Combustion and Emission Characteristics of a Small-Bore HSDI Diesel Engine in the Conventional and LTC Combustion Regimes

An experimental investigation was conducted on a small-bore, high-speed diesel engine to study the effect of different operating parameters on combustion and engine-out emissions in the conventional and low temperature regimes. For the conventional diesel combustion, the spray behavior is analyzed and a differentiation is made between the conditions in the small-bore and the larger bore quiescent chamber engines. The effects of the injection pressure, exhaust gas recirculation (EGR), injection timing and swirl ratio (SR) on combustion and engine-out emission are investigated. The trade-off between NOx and smoke, measured in Bosch smoke unit, (BSU), is investigated with a special attention to the low temperature combustion regime, (LTC). The results showed that the LTC regime could be reached at fairly high EGR rates under all the injection pressures investigated in this work. The margin for the variation in EGR was limited just before the misfiring EGR. A small increase in EGR to the firing limit resulted in a drop in both the NOx and BSU, with a noticeable penalty in fuel economy, and an increase in HC and CO emissions. The increase in swirl ratio was effective in reducing both NOx and BSU in the LTC regime, but with some penalty in fuel economy.