. $455-$460, 1997 © 1997 Elsevier Science Ltd. All rights reserved

Printed in Great Britain PI I : S0196-8904(96)00310-X 0196-8904/97 $17.00 + 0.00

Technology Assessment of Alternative Fuels by CO2 Fixation Use in Passenger Cars

Seiji Matsumoto, Atsushi Inaba National Institute for Resources and Environment(NIRE),

16-3, Onogawa, Tsukuba, Ibaraki, 305, Japan

Yukio Yanagisawa Research Institute of Innovative Technology for the Earth(RITE),

Kizu, Kyoto 619-02 Japan, / Harvard School of Public Health

ABSTRACT

Alternative fuel vehicles were investigated as a possible mitigation measure to reduce CO2 emissions. Fuel economies of several alternative cars were compared, and integrated CO2 emissions from fuel mining to consumption in Japan were calculated. The alternative fuel vehicles we investigated were methanol, compressed natural gas, electric, hydrogen, hybrid (internal combustion engine and motor), and fuel cell vehicles. Our calculations showed that a combined approach discharged the least amount of CO2 when compared to individual alternative fuel vehicles studied in this paper. The combined approach was to use methanol and electricity coming from a coal fired power plant. Methanol was produced from CO2 collected from the flue gas of the coal fired power plant and hydrogen originated from a non-carbon natural energy source. The MeOH-powered vehicle emitted 28.5 kg- CO2 per 100 km driven. Electricity generated at the coal fired power station could be supplied to the electric vehicles. The CO2 emission per 100 km driven was reduced to 16.7 kg by the combination of the methanol and electric vehicles. CO2 recycling for methanol production will be one of the CO2 mitigation strategies in the transportation sector, if hydrogen can be produced plentifully from renewable energy sources. The methanol vehicle is also advantageous when considering available infrastructures. © 1997 Elsevier Science Ltd

KEYWORDS

CO2, Alternative fuel, vehicle, Methanol, CO2 recycling

INTRODUCTION

Carbon dioxide (CO2) emission from the transportation sector accounts for approximately 20% of the Japanese total CO2 emissions, and its growth rate is faster than other sectors. More than 90% of CO2 emission in the transportation sector comes from vehicles mostly using petroleum as an energy source. There are several mitigation measures to reduce CO2 emissions from the transportation sector, such as improving fuel efficiency and systematic control of traffic flows. In this paper, we focused on the use of alternative fuel vehicles as a mitigation measure to reduce the CO2 emission. Methanol, compressed natural gas, electricity, and hydrogen were selected as alternative energy sources for driving vehicles. We carried out technological assessments on these vehicles from viewpoints of energy efficiency and CO2 emission potential.

METHODS

A vehicle needs specific forms of energy converted from primary sources such as oil, natural gas, coal and renewable energy sources including solar, wind and hydraulic power. Since CO2 is discharged from

$455

$456 MATSUMOTO e/al.: ALTERNATIVE FUEL VEHICLES

each step of the energy conversion, a full fuel cycle analysis, covering the mining of the primary energy source, transportation, conversion and consumption by the vehicle, was carried out to assess an integrated CO2 emission for each alternative fuel. We included CO2 emissions not only from mining and conversion, but also transportation processes from producing countries to Japan, because Japan imports almost all primary energy sources. Standardizing driving modes is important for comparing fuel economy, because mileage or fuel economy depends on the driving modes of the vehicle. In Japan, the fuel economy is indicated by several ways such as 60 km/h constant driving mode, 10-mode representing driving conditions in an urban area, 11-mode simulating early morning driving situations beginning from cold engine start, and 10-15 mode including high speed drives on free ways. We selected 10-mode as the basis for the fuel economy comparison because it represents typical driving patterns in urban areas and because of the availability of the mileage data.

RESULTS

FUEL ECONOMY

Methanol Vehicles. Fuel economy data for the Corolla-FFV (TOYOTA) are available for the firing both gasoline and methanol. Fuel consumption using high-octane gasoline is 13,7 km/l(compression ratio, Rc=l 1), while the mixture of 85% methanol and 15% of gasoline is consumed at the levels of 7.88 km/l-M85. This value is equivalent to 13.8km/IGE (kin traveled per one liter gasoline equivalent). Fuel economy of the Corolla-1600, which is a base car of the FFV, is 13.2kin/1 using normal gasoline. This mileage is lower than that oftbe FFV because of the lower compression ratio. Since the octane value of methanol is higher than that of gasoline and methanol can be burned at leaner conditions than gasoline, we expected improvement of thermal efficiency of the methanol vehicle.

