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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.

Engine misfire (total or partial) causes a negative effect on the engine power and the exhaust emissions such as HC, CO and NOx. Moreover, it causes damage to the three-way-catalyst(TWC) system permanently. So, Engine misfire should be detected and eliminated. This study introduces a new system concept which is detecting combustion misfire using breakdown voltage (BDV) characteristics between electrodes. The focus of this study is that the detection and decision of misfire criterion through the misfire intensity calculation with BDV signal, which is derived by the application of a high bias voltage (30kV) to the spark-plug gap in the engine continuously. This study is driven to check the relation among BDV signal and misfire intensity inside an engine cylinder.

Recent advanced technologies in diesel engine FIE(Fuel Injection Equipment) allow high pressure and multiple injection to be used to reduce particulate emissions without significant penalty in NOx emission. It is also well known that diesel engine particulate matter(PM) and NOx emissions can be reduced by the exact injection rate control according to engine conditions. This study was conducted based on such engine conditions as engine speed, load, swirl ratio and solenoid pulse timing and duration. The fast solenoid valve was installed between the connecting part of nozzle and fuel line. The ball valve driven by solenoid is open after the controller generates pulse and it spills the high pressure fuel in the high pressure nozzle chamber. Fuel line pressure, injection rate, cylinder pressure and exhaust emissions were measured with the variation of control method(pulse timing and pulse duration period).