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This study proposes a new combustion chamber concept for small DI diesel engines. Reduction of fuel adhering to the cavity wall, improvements in mixture formation, and an optimum distribution of mixture inside and outside the cavity are the main characteristics of the combustion chamber. The spray formation and it's distribution inside and outside the combustion chamber was investigated photographically in a small DI diesel engine with transparent cylinder and piston. Optimization of the fuel spray distribution inside and outside the cavity was attempted by changing the shape of the cavity entrance and the location where spray impinges on the lip. In addition improvements in the mixture formation of the impinging spray and reductions in the fuel adhering to the cavity wall were attempted by introducing a small step on the cavity side wall. The results were confirmed by analyzing the combustion and emission in an actual DI diesel engine.

Nitrous oxide (N₂O) emission reduction has gained large prominence recently due to its contribution to the climate change as a greenhouse gas. The United States Environment Protection Agency (US-EPA) together with the United States Department of Transport (DOT) has already regulated the N₂O emissions from light-duty vehicles (LDV) to 0.010 g/mile. For LDV, N₂O measurement should be done from sample storage bags over the light-duty FTP drive cycles. N₂O emission standard of 0.10 g/bhp-hr for heavy-duty engines (HDE) is also finalized. The final N₂O standard becomes effective in 2014 model year for diesel engines. Usually raw or diluted exhaust is measured for HDE emission testing. Therefore, an analyzer capable of measuring N₂O from bag and from diluted sample continuously is required to support both LDV and HDE regulations.