| 摘要 |
PROBLEM TO BE SOLVED: To improve ignition ability and stabilizes combustion so that thick air-fuel mixture always exists near an ignition plug without being affected by fuel injection timing during a lean burn operation. SOLUTION: It is determined whether a region is a region for performing the lean burn operation or not (S101). When it is the region for performing the lean burn operation, and injector's injection period required for injecting a fuel amount per one process required for realizing a desired air-fuel ratio in the lean burn operation region under a fuel pressure adjusted by a pressure regulator for low pressure is calculated (S103), and the fuel pressure is adjusted to the low pressure side (S104). Thus, an injection period is extended when a fuel amount in one cycle in the lean burn operation region is injected from the injector, thick air-fuel mixture always exists near an electrode part of the ignition plug without being affected by fuel injection timing, the ignition ability is improved, and the combustion is stabilized.
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