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. Both the effects have been found to be significant. In particular, as for the former, the PCCI engine operated stably even at an air-fuel ratio of 80 when the temperature of the intake air was about 170 °C.FUTURE ENGINES should be both efficient and clean. High efficiency can be attained by high compression ratio and lean-burn. Diesel engines are a typical lean-burn engine with high compression ratio, and have the highest efficiency in the present reciprocating engines. However, diesel engines emit a large amount of NOx and soot due to the adoption of stratified charge combustion. This situation is also true of stratified charge spark ignition engines .In the oxygen-rich atmosphere, suppression of NOx formation in the cylinder is more effective for NOx reduction than NOx purification by current catalysts. Premixed lean-burn engines  have been expected for in-cylinder NOx reduction because combustion of premixed lean mixture produces much lower NOx compared with stratified charge combustion. Compared with diesel engines, premixed lean-burn spark ignition engines achieve somewhat low NOx emission but bad fuel economy because of limited stable combustion range. For extending the lean limit, multi-point ignition engines [3-4] which reduce the distance of the flame propagation are reported to be effective. As for other gasoline engines [5, 6 and 7], it is reported that stable operations are achieved only by multi-point self ignition under low speed and low load operating conditions. Either engine does not have high compression ratio, and then is inferior to diesel engines in fuel economy.Considering the above, an engine provided with premixed lean mixture, high compression ratio and multi-point spontaneous ignition is ideal for achieving both better fuel economy and lower NOx emission. Thus a Premixed-Charge Compression Ignition (PCCI) engine has been manufactured experimentally. The PCCI engine manufactured is a single cylinder engine with inlet port injection of gasoline.