21 Development of a Small Displacement Gasoline Direct Injection Engine

We have developed a small-displacement gasoline direct-injection engine (1.3L). Gasoline direct-injection engines rely on ultra-lean stratified combustion to deliver significantly better fuel economy, and are already used in many practical applications. When gasoline direct-injection is applied to a small-displacement engine, however, the amount of wall wetting of fuel on the piston surface will increase because the traveled length of the fuel spray is short. This may result in problems such as smoke production, high emissions of unburned HC, and poor combustion efficiency.

We solved these problems by forming an ideal air-fuel mixture distribution as follows: (1) by developing new multi-hole injectors (maximum fuel pressure of 12 MPa), which offer a high degree of freedom in arranging the fuel spray pattern, have superior atomization characteristics, and maintain their spray shape under high backpressure conditions; and (2) by developing the piston cavity and using a variable swirl control valve to optimize the air motion. These techniques have also made it possible to obtain stable stratified combustion throughout a wide operating range with reduced NOx emissions under a large EGR rate.