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Intake valve deposits (IVD) and combustion chamber deposits (CCD) in spark-ignition engines greatly affect nitrogen oxides (NOx) emission and octane requirement increases (ORI) as they prevent the heat release from the combustion chamber and increase the compression ratio. Currently, fuel performance additives to control IVD and CCD have been attracted and evaluation method based on CCD weight and thickness has been widely used. However, simple measurement of the CCD weight and thickness does not clearly reflect the CCD effect on the ORI, as the shape and location of the deposits are also crucial factors that must be considered along with the weight and thickness of the deposits. In this paper, an ORI engine test procedure using a 4 cylinder 2.0 liter SOHC engine is introduced.

A multizone phenomenological combustion model, in which the fuel bum rate is governed by the rate of fuel vaporization and mixing, is developed to study the effects of split injection schemes on NO and soot emissions of direct injection diesel engines. This model is calibrated with the experimental data of a single injection case. Comparison between the results calculated by the model and experimental results shows that the model has a good predictive capability for cylinder pressure, heat release rate, NO & soot emissions. The study of split injection parameters, including the delay dwell between injection pulses, the fuel quantity injected in the second pulse and the fuel pressure of the second injection, is carried out. The results predicted by the model show that the soot can be effectively reduced without increasing NO emission and fuel consumption with the split injection in which 10-30% of total fuel is injected in the second injection at about 15 °CA after top dead center.

The effect of various intake compositions and intake pressure on combustion & emission characteristics has been investigated in a single cylinder direct injection diesel engine. The variation of intake composition is simulated using argon, nitrogen and carbon dioxide as intake air diluents, and a screw compressor is used to boost intake pressure up to 200KPa. All diluents are found to be effective in reducing NOx emissions when intake pressure is changed from 110KPa to 200Kpa. Smoke emissions are drastically increased by the addition of argon, moderately increased by the addition of nitrogen. However, the addition of carbon dioxide substantially reduces smoke emissions and NOx emissions simultaneously. At lower intake pressure, the effects of diluting intake air with argon, nitrogen and carbon dioxide on ignition delay are proportional to their specific heats respectively, whereas the addition of argon has almost no effect on ignition delay when intake pressure is higher than 150KPa.