The Experimental Investigation On Combustion And Emissions Of Low-Temperature Combustion Of Diesel Engines

Low temperature combustion is a hot research topic of diesel combustion process, which has the potential to meet stringent emission legislation, and combustion control optimization is the key point to realize high efficiency clean combustion. Firstly, this paper systemically investigated the effects of EGR rate, injection parameters, combustion phase and oxygenated additive on the combustion and emission characteristics of diesel low temperature combustion; then further test was conducted to investigate the effects of EGR rate on the main components of diesel pollutant emissions.At first, experimental study was conducted to investigate the effects of injection parameters, EGR rate, combustion phase and oxygenated additive on combustion and emissions of diesel low temperature combustion. Test results showed that, it is an effective measure to improve the combustion process and reduce emissions by increasing injection pressure, especially under massive EGR rate conditions; NOx can be effectively reduced by applying EGR, soot firstly increases than decreases with increased EGR rate, however, over high EGR rate results in dramatically increase of THC and CO emissions, as well as deteriorated fuel economy; Much lower NOx emission can be achieved by optimized combustion phase control while still maintaining good fuel economy, however, early combustion phase leads to much higher pressure rise rate, therefore it needs to be carefully calibrated during the combustion control optimization process; There are not too much effects of post injection on soot, CO and THC under high EGR rate conditions, thus further investigation is still needed to be carried out which concerning on the mechanism of post injection under low temperature combustion; Soot reduction can be obtained by blending oxygenated additive into diesel fuel, especially under massive EGR rage conditions. This could provide a reference to realize high efficiency, clean low temperature combustion from the perspective of fuel characteristics. Then test was carried out to study the effects of EGR rate on the variations of NOx component, CH₄ component in THC and PM component in diesel pollutant emissions. Results showed that, the proportions of both NO2 and N2O first increase than decrease with the increase of EGR rate, and reach their peak values when EGR rate is around 55%, both are much higher than low EGR rate conditions; The CH₄ component in THC emission also increases with increased EGR rate (can be more than 15% if EGR rate reaches up to 60%). In certain EGR rate range, both THC emission and CH4 component in THC can be reduced by increasing injection pressure. The PM test result showed that EGR rate poses a very important role on the particle diameter and number.