Comnressed Natural Gas (CNG) Vehicles. Fuel consumption of a CNG vehicle is reportedly 13.8 km/IGE (Wagon, Rc=9.2). The disadvantages of the CNG vehicle are the larger aerodynamic friction due to a larger fuel tank and energy loss due to gas compression. These reduce the fuel economy by 17%. The octane value of methane is 130, higher than those of methanol and gasoline. Improvement in thermal efficiency is expected by increasing the compression ratio. For example, when Rc is raised from 8.2 to 13.2, thermal efficiency is reported to be improved by 22.2%. Lean burning of CNG has a similar effect to that in the methanol engine, where a 5% improvement of fuel consumption was found.

Electric Vehicles {EV). The EV model used for comparison purposes was the Roadster (MAZDA), for which gasoline consumption is 11.2 km/1. Energy consumption of Roadster-EV is 43.3 km/IGE in 10- mode and 69.8km/1 at the 60km/h constant mode. The 10-mode efficiency is nearly 4 times greater than that of the gasoline vehicle. These results were then compared to those of the IMPACT ( GM ), an original EV car designed to reduce body weight and aerodynamic friction as much as possible. The fuel consumption of the IMPACT is approximately half of the Roadster EV. The technologies applied to the IMPACT to enhance energy efficiencies can be used in the other alternative fuel vehicles. In these calculations, we excluded energy loss due to electricity generation and battery charging.

Hydrogen Vehicles (HV). Since vehicles with an internal combustion hydrogen engine are still at an experimental stage, we could not get fuel consumption data of HV at standardized running modes such as 10-mode. Therefore, fuel consumption of HR-X2 (MAZDA) in 10-mode was estimated to be about 10km/l based on the data taken in constant speed running mode.

Hybrid Vehicles. Hybrid vehicles can be made by various combinations of power generation units such as an internal combustion engine and motor. DASH21 (Daihatsu) is a light duty ear equipped with a 660ml gasoline engine, electric generator and motor. Its fuel consumption rate at 10-mode is 29 km/IGE and 32 km/IGE at 10-15 mode. The advantage of the hybrid vehicle is its flexibility in engine use. For example, the main engine is not always required to meet full loads by expecting assistance from a sub- power unit.

Fuel Cell Vehicles (FCV~. A fuel cell (FC) is one of the direct power generation systems converting chemical energy to electric energy without significant heat generation. Higher thermal efficiency is

MATSUMOTO et al.: ALTERNATIVE FUEL VEHICLES $457

theoretically expected than internal combustion engines. Among several types of FC under development, we think that FC equipped with Proton Exchange Membranes (PEM) is the most promising for

passenger cars, since 0) the power per unit weight of FC is large, (~) response time is quick, and (~)

operation temperature is relative!y low. If we operate FC using carbon-based fuels such as alcohol and hydrocarbon, CO must be carefully removed to avoid catalyst poisoning in the PEM. A prototype FCV made by MAZDA showed the fuel consumption rate of 44 km/IGE. However, details of testing conditions were not known.

INTEGRATED CO2 EMISSIONS

For the full fuel cycle CO 2 emission analysis for alternative fuel vehicles, CO2 emissions per 100 km driven by 1500 cc or 1600 cc alternative fuel passenger cars were calculated for fuel consumption under the 10-mode driving condition. CO2 emissions for fuel production corresponding to 100 km driven were added. CO2 emissions due to mining and transportation from the mining country to Japan must also be added to CO2 emissions for driving and fuel production. Table B summarizes the results of our calculations.

