An analysis of sources of regulated and unregulated emissions from a single cylinder HSDI engine in low temperature combustion regime

Due to the high efficiency and fuel economy, small bore, high speed, direct injection diesel engines are growing in popularity to power light duty vehicles these days. In spite of their high efficiency engine manufacturers are under increasing regulatory pressure to reduce the emissions further to meet future standards. Engine-out emissions can be reduced by optimizing engine design and operating parameters. But reducing emissions using in-cylinder processes is tricky as the different physical and chemical processes are interconnected. A change in one input variable leads to changes in several output variables. The combined effects of the design and operating parameters are further complicated by the small-bore combustion chamber of the HSDI engine.; There is a need for interpretation of the results to obtain simpler concepts which can be applied by an engineer in industrial challenges during the development of diesel engine.; Therefore the study aims at developing simple concepts to understand the complex processes of the diesel combustion and use them to analyze the effect of the key operating parameters, and their combinations on regulated and unregulated engine-out emissions and their sources of formation in a small bore, HSDI diesel engine in the low temperature regime which has been gaining widespread popularity.; Several mechanisms are discussed to understand the formation of both regulated and unregulated emissions in a high speed, direct injection, single cylinder diesel engine using low sulphur diesel fuel. Experiments were conducted over a wide range of injection pressures, EGR rates, injection timings and swirl ratios. The regulated emissions were measured using standard emission equipment. Unregulated emissions such as aldehydes and ketones were measured by high-pressure liquid chromatography and hydrocarbon speciation by gas chromatography. Analysis was made of the sources of different emission species and their relationship with the combustion process under the different operating conditions. Special attention is given to the low temperature combustion (LTC) regime, which is known to reduce both NOx and soot. However the HC, CO and unregulated emissions increased at a higher rate.; Also, several mechanisms are discussed to understand the particulate matter (PM) characterization. This includes their formation, size distribution and number density. Experiments were conducted over a wide range of injection pressures, EGR rates, injection timings and swirl ratios, therefore covering both conventional and low temperature combustion regimes. A micro dilution tunnel was used to immediately dilute a small part of the exhaust gases by hot air. A Scanning Mobility Particle Sizer (SMPS) was used to measure the particulate size distribution and number density. Particulate mass was measured with a Tapered Element Oscillating Microbalance (TEOM). Analysis was made of the root cause of PM characterization and their relationship with the combustion process under different operating conditions. PM increased with an increase in EGR in conventional combustion regime and decreased with increase in EGR under the Low Temperature Combustion (LTC) regime. The size distribution and number density shows more complex trends. The particulate formation was broadly divided into nucleation and accumulation modes and their relative roles contributing to the final PM characterization are discussed.