Study On Performance And Emission Of High Speed Diesel Engine Fuelled With N-Butanol Diesel Blends Under Low Temperature Combustion

Low temperature combustion in diesel engine utilize a large amount of exhaust gas recirculation (EGR) generally to reduce the in-cylinder combustion temperature, thus decreasing the emission of NOx and soot simultaneously and solving the problem of the tradeoff between NOx and soot emission. However, applying a large EGR caused decreasing the combustion quality, reducing the combustion efficiency and increasing the emission of HC.Add n-butanol into diesel can decrease the cetane number of blends and get a longer ignition delay to provide enough time for mixing between fuel and air, reducing the in-cylinder combustion temperature dramatically. Therefore, experimental and simulative method were used to study effect of different parameters on the combustion characteristic of high speed engine in low temperature combustion which realize by adding large amount of n-butanol at medium EGR.Firstly, experiments were performed to study effect of injection strategies (included injection timing, injection pressure and pilot injection) on the combustion characteristic of high speed engine under low temperature combustion. Results indicated that, with the main injection time advancing, the maximum pressure rise rate, peak pressure of in-cylinder, peak value of heat release rate increased, the NOx emission increased and the soot emission increases first and then decreases; with the injection pressure increasing, the peak pressure of in-cylinder and the peak value of heat release rate increased, the CA50advanced, the NOx emission increased, while the soot is opposite; with the pilot injection timing advancing, the peak pressure of in-cylinder decreased, while the maximum pressure rise rate increased, the peak value of pilot injection fuel heat release rate decreased and the peak value of main injection fuel heat release rate increased, the emission of NOx and soot decreased; with the pilot injection fuel mass increasing, the peak pressure of in-cylinder decreased, the peak value of pilot injection fuel heat release rate increased and the peak value of main injection fuel heat release rate decreased, the CA50advanced, the emission of NOx increased and soot emission decreases first and then increases; moreover, with the n-butanal ratio increasing, the maximum pressure rise rate increased, CA50advanced, the emission of soot NOx decreased and the effect of injection timing on NOx emission become weak; with the EGR increasing, the maximum pressure rise rate decreased, the soot emission increased, NOx emission decreased and the effect of injection pressure on NOx emission become weak.Secondly, the combustion model of engine was built by using AVL-FIRE software coupled with CHEMKIN, and the n-heptane-n-butanol-PAH-toluene reduced mechanism was used as n-butanol-diesel blend fuel combustion chemical reaction kinetics mechanism to study effect of n-butanol proportion, EGR rate, injection timing and pilot injection timing on the formation of NO, NO2and soot precursors benzene(Ai), naphthalene(A2), phenanthrene(A3), pyrene(A4) of n-butanol-diesel blended fuel in low temperature combustion. Results indicated that, with the n-butanal proportion increasing, the formation timing of NO, NO2and PAHs delayed. The final formation of NO and PAHs decreased, while NO2increases first and then decreases. With the EGR rate increasing, the formation timing of NO, NO2and PAHs delayed. The final formation of NO and NO2decreased, while PAHs show different trend at different n-butanol proportion. With the main injection time advancing, the formation timing of NO, NO2and PAHs advanced. The final formation of NO increased, while NO2, A1and A2decreased, A3and A4increases first and then decreases. With the pilot injection timing advancing,The final formation of NO decreased, NO2increased, A1and A2decreases first and then increases, A3increases first and then decreases, A4decreased.