Abstract
In this paper, the potential of combined injection of CNG and gasoline is studied on a 1.7 L turbocharged, port-injected SI engine and the best engine performance point for the best conversion efficiency of the catalytic converters has been investigated. Compressed natural gas (CNG) as an alternative fuel is used in spark ignition engines to improve fuel consumption and exhaust emissions. The improvements gave more advantage in emission but it lowered the performance of the engine. As a substitute, CNG has a higher octane number and knocking resistance than gasoline and hence CNG-dedicated engines can have higher compression ratios and therefore higher indicated efficiencies. Turbocharged bi-fuel, combined CNG and gasoline, injection engine of is a new concept which offers direct benefits with regards to gas or gasoline powered vehicles running separately on each fuels. It also opens very interesting perspectives for meeting future emission regulations using only a three-way catalyst, since the stoichiometry condition of combustion is maintained over the whole engine operating range. Results show that the combined injection of gasoline and CNG is much better than gasoline mode in terms of fuel consumption and raw HC and CO emissions. However, as expected the NOx emission will increase. According to the obtained results at 16.2 bar BMEP, 3000 rpm full load condition with 30% CNG mass fraction, the BSFC, CO and HC emissions are improved by 16, 66 and 50%, respectively, compared to gasoline single mode. It was found that a fuel mixture of 30% CNG mass fraction was the best trade-off point between engine performance and emission production. Also, significant reductions of fuel consumption were observed. Full-load tests carried out with a turbocharged engine enhanced the synergy effect between the two fuels at full-load condition.
Highlights
Compressed natural gas (CNG) is an alternative fuel, which can be used as a replacement for gasoline, diesel, or propane fuel
This study investigates the potential of combined injection as compared to the gasoline and CNG operation to find the best point of trade-off between performance and emissions, which is the state of the art in this field of research
The synergy effect of combination of CNG with gasoline was investigated on a 1.7 L port injection turbocharged engine
Summary
Compressed natural gas (CNG) is an alternative fuel, which can be used as a replacement for gasoline, diesel, or propane fuel. Pipitone and Beccari [7] investigated the effects of combined injection of gasoline and CNG in a naturally aspirated spark ignition engine with injection of gasoline and CNG in the intake manifold They studied the knock tendency of the mixed fuel and concluded that it is lower than for gasoline and the spark timing is less retarded. Obiols et al [9] investigated the effects of gasoline and CNG mixed injection in a turbocharged spark ignition engine with direct injection of gasoline inside cylinders and port injection of CNG in the intake manifold They strengthened valve seats for erosion prevention at high thermal loads. Recent research proves that concomitant injection of gas and liquid fuel in SI engines can lead to strong synergies between the two fuels In these studies the main focus has been on performance, torque and thermal efficiencies of the engines. This study investigates the potential of combined injection as compared to the gasoline and CNG operation to find the best point of trade-off between performance and emissions, which is the state of the art in this field of research
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