Abstract
HCCI engines can operate with high thermal efficiency and significant low NOx emission. A new engine concept consists of HCCI combustion in low and middle load and spark ignition combustion in high load was introduced (Fig. 1). Conditions for HCCI was considered to adjust the negative valve overlap and effective compression ratio by intake valve close timing. And also, we investigated the influence of the mixture formation on auto-ignition using a direct injection engine. Fig.2 shows how to control ignition and combustion. As the result, HCCI combustion was achieved with relatively low compression ratio combined with an intake air heat by internal EGR. High thermal efficiency comparable to those of modern diesel engine, almost zero NOx emission and no smoke were realized. The mixture stratification increases the local concentration resulting in higher reactivity. The wide range of combustible A/F ratios explosion enables control of ignition timing of compression ignition. Combustion photographs indicate how the flame fills the entire combustion chamber to produce combustion, and to reduce emissions and fuel consumption.
