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A new diffusing-oriented spray stratified combustion system for direct injection gasoline engines is proposed in this study. A reflector with multi-impingement wall head attached ahead of multi-hole injector nozzle is used in this system as a strategy of breaking up the fuel spray and directing it in a desired direction to form a perfect atomization and stratification of fuel air mixture. A comparatively rich fuel-air mixture is always formed over a wide range of engine operation conditions in the vicinity of spark plug due to the fuel spray oriented by the special surface shape of impingement wall, and the finely atomized fuel spray is formed in the other areas of combustion chamber due to the impacting of fuel spray against the impingement wall. Therefore, it is possible to achieve stable and fast burn of lean fuel air mixture. The combustion system is preliminary investigated on a single cylinder four-stroke DI gasoline engine which is shifted from a DI diesel engine.

Diesel engines offer better fuel economy compared to their gasoline counterpart, but simultaneous control of NOx and particulates is very challenging. The blended 2-way SCR/DPF is recently emerging as a compact and cost-effective technology to reduce NOx and particulates from diesel exhaust using a single aftertreatment device. By coating SCR catalysts on and inside the walls of the conventional wall-flow filter, the 2-way SCR/DPF eliminates the volume and mass of the conventional SCR device. Compared with the conventional diesel aftertreatment system with a SCR and a DPF, the 2-way SCR/DPF technology offers the potential of significant cost saving and packaging flexibility. In this study, an engine dynamometer test cell was set up to repeatedly load and regenerate the SCR/DPF devices to mimic catalyst aging experienced during periodic high-temperature soot regenerations in the real world.

Diesel particle filters (DPF) have become the standard and essential aftertreatment components for all on-road diesel engines used in the US and Europe. The OBD requirements for DPF are becoming rigorously strict starting from 2015 model year. The pressure sensor or other strategies currently used for DPF diagnostics will most likely become insufficient to meet the new OBD requirements and a post DPF soot sensor might be necessary. This means that it will be even more imperative to develop a DPF design that would not have any soot leaks in its emission lifetime, otherwise the DPF will become a high warranty item.

Heat transfer losses in the swirl chamber, throttling losses at the connecting passage and combustion delay in the main chamber are considered as the three factors influencing the thermal efficiency of IDI diesel engines. This paper suggests a thermodynamic model, in which three idealized diesel engines including no passage throttling engine, adiabatic diesel engine for swirl chamber and DI diesel engine are assumed, to isolate heat transfer losses, throttling losses and combustion delay in IDI diesel engines. The Second Law analysis is carried out by the thermodynamic state parameters calculated by the cycle simulation of engines based on the First Law. The effects of heat transfer losses in the swirl chamber, throttling losses at the connecting passage and combustion delay in the main chamber on the irreversibilities and availability losses during the engine cycle are analysed in detail. The relative influences among the three losses are also investigated.

The configuration of intake and exhaust manifolds has a strong impact on the gas exchange process of reciprocating engines. To make the designer assess a large number of manifold configurations quickly, a frequency analysis technique is developed, which is based on one-dimensional wave action equations. The frequency spectra of gas pressure pulsation in manifolds with different cylinder number, different manifold layouts and different manifold parameters are calculated, and the effects of various parameters on the spectrum characteristics are studied. The relationship between predicted frequency spectrum and measured volumetric efficiency is investigated for engines with different cylinder number. The experimental results for engines with different cylinder number show that this technique can be used to select the manifold parameters required in the initial stage of design and can save much CPU time compared to a siumlation program based on the method of characteristics.

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.

The effect of combustion chamber wall-wetting on the emissions of unburned and partially-burned hydrocarbons (HCs) from gasoline-fueled SI engines was investigated experimentally. A spark-plug mounted directional injection probe was developed to study the fate of liquid fuel which impinges on different surfaces of the combustion chamber, and to quantify its contribution to the HC emissions from direct-injected (DI) and port-fuel injected (PFI) engines. With this probe, a controlled amount of liquid fuel was deposited on a given location within the combustion chamber at a desired crank angle while the engine was operated on pre-mixed LPG. Thus, with this technique, the HC emissions due to in-cylinder wall wetting were studied independently of all other HC sources. Results from these tests show that the location where liquid fuel impinges on the combustion chamber has a very important effect on the resulting HC emissions.

A recently developed in-cylinder fuel injection probe was used to deposit a small amount of liquid fuel on various surfaces within the combustion chamber of a 4-valve engine that was operating predominately on liquefied petroleum gas (LPG). A fast flame ionization detector (FFID) was used to examine the engine-out emissions of unburned and partially-burned hydrocarbons (HCs). Injector shut-off was used to examine the rate of liquid fuel evaporation. The purpose of these experiments was to provide insights into the HC formation mechanism due to in-cylinder wall wetting. The variables investigated were the effects of engine operating conditions, coolant temperature, in-cylinder wetting location, and the amount of liquid wall wetting. The results of the steady state tests show that in-cylinder wall wetting is an important source of HC emissions both at idle and at a part load, cruise-type condition. The effects of wetting location present the same trend for idle and part load conditions.