Potential of HCCI for large natural gas fueled engines

摘要

High demands are placed on large gas engines in the areas of performance, fuel consumption and emissions. Future emission limits will make it necessary to develop new concepts to reduce emissions dramatically without decreasing efficiency or engine power. One way to reach this goal is to use catalysts (oxidation catalysts, SCR catalysts). The disadvantages of this method are the high costs of both the catalysts and the usage of additives to reduce nitrogen emissions. On the other hand, reduction of emissions should be possible by using new combustion concepts, such as Homogeneous Charge Compression Ignition (HCCI). Within this paper different ways to reach homogenous auto ignition with natural gas are shown. HCCI with pure natural gas was realized using very high compression ratios, high levels of EGR and high intake manifold temperatures. In addition, dual fuel systems have been investigated. Diesel has been used as second fuel with internal mixture and n-heptanes, gasoline and Diesel with external mixture formation. All the tests were carried out on a single cylinder research engine with a displacement of about 6.2 liters. The results of the investigations show the effects of different parameters (compression ratio, intake manifold temperature, EGR rate) on the combustion process and what engine power, efficiency and emission levels can be reached using HCCI.