抄録
A key word to combustion control with gasoline direct injection, is "freedom of mixing", that is, no restriction on mixture preparation. One of combustion control technologies utilizing the freedom of mixing, is "two-stage combustion" for quick catalyst warm-up. It is a kind of two-stage injection, with a main injection in a late stage of the compression stroke for stratified-charge combustion, and a supplementary injection in a late stage of the expansion stroke into the burned gas, for an increase in the exhaust-gas temperature. It is an important technology for a gasoline direct injection engine to promise to meet the stringent emission regulations. Unfortunately, however, it inflicts a loss of the fuel economy, because a part of fuel is consumed not to generate the torque, but to increase the exhaust-gas temperature. It is necessary to enhance its effectiveness, and cut its operation time. A characteristic mechanism of in-cylinder combustion is "time-domain mixing". This means that in the cylinder filled with a large number of eddies, together with inhomogeneity, products in different stages of combustion process have a chance to be generated at the same time, and the products in the past, the present, and the future along by the process, is mixed up by the eddies. The successful mechanism of the two-stage combustion is controlled by the time-domain mixing. A chamber-type exhaust manifold shown in Fig. 1, is a successful technology of inducing a kind of time-domain mixing in it, and enhancing the effectiveness of the two-stage combustion. A part of exhaust gas out of a cylinder is mixed with the blow-down gas out of the following cylinder, in it. As a result of enhanced reaction in it, HC emissions are reduced, and the exhaust-gas temperature is increased, as shown in Fig. 2. The operation time of the two-stage combustion is shortened, so that the fuel economy is improved by around 0.8 % on the EURO-3 mode.