Gasoline-Fueled Vehicles. CO2 emission of a gasoline-fueled Otto-cycle engine car was calculated as follows. Gasoline consumption is 7.3//100km under the 10-mode driving condition, shown in Table A. Since a calorific value of gasoline, carbon mass ratio and specific gravity are 43.5MJ/kg, 0.85 and 0.75, gasoline consumption and CO2 emission per 100 km driven became 5.47 kg and 17.1 kg- CO2

respectively {7.3 x 0.75 x 43.5 × (1/43.5) x 0.85 x (44/12)--17. l(kg- CO2/100km)}. The integrated CO2

emission, 20.8 kg- CO2, was obtained by adding 3.66 kg- CO2 emitted from the refinery assuming CO2 emissions of 0.67 kg/kg gasoline produced from crude oil.

Methanol Vehicles ( MV ). Fuel consumption of an M85 (85% methanol and 15% gasoline) fueled Otto-cycle engine car under the 10-mode driving condition is 7.25 IGE/100km, as shown in Table A. If the energy consumption of M100 (100% methanol) methanol fueled car was equal to the M85 engine, 11.83 kg of MeOH was required to drive for 100km, and CO2 emission was 16.3 kg using the calorific

value of methanol, 20MJ/kg {7.25 × 0.75 × 43.5 × (1/20) × (12/32) x (44/12)=16.3(kg- CO2/100km)}.

The integrated CO2 emission became 23.7 kg/100 km by adding CO2 emissions of 0.23 kg/kg MeOH produced from the conversion of LNG and 0.395 kg/kg MeOH produced corresponding to the mining of natural gas.

CNG Vehicles. Fuel consumption for a CNG car is 7.27 IGE/100km, as shown in Table A. As caloric value of natural gas is 45.1 MJ/kg, 5.25 kg of methane is consumed to drive 100 km, corresponding to

14.5 kg- CO2 emitted {7.27 x 0.75 x 43.5 x (1/45.1) x (12/16) x (44/12)--14.5(kg- CO2/100km)}.

If 0.608 kg- CO2 emission per kg methane is assumed for mining and transportation, 17.7 kg of the integrated CO2 would be emitted per 100km driven.

EV. Electricity consumption of Roadster (MAZDA) on the 10-mode driving condition was calculated to be 2.31 lGE/lOOkm, as shown in Table A. Assuming 30 MJ/kg as the calorific value for coal, 35% thermal efficiency for a coal fired power plant, and a carbon mass ratio for coal of 0.7, coal consumption at the power station and CO2 emissions per 100 km driven was calculated to be 7.18 kg and 18.4 kg-CO2,

respectively {2.31 × 0.75 × 43.5 × (1/30) x (1/0.35) x 0.7 × (44/12)=18.4(kg- CO2/100km)}.

If 30% energy loss for transmission and charging is assumed, CO2 emitted per 100 km driven is 23.6 kg

{ 18.4-0.7=26.3 (kg- CO2/100km)}. If 0.131 kg CO2 emitted per kg coal is assumed for mining and

transportation, 1.34 kg of CO2 is emitted from mining and transportation of 10.3 kg-coal, which was calculated by 7.18 kg-coal divided by 0.7. The integrated CO2 emission was 25.0 kg- CO2/100km.

HV~ Energy Consumption by HV is 6.21 l-GE/100km at constant speed running mode and the calorific value of hydrogen is 121 MJ/kg, leading to hydrogen consumption per 100km driven of 1.674 kg-H2. Although hydrogen vehicles do not emit CO2 in the exhaust, CO2 emissions for electricity generation

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from coal and for electrolysis must be counted. Here, 48.8kWh of energy consumption per kg hydrogen

produced by electrolysis was assumed {6.21 x 0.75 x 43.5 x (1/121) x 48.8 x (3600/1000) x (1/0.35) x

(1/30) x 0.7 x (44/12)=71.9(kg- CO2/100km)}. As 28.0 kg of coal is required in this system for 100 km

driven, CO2 emissions for mining and transportation are 3.65 kg, as shown in Table B. Assuming HV consumed hydrogen at a rate of 10 l-GE/100km under the 10-mode driving condition, CO2 emissions

were calculated to be 115.8 kg- CO2 {71.9 x (10/6.21)=115.8(kg-CO2/100km)}. When hydrogen is

produced from methane by shift reaction using water, 17.87kg- CO: is emitted to produce 1 kg of

hydrogen. CO2 emissions then become 29.8 kg- CO2 { 1.674 x 17.87=29.8(kg- CO:/100km)}.

