Search Results

Low temperature combustion (LTC) may allow simultaneous reduction of nitrogen oxides (NOx) and soot with acceptable compromise in the efficiency of a diesel engine. Recently oxygenate biodiesel fuels were tested to resolve the problem of CO emission at higher exhaust gas recirculation (EGR) rates in LTC operation. In this paper 3-D simulation is performed by KIVA with soybean biodiesel blends of D100 and BD20 for a heavy duty test engine. The oxygen fraction in intake gas is controlled between 7% and 19% to simulate EGR in LTC operation. A surrogate mechanism is constructed by combining the skeletal mechanisms of methyl butanoate (MB) and n-heptane for low and high temperature chemistry. It consists of 76 species and 243 reaction steps with detailed NOx chemistry. The conditional moment closure (CMC) model is employed to address coupling between turbulence and chemistry.

A nano-sized PM and THC emission characteristics were investigated according to the fuel injection strategy such as a pressure and timing in the GDI engine. On the part-load condition, the particulate emissions exhibited a strong sensitivity to the injection timing. The fuel injection pressure also had a great association with the nano-particles and THC. A size of PM exhausted from the GDI engine located near 10nm on the part-load. In contrast, accumulation mode particles within 60 - 80nm mainly exhausted during the cold transient start phase. Increment of fuel injection pressure positively affected on the nano-particle and THC emissions during the start of the engine, as well.

The characteristics of diesel spray injected into the cylinder provide crucial clues to the perception of the combustion performance in a compression ignition engine. In this study, five different diesel common rail injectors were examined which have different hole numbers, orifice sizes, jet cone angles, and hydraulic flow rates. Both the macroscopic and microscopic characteristics of diesel sprays were compared through Mie-scattered light imaging and PDA (Phase-Doppler anemometry) measurements. Seven hole injector with smaller hole was found to give better air/fuel mixing and favorable droplet size compared with other injectors. To evaluate the feasibility of achieving lower emission level with the different diesel sprays, the combustion and emission characteristics in case of 6 and 7 hole injectors were investigated under the same fuel flow rate condition in a light duty DI diesel engine.

Dimethyl Ether (DME) seems to be one of the most attractive alternative fuels for heavy-duty engines. Many researches[5, 6, 7, 8, 9 and 10] and developments have been carried out on DME engines. However, the principal technical problems have not yet been solved enough. One problem is related to finding safety fuel supply systems able to suppress vaporizations. To search for these systems, we have studied optimization of injection equipment in terms of the relation between performances and emission characteristics by using Common Rail injection systems. We have found that thermal efficiency and emissions is satisfactory when the engine is operated at 50MPa, 14 degree BTDC. Also, when the pilot injection by common rail is 10%, NOx emission reduced up to 30%. And the brake thermal efficiency is optimum when the nozzle needle lift is 0.21mm for test engines.