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This paper deals with the effect of combustion chamber shape and the role of pressurized injection in high-speed direct-injection diesel engines. First, the previously reported good performance and emission characteristics of the reentrant chamber were confirmed in a single-cylinder engine test. To obtain a better insight into this excellence, a high-speed gas-sampling method was applied to determine the local fuel-air equivalence ratios and mass fractions of substances having higher boiling points during combustion. The results showed that even at a retarded injection the reentrant chamber suppressed the outflow of gas into the clearance space from containing a lot of higher-boiling-point substances, like raw fuel and carbonaceous matter, thereby assuring a less heterogeneous state than the ordinary deep-bowl chamber. This is attributed partly to the suppressed outflow of unburnt gas from the cavity and partly to the enhanced mixing near the entrance.

A single cylinder, Cummins NH, direct-injection, diesel engine has been operated in order to evaluate the effects of aromatic content and aromatic structure on diesel engine particulates. Results from three fuels are shown. The first fuel, a low sulfur Chevron diesel fuel was used as a base fuel for comparison. The other fuels consisted of the base fuel and 10% by volume of 1-2-3-4 tetrahydronaphthalene (tetralin) a single-ring aromatic and naphthalene, a double-ring aromatic. The fuels were chosen to vary aromatic content and structure while minimizing differences in boiling points and cetane number. Measurements included exhaust particulates using a mini-dilution tunnel, exhaust emissions including THC, CO2, NO/NOx, O2, injection timing, two-color radiation, soluble organic fraction, and cylinder pressure. Particulate measurements were found to be sensitive to temperature and flow conditions in the mini-dilution tunnel and exhaust system.