The Clean Engine Vehicle Project

		A joint project between Empa (Internal Combustion Engines Laboratory) and ETH (Aerothermochemistry and Combustion Systems Laboratory and Measurement and Control Laboratory).

Natural gas and biogas are counted among the cleanest fuels. Modern natural gas vehicles emit less pollutants as gasoline or diesel driven vehicles and also the effect based assessment of the exhaust emissions is better: the ozone forming potential of the hydrocarbon fraction is much lower, the content on carcinogenic components as benzene, 1.3-butadiene, formaldehyde or acetaldehyde is nearly not measurable and the particulate emissions are near zero. Natural gas vehicles have additionally a big potential for a CO2 reduction. Alone, based on the lower content of carbon in the fuel, the CO2 reduction of a natural gas driven vehicle is about 20%, compared with a gasoline vehicle. Based on the high knock resistance of natural gas, advanced dedicated natural gas vehicles can be optimized regarding higher energy efficiency. Such vehicles have the potential for a CO2 reduction of 30%. With the project “Clean Engine Vehicle”, Empa and ETH demonstrated the potential of such an optimized natural gas vehicle regarding pollutants and CO2 reduction with todays engine technology. Within the project, an actual gasoline driven engine was converted to dedicated natural gas operation, the compression ratio has been optimized, a catalytic converter was developed and a downsizing concept (supercharging with boost control and gear box modifications) was realized. Aim of the project was a CO2-reduction of 30% in the official European driving cycle compared with a similar powered gasoline vehicle and the compliance with the most stringent European and Californian exhaust gas limits for Euro-4 and Super-Ultra-Low-Emission-Vehicles (SULEV).

Fig. 1		The pollutants could be reduced below the targeted limits (Fig. 1). The NOx concentrations were after a driving distance of about 300 m after cold start even in transient driving always lower at tailpipe then in the intake air of the engine (Fig. 2).

Fig. 2		Compared with a gasoline engine with similar performance, the CO2 emissions could be reduced at 31% (Fig 3). The most important CO2 reduction of 22% could be realised by the conversion to natural gas operation and is based on the lower carbon content of natural gas compared with gasoline.

Fig. 3

Simultaneously, the maximum engine power was reduced at about 15% by the gas induced reduction of engine filling. The increase of compression ratio resulted in a further CO2 reduction of 2.7% and the maximum engine power could be increased by 6.5%. The supercharging and gearbox modifications reduced the CO2 emissions again by 3.4% and increased the maximum engine power by 33%. With all this measures, the maximum engine power was increased by 20% compared with the basic 1.0 l gasoline engine.