MV and EV based on a CO, recycling system. Methanol vehicles need 11.83kg-MeOH to travel 100km, as was calculated in a previous section. When methanol is produced from the recycled CO: separated from flue gas of a coal-fired power station, energy for CO2 separation of 0.256 kWh/kg- CO2 was needed for a membrane technology of 60% separation efficiency. A 0.35 kWh/kg-MeOH is required to produce methanol under 95% of CO: conversion. The total energy to produce methanol from flue gas was determined to be 0.721 kWh/kg-MeOH. During these CO2 transformation steps, 43% of the separated CO2 from the flue gas was exhausted to the atmosphere and remaining 57% was converted to methanol. The amount of coal consumed by the power plant to produce 11.83 kg methanol for 100 km driven is

11.12 kg {11.83 x (12/32) x (1/0.7) x (1/0.57)=11.12 (kg-coal/100km)}.

Although 32.4 kWh of electricity was generated by the plant {11.12 x 30 x 0.35 x

(1000/3600)=32.4(kWh)}, 8.53 kwh was consumed to produce 11.83 kg of methanol {0.721 x

11.83=8.53(kWh)}. CO2 was discharged from the power plant, CO: transformation steps and MeOH

vehicle operation at the rates of 28.5 {11.12 x 0.7 x (44/12)=28.5(kg-CO2)}, 12.3 {11.12 x 0.7 x

(44/12) x (0.43)= 12.3(kg- CO2)} and 16.2 { 11.12 x 0.7 x (44/12) x (0.57)=16.2(kg- CO2)} per 100km

driven.

EV can run 79.9 km {23.9 x (1-0.3) x {2.31 x 0.75 x 43.5 x (1000/3600) x 100=79.9km} using 23.9

kwh {32.4-8.53=23.9} under 30% electricity loss due to transmission and charging. This yields 179.9 km total driving distance by both the EV and methanol vehicle. As EV does not exhaust CO: during the

driving, only 15.8 kg of CO2 is emitted per 100 km driven { 28.5 - (179.9/100)= 15.8(kg- CO2/100km) }

if no CO2 emission for hydrogen production can be assumed. If hydrogen would be produced from methane using shift reaction, 2.7 kg of CO2 is emitted per 1 kg of methanol production. This process adds 3 ! .9 kg of CO2 to the 28.5kg- CO: emitted per 100 km driving of MeOH vehicle. CO: emissions per 100 km driven for MeOH vehicle and EV are then increased to 33.6

kg {6x ll.83--32=2.22(kg-H2), (31.9+28.5)--(179.9/100)=33.6(kg-CO:/100km)}. Hydrogen must

be supplied by a non-carbon renewable source.

CONCLUSIONS

We compared performances of alternative fuel vehicles and their resulting CO2 emissions from the full fuel cycle aspects. CO2 emissions for CNG vehicles were the lowest among the alternative fuel vehicles investigated, even if fuel treatment was taken into account. A vehicle using MeOH produced from natural gas emits 23.7 kg of CO2 per 100 km driven. If MeOH is produced from CO2 separated from flue gas of the coal-fired power plant and hydrogen is produced by non-carbon natural energy process, a MeOH vehicle emits 28.5kg- CO2 per 100 km driven. Since electricity generated at the coal-fired power plant can be used to power EV, CO2 emissions can be reduced to 16.7 kg per the 100 km driven for this case which powers both EV and MeOH vehicles. Although a non-carbon natural energy process must

MATSUMOTO et al.: ALTERNATIVE FUEL VEHICLES $459

be used to produce hydrogen for this system, the result of this calculation shows the possibility of CO2 reduction in the transportation sector by recycling CO2 from flue gas to methanol.

ACKNOWLEDGEMENT

This study was supported by NEDO Organization).

