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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 by the standard emission equipment. Unregulated emissions such as aldehydes and ketones were measured by high pressure liquid chromatography and hydrocarbon speciation by gas chromatography. Particulate mass was measured with a Tapered Element Oscillating Microbalance (TEOM). 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.

I The effect of Cetane Number (CN) of the fuel and the addition of cetane improvers on the cold starting and white smoke emissions of a diesel engine was investigated. Tests were conducted on a single-cylinder, four-stroke-cycle, air-cooled, direct-injection, stand-alone diesel engine in a cold room at ambient temperatures ranging from 25 °C to - 5 °C. Five fuels were used. The base fuel has a CN of 49.2. The CN of the base fuel was lowered to 38.7 and 30.8 by adding different amounts of aromatic hydrocarbons. Iso-octyl nitrate is added to the high aromatic fuels in order to increase their CN to 48.6 and 38.9 respectively. Comparisons are made between the five fuels to determine the effect of CN and the additive on cylinder peak pressure, heat release rate, cold start-ability, combustion instability, hydrocarbon emissions and solid and liquid particulates.

Engine-out HC emissions were investigated during cold and hot starts. The tests were conducted at room temperature, on a new Chrysler 2.4-L, 4-cylinder, 16-valve, DOHC, multipoint-port-fuel-injection gasoline engine. Real time engine-out HC emissions were measured using Cambustion Fast Response Flame Ionization Detector (FRFID). Sources of unburned hydrocarbon emissions were discussed in details. Unburned hydrocarbons emitted during the cold-start were much higher than the hot-start. Cylinder-to-cylinder variation was investigated. A fuel inventory program was used to characterize total injected fuel, burned fuel, unburned HC, and fuel unaccounted for (mainly accumulated fuel in the engine system and CO). A fuel interrupt test was run to examine the possibility of burning the leftover fuel after the fuel shut-off. The contribution of the cold and hot start modes in engine-out HC emissions was determined.