Direct Numerical Simulations of Low Temperature Combustion in IC Engine Related Conditions

Sammanfattning: Popular Abstract in English Internal combustion engine plays an important role in our society. In our daily life, we use them to drive cars, trucks, ships, generating electricity and heat, and in many other applications. Modern internal combustion engines fall into three catalogues: gasoline engines, diesel engines and low temperature compression ignition engine. They are developed to achieve higher efficiency to prolong the use of fossil fuels that have a limited reserve on earth, and to reduce carbon dioxide emission per kilometre of drive. Our public concern on environment has promoted more stringent environment legislations that demand internal combustion engines to run with low emissions (carbon monoxide, NOx, unburned hydrocarbons, and particulate matters). In the past two decades, advanced low temperature combustion (LTC) engines, including HCCI (homogeneous charge compression ignition), SACI (spark assisted homogeneous charge compression ignition), PPC (partially premixed charge compression ignition) engines, have been under intensive research and development. These engines operate at low temperatures and high compression ratios to minimize pollutant emissions and to achieve high efficiency. Engine experiments have been performed in many university laboratories and internal combustion engine industry and the advantages of the LTC concept have been fully demonstrated. However, to put these low temperature combustion engines into mass production, several issues need to be resolved. Extensive experiments showed that LTC engines tend to have high engine noise and difficulty of combustion controlling. Therefore, different strategies need to be developed to overcome various technological barriers. This thesis is aimed at gaining theoretical understanding of the fundamental chemical and physical processes in LTC engines. This is done by carrying out direct numerical simulation (DNS) of the combustion process employing high accuracy numerical algorithms and the full set of partial differential equations that govern the physical and chemical process. In DNS all the detailed temporal evolution and spatial structures of ignition and chemical reaction zones occurring in LTC engines are computed. The results of DNS reveal several important characteristics of LTC engines. The locations and reasons of the emissions of carbon monoxide, NOx, unburned hydrocarbons in LTC are identified. The origin of the high noise is identified. It is demonstrated that by optimizing the fuel injections one can achieve a compromise among carbon monoxide, NOx,unburned hydrocarbons emissions.