(New Energy and Industrial Technology Development

REFERENCES

Arakawa, M., et al., MAZDA Technical Paper No. 12, p.97,(1994) Araki,S., et al., Proc. of 1 lth Energy-System & Economics Conf. JAPAN, p.319,(1995) Ariyoshi,M.,'Hybrid Vehicle', Proc. of EV Forum '95 JAPAN, p.254,(1995) Dept. of Global Environ., EA. JAPAN ed., Global Warming Measure Technol. Handbook No.4, p. 130, (1992), Daiichi-Hoki Fujinaka,M., 'Electric Vehicles', Sangyo-Kogai, Vol.29, No.3, p.283(1993) Hasegawa,Y., et al., 'Fuel Cell Vehicle', MAZDA Technical Review No. 12, p. 103, (1994) IAE, IAE-C-8922(1990) MAZDA Co., Brochure of Hydrogen Vehicle, (1994) SAE of Japan ed., Index Tables of Japanese Automobiles 1994,(1994), SAE of Japan Tsukasaki, et al., 'Collora-FFV', TOYOTA Technical Review, Vol.42, No. I, p.93, (1992) Takahashi,T., "Vivio-EV', Proc. of 3rd Transport. & Disribut. Div. JSME, p.83, (1994) Watanabe, T., 'Natural Gas Vehicles' Sangyo-Kogai, Vol.29, No.3, p.283, (1993) Yoshino, M., Proc. of EV Forum'95 JAPAN, p.246, (1995)

Fossil Fuel (Petro, NG, Coal, etc)

I Renewable Energy (soler, hydro, wind, eto)

C02

IFue I =J Gaso I i ne V ~lProcess in¢ Diesel V

Generation CO 2 ~ = " l " I gethanol ~ geOHV

,, _ = = = = = ~ Power

Generation

Fig. 1 Energy Flow of Vehicles

$460 MATSUMOTO et al.: ALTERNATIVE FUEL VEHICLES

Table A Comparison of Vehicles

Toyota

Dri~ng mode

10-mode

energy consump.

13.7kngl

Mileage of gasoline eq. 0an/IGE)

13.7

Energy Consump. per 100kin drive

0GWlOOm) 7.3

Driving Range per 1MJ

0.42 Corolla- 1600 Toyota ibid. 7.88km/1 13.8 7.25 0.424 Corolla-FFV WAGON-type ibid. 180km/ 13.8 7.27 0.422 1500¢c(CNG ) 11.2Nm^3 GM-IMPACT 50km/h 200km/i3.3kWh 1'i6 0.732 4,18 Subaru-VIVIO 10-mode 75km/17.5kWh 38.9 2.57 1.19 - EV 40km/h 141kin/kWh 73 1.37 2.24

Mazda 10-mode 43.3 2.31 1.32 Roadster(EV) 10-15mode 48.1 2.08 1.47

60km/h 69.8 1.43 2,14 60km/h 230km/3.g4k~ 16.A 6.21 0.495 Mazda-HR-X2(H2)

Daihatsu DASI-I21 (hforid) Mazda FCV

29 32 44

10-mode 10-15mode

3.13 3.45 2.27 40km/2.8Nm^3

0.98 0.889 1.35

Table B Energy Consumption and CO2 Emission per 100kin Driven

Resources

Crude Oil Natural Gas

Natural Gas

Natural Gas

Coal

Coal

...... Coal +m(co2=o)

Energy Consumption

Vehicle Type

Mining Driving Energy +Transp. Transform

(kg-CO2/lO0km)

TOTAL (k~-CO2 /lOOkm)

Gasoline V. 0,33 17.1 3.66 21.1 NG Vehicle 3.1 14.5 17.7

MeOH Vehicle 4.67 16.3 2.72 23.7

6.61 - 29.9 36.5

3.668 - 71.9 75.6

- 26.3 27.6

9.01 6.79

5.47kg-gasoline 5.25kg-NG

11.83kg-MeOH (7.68kg-NG) 1.674kg-H2

(10.87kg-NG) 1.674kg-H2 (28kg-Coal)

21.0kWh (10.3kg-coal) 6.18kg-coal

+ 1.233kg-I-I2

Hydrogen V (NG transform)

Hydrogen V (Electrolysis)

EV

CO2 Transform MeOH V + EV

1.348

0.86 16.7

40

30

W O w

" ' ~ 20

v 10

mDr iv ing

[3 Energy+Transform

D M i n ing+Transp

> > > > > .

- - o -,- ~-~ --~ m o z o z . o w O r,~

C~l I l l

Toh~ CO2 E ~ s s i o n per 100kin dr ive Fig.2

ii

lad -T- O + Q E