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Analysis to clarify the influence of diesel nozzle hole specifications on HC emission is performed by using a single cylinder engine. The total nozzle hole area and the number of holes are the investigation parameters. The experimental results show that HC emission under low-load condition becomes higher with not only the increase of the total nozzle hole area but also the decrease of it. The reason for the increase of HC emission with small hole area is that the longer spray tip penetration of the pilot injection accelerates the spray diffusion in the cylinder, and the over-lean fuel-air mixture areas become easily formed.

The third generation four valve lean combustion engine controlled by newly designed combustion pressure sensor has been developed. This combustion sensor composed of a metal diaphragm and a thin silicone layer formed on devitron piece detects the combustion pressure in the No.1 cylinder. Comparing with the lean mixture sensor equipped in the first and second generation lean combustion engine, the lean misfire limit was detected directly with this sensor, and the lean operation range was expanded, which realized lower fuel consumption and NOx emission. The output torque fluctuation was minimized by precisely compensating the fuel supplied to individual cylinder based on the crank angle sensor signal. Separated dual intake ports, one with the swirl control valve and the other with helical port shape was designed and a twin spray injection nozzle was equipped between those ports. The swirl ratio was lowered from 2.2 to 1.7.