The Addition of Hydrogen on the Combustion and Emission Characteristics of Natural Gas Fueled Vehicles

摘要

Automobiles have become an essential part of our economy and provide a convenience that most have become more dependent on, however they have also had a dramatic impact on our health and environment. Internal combustion engine fuelled by alternative fuels can efficiently decrease emissions while maintain high combustion efficiency. As a result there is incentive to find ways to use alternative fuels on vehicles. Compressed natural gas is a widely used fuel in the world for its low emission characteristics. However because of its lower combustion speed, the spark ignition engine fuelled by it can not meet more and more strictly emission limits. The laminar speed of Hydrogen is about 5 times of that of compressed natural gas, so it seems that the addition of some fraction of hydrogen into compressed natural gas will increase the combustion speed. This research involves studying the effect of adding different small fraction of hydrogen into a compressed natural gas spark ignition engine. Using online mixing system of natural gas and hydrogen developed by our team, an inline single point injection six-cylinder spark ignition engine was used to study the effect of different fraction of hydrogen on the combustion characteristic and emission level of it. The fraction of hydrogen is from 0% to 50%. It was found that the addition of hydrogen can shorten the combustion duration and increase the combustion speed. The addition of hydrogen can extend the lean burning limit of natural gas engine. As the addition fraction of hydrogen increases,the emission level of Nox will increase because of its high combustion temperature. Therefore the MBT timing of the engine should be retarded to obtain satisfied emission results. With leaner combustion limit and with retarded spark advance, the spark ignition engine fuelled with natural gas and hydrogen mixture can meet the emission need for Euro IV and has potential for satisfying Euro V. As the addition fraction of hydrogen increases,the indication efficiency will be improved a little.