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The objective of the present study is to elucidate the combustion process of partial premixed charge compression ignition (PCCI) combustion using multiple injections in diesel engines. The effects of the ratio of the quantity of fuel used in the first and second injections, and the injection dwell time on heat release rate, soot and nitrogen oxide (NOx) formations are investigated in simulated partial PCCI combustion using a constant-volume vessel. N-heptane is used as fuel. The experiments are carried out under an ambient condition of 2 MPa and 900 K, which simulates a PCCI-like heat release rate with long ignition delays. The oxygen concentration is set to 21 and 15% to simulate conditions without and with exhaust-gas recirculation (EGR), respectively. The fuel quantity in the first injection is varied between 10 to 40% of the total fuel quantity, and the injection dwell is varied between 0.5 to 2.0 ms.

This study aimed to elucidate the ignition processes in transient fuel-sprays over a wide range of ambient conditions corresponding to PCCI combustion, as well as diesel combustion. Ignition of n-heptane sprays was experimentally investigated by using a constant-volume vessel. The well-known temperature dependencies of ignition delays were observed at a high ambient pressure. On the other hand, a negative temperature coefficient (NTC) accompanying a two-stage pressure rise was detected for lower ambient pressures. High-speed shadowgraph images indicated that the temperature rise begins in the highly homogenous mixture along the combustion chamber wall. Enhancement of fuel-air mixing with elevated injection pressure and a reduced nozzle orifice delays the appearance of hot flame in the NTC condition. To better understand these phenomena, ignition processes were predicted using an ignition model including a stochastic turbulent mixing model and a reduced chemical reaction scheme.

The effects of fuel injection conditions (injection pressure, nozzle orifice diameter and fuel injection quantity) on NOx formation in direct-injection Premixed Charge Compression Ignition (DI-PCCI) combustion were investigated using a constant-volume vessel and a total gas-sampling device. The results show that promotion of fuel-air mixing reduces final NOx mass accompanying a delayed hot flame. In particular, under low oxygen mole fraction conditions, in addition to the hot flame delay, the promotion of fuel-air mixing results in a lower heat release rate. In this case, the final NOx mass is further reduced. For a fixed nozzle orifice diameter, the final NOx mass is reduced with increasing injection pressure. This effect is remarkable for smaller nozzle orifice diameters. Regardless of the oxygen mole fraction, under the low injection fuel quantity condition, enhancement of fuel-air mixing reduces the final NOx mass per released heat.

The combustion process of natural gas in a premixed charged compression ignition (PCCI) engine is analyzed using computational fluid dynamics via stochastic approach. The nonuniform states of turbulent mixing and the ignition process are statistically described using probability density function (PDF). The results show that the course of in-cylinder pressure is good agreement with experimental data, and the effect of mixture heterogeneity on the ignition delay and the rate of heat release is revealed.

The Premixed Charge Compression Ignition (PCCI) natural-gas engine has been investigated extensively as a power source for stationary applications due to its potential for high thermal efficiency and very low NOx emissions. However, methane, which is a major component of natural gas, has a high auto-ignition temperature. Stable ignition of natural gas in PCCI engines can be achieved by high compression ratio, intake air heating, internal EGR and various other techniques. Although each of the above-mentioned methods shows positive effects, to some extent, on engine performance and emissions, the literature indicates that stable operation of the PCCI natural gas engine would require a combination of various techniques, which reveals the need for further investigation. The goal of the present study is to control the PCCI natural gas ignition and combustion by ozone addition into the intake air.

Utilization of ethanol-diesel blend fuels in partial Premixed Charge Compression Ignition (PCCI) combustion was attempted to achieve clean diesel engine. The experiment was carried out using a naturally aspirated single cylinder DI diesel engine equipped with common rail injection and cooled EGR systems. PCCI combustion was realized by two stage injection in which part of fuel was injected during the compression stroke and the rest near TDC. The results indicate that under middle to high engine loads, both weak sooting tendency and low cetane number of ethanol blend fuels offer a great improvement in PM and NOx emissions when compared to the diesel combustion with ordinary pilot injection. However, this results in penalties in thermal efficiency, THC and CO emissions.

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.