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The effects of jet-jet angle on the combustion process were investigated in an optical accessible rapid compression and expansion machine (RCEM) under various injection conditions and intake oxygen concentrations. The RCEM was equipped with an asymmetric six-hole nozzle having jet-jet angles of 30° and 45°. High-speed OH* chemiluminescence imaging and direct photo imaging using the Mie scattering method captured the transient evolution of the spray flame, characterized by lift-off length and liquid length. The RCEM operated at 1200 rpm. The injection timing was -5°ATDC, and the in-cylinder pressure and temperature were 6.1 MPa and 780 K at the injection timing, respectively, which achieved a short ignition delay. The effects of injection pressure, nozzle hole diameter, and oxygen concentration were investigated.

Natural gas/diesel dual fuel engines have potential for a high thermal efficiency and low NOx emissions. However, they have the disadvantages of high unburned species emissions and lower thermal efficiencies at low loads (at low equivalence ratio). A way to solve this problem is to properly distribute the pilot fuel vapor in a natural-gas premixture. The combustion chamber geometry affects the combustion process since it influences the distribution of the pilot fuel vapor. This study investigates the influence of injection conditions and the piston bowl geometry on the performance and emissions of a dual fuel engine. Experiments were carried out using two pistons with different bowl diameters, 52 mm and 58 mm, at single-and two-stage diesel-fuel injection. The results show that the larger bowl provides lower hydrocarbon emissions at a lower equivalence ratio in the case of single-stage injection.

The main objective of this study is to evaluate the characteristics of combustion that combine premixed charge compression ignition (PCCI)-based combustion with conventional mixing controlled combustion. In this type of combustion, it is supposed that the combustion duration is shortened due to the synchronization of the timing of two types of combustions. In addition, the cooling loss caused by spray impingement is expected to decrease by the reduction of the proportion of mixing controlled combustion. In this study, the effect of injection pressure, injection timing, and split injection on thermal efficiency and emissions were investigated in order to determine the appropriate injection parameters for PCCI-based combustion to realize the proposed combustion concept.

A series of experiments was conducted using a single-cylinder small-bore (85 mm) diesel engine to investigate the smoke-reduction effect of post injection by varying the number of injection nozzle orifices and the injection pressure. The experiments were performed under a constant injection quantity condition and under a fixed NOx emission condition. The results indicated that the smoke emission of six-hole, seven-hole, and eight-hole nozzles decreased for advanced post injection, except that the smoke emission of the 10-hole nozzle increased as the post injection was advanced from a moderately late timing around 17° ATDC. However, the smoke emission of the 10-hole nozzle with a higher injection pressure decreased for advanced post injection. These trends were explained considering the influence of the main-spray flames on post sprays based on CFD simulation results.

The aim of this study is to find strategies for fully utilizing the advantage of diesel-ethanol blend fuel in recent diesel engines. For this purpose, experiments were performed using a single-cylinder direct injection diesel engine equipped with a high-pressure common rail injection and a cold EGR system. The results indicate that significant PM reduction at high engine loads can be achieved using 15% ethanol-diesel blend fuel. Increasing injection pressure promotes PM reduction. However, poor ignitability of ethanol blended fuel results in higher rate of pressure rise at high engine loads and unstable and incomplete combustion at lower engine loads. Using pilot injection with proper amount and timing solves above problems. NOx increase due to the high injection pressure can be controlled employing cold EGR. Weak sooting tendency of ethanol-blend fuel enables to use high EGR rates for significant NOx reduction.

To improve performance and exhaust emissions of a converted dual-fuel natural-gas engine, the effects of basic parameters were experimentally investigated. The results show that diesel fuel operation is favorable at very low loads and that a small amount of pilot fuel with a moderate injection rate is effective for suppressing knock at high loads. As for the charge air throttling, there is an optimal combination of charge amount and equivalence ratio to obtain high thermal efficiency and reduced emissions. An optimal strategy for fueling is demonstrated based on the results. Adequate control of pilot fuel amount, injection timing and throttle opening area gives diesel-equivalent thermal efficiency with very low smoke emission over a wide range of loads.

To find more effective lean mixture preparation methods for smokeless and low NOx combustion, a numerical study of the effects of in-cylinder flow field before injection on mixture formation in a premixed compression ignition engine was conducted. Premixed compression ignition combustion is a very attractive method to reduce both NOx and soot emissions, but it still has some problems, such as high HC and CO emissions. In case of early direct injection, it is important to avoid wall wetting by spray impingement, which can cause higher HC and CO emissions. Since it is not easy to examine the effects of initial flow and injection parameters on mixture formation over the wide range by practical engine tests, a computer program named “GTT (Generalized Tank and Tube)” code was used to simulate the in-cylinder phenomena before autoignition.