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In this study, it was attempted to operate the 4-cycle multi cylinder natural gas engine introduced PCCI combustion system without electric heater for intake air heating. In experiment, by optimization of the compression ratio and in addition to the control of spark ignition timing, the engine could be operated using only intake air heating with coolant water. The results showed that the suppression of the auto-ignition timing variations among cylinders owing to the independent spark timing control of each cylinder leads to the improvement of engine output, fuel economy and exhaust emissions. Furthermore, this paper describes the engine starting and corresponding change of engine load on electric demand on generator. The stable operation could be achieved by using spark ignition, controlling of excess air ratio and intake air temperature during change the engine load from idle to rated power.

A novel EGR (exhaust gas recirculation) method by means of the intake-valve pilot-opening has been demonstrated using a single-cylinder test engine, in order to control the combustion and to reduce the energy loss due to intake-gas pre-heating in a natural gas HCCI (homogeneous charge compression ignition) engine. The intake valve, together with the exhaust valve, is slightly opened at the beginning of the exhaust stroke. Then, part of the burnt gas, which has a high temperature, is introduced into the suction pipe backward, resulting in an increase in the intake-gas temperature. The EGR rate can be varied successfully up to about 40% by using the specially designed camshaft and the valve control device, which can delay the closing timing. The effect of the EGR rate on engine performance and emissions has been investigated under the condition that the temperature of the fresh mixture and the fuel consumption rate are kept constant.

Utilizing the desirable feature of hydrogen, this study demonstrates the improvement of engine performance and exhaust emissions due to the mixing of hydrogen into natural-gas fuel in a spark-ignition engine at the wide-open throttle (WOT) condition. Both hydrogen and natural-gas fuels were injected into the intake port only in the suction flow, which could make the operation under a wide range of conditions without backfire even at a hydrogen fuel. Based on the measured processes of combustion, the knock characteristics were discussed with special attention to the extremely high burning velocity of hydrogen. At a higher compression ratio, the thermal efficiency in the stoichiometric condition was improved, nevertheless a precise control of ignition timing was required to suppress a hard knock. From the experimental results of engine performance in a variety of parameters, optimal use of hydrogen was exhibited for different engine loads.