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An author's previous studies addressed a combustion system which reduces emissions, noise, and fuel consumption by using PCCI with the split injection of fuel. This concept relies on the premixed combustion of the first injected fuel and accelerated oxidation by the second injected fuel. Although this combustion system requires the optimization of the timing of the second injection, the details of how noise and emissions are reduced have not been elucidated. In this paper, the authors explain the mechanism whereby emissions and noise are reduced by the second injection. In-cylinder visualizations and numerical simulations both showed an increase in smoke and CO as the second injection timing was advanced, as induced by the inhibited oxidation of the rich flame. When the second injection timing is excessively retarded, the amount of soot forming around the near-nozzle increased.

Combustion of premixed lean mixture which arises from multi-point ignition is very promising and necessary for achieving both higher efficiency and lower nitrogen oxide (NOx) emission. A Premixed-Charge Compression Ignition (PCCI) engine has been manufactured experimentally and evaluated in terms of fuel economy and NOx reduction. The PCCI engine manufactured is a single cylinder engine with inlet port injection of gasoline, and has a compression ratio of 17.4. The PCCI engine operates stably in the air-fuel ratio range of 33-44. In the PCCI engine, spontaneous ignition occurs at unspecified points as it does in diesel engines. The flame then develops rapidly throughout the combustion chamber. Under conditions of stable combustion, the PCCI engine achieves equivalent fuel economy and much lower NOx emission compared with diesel engines. Furthermore, the effects of intake air heating and supercharging on extending the range of stable combustion have been examined.