To secure preferable combustion even in a low speed region such as during idle operation, improve fuel consumption and prevent aggravation of condition of exhaust gas in a jump-spark ignition direct injection engine 1, in which fuel spray is guided around an ignition plug 16 by a wall surface of a cavity 5a provided in a crest plane of a piston 5 so as to be stratified.
A control unit A comprises a fuel pressure control section 50c which gradually raises fuel pressure in accordance with increase in rotational speed of the engine 1 basically when the engine is in a stratification combustion zone and which heightens injection pressure of fuel so as to compensate for decrease of the fuel atomization characteristic caused by weakening of flow in a cylinder in the low speed region of the stratification combustion zone. The control unit comprises an injection control section 50a which sets a fuel injection start timing at a retard angle side rather than BTDC 40 degrees CA so that the fuel spray can be securely trapped in the piston cavity 5a when the fuel pressure is increased in the low speed region. The control unit comprises an EGR control section 50b which controls an EGR valve 44 so that a recirculation rate of the exhaust gas may be substantially 40% or more in the low speed region.
FUJIKAWA TOMOHISA
TOSHINARI TAKASHI
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