Xinqi Qiao

New controllable premixed combustion for dimethyl ether engine

A new concept of the controllable premixed combustion (CPC) system was proposed for dimethyl ether (DME) to explore a new approach to achieving ultra-low NOX emissions with the zero level of particulate matter exhaust emissions. The DME fuel was injected into the premix chamber by means of the electronically controlled low pressure injection system, then the mixture formation and combustion process were controlled with a control-valve set between the main chamber and the premix chamber. The test bench was constructed based on a single diesel engine. Preliminary studies demonstrated that ultra-low NOX emissions had been realized with zero particulate matter emissions under the optimum specifications of the DME engine, NOX emissions were less than 65 × 10−6. According to the engine combustion analysis, it was found that the control-valve played an important role in the pre-mixture formation and ignition timing.

Combustion and soot emission characteristics of soybean biodiesel in constant volume chamber

ABSTRACT An optically accessible constant volume chamber was adopted to investigate the combustion and soot emission characteristics of soybean biodiesel under 800, 900, 1000, and 1200 K initial ambient temperatures. Results showed that with the decrease of initial ambient temperature ignition delay prolonged and heat release rate transited from mixing controlled combustion to premixed dominate combustion mode. As the initial temperature decreased, natural flame luminosity gradually decayed, which indicated lower soot emission at lower initial ambient temperature.

Flexible fuel engine based on multi-combustion control technologies

A combustion control strategy is proposed for diesel engine to reduce PM and NOx emissions significantly, which adopts some technologies including internal exhaust gas recirculation (EGR), split spray, adjustable fuel delivery advance angle and the application of alternative fuels. Based on this strategy, a flexible fuel engine has been developed. The experimental results show that this engine can be fueled with diesel fuel, alcohol, dimethyl carbonate (DMC), etc. It works with extremely low levels of particulate matter (PM) and NOx, 2–3% higher effective thermal efficiency on moderate and high loads when alternative fuels are used. This engine not only has lower exhaust emissions, but also can be fueled with those alternative fuels, which are difficult to be ignited by compression.

Effect of the addition of ethanol on the combustion and emission characteristics of a common-rail dimethyl ether engine

The effect of the addition of ethanol on the combustion and emission characteristics of dimethyl ether combustion were investigated in this study using an electronically controlled common-rail dimethyl ether engine. The ignition delay, the crank angle for 50% mass fraction burned, the combustion duration, the nitrogen oxide emissions, the hydrocarbon emissions and the carbon monoxide emissions of the fuel blends with the addition of different percentages of ethanol were analysed for different loads and for different injection timings separately. The results suggest that the effect of ethanol on the dimethyl ether combustion mainly prolongs the ignition delay and inhibits the combustion rate. The ignition delay is prolonged significantly with increasing percentage of ethanol added for low loads or retarded injection timings. A reduction in the combustion rate and an increase in the combustion duration are associated with a higher percentage of ethanol added for high loads or advanced injection timings, leading to lower nitrogen oxide emissions. On the addition of 15% ethanol, the nitrogen oxide emissions are reduced by about 17% for a brake mean effective pressure of 1.2 MPa, and by 32% when the start of injection is at −7° crank angle after top dead centre. Premixed combustion with a sharply prolonged ignition delay and a shortened combustion duration can be achieved by the addition of 15% ethanol when the start of injection is at 5° crank angle after top dead centre. The carbon monoxide emissions show a tendency to increase with increasing amount of ethanol added, whereas the hydrocarbon emissions remain nearly the same until the percentage of ethanol reaches 15%.

An experimental and computational investigation of the effects of temperature on soot formation mechanisms

Effects of the initial ambient temperature on combustion and soot emission characteristics of diesel fuel were investigated through experiments conducted in an optical constant volume chamber and simulation using a phenomenological soot model. Four different initial ambient temperatures were adopted in this research: 1000, 900, 800 and 700 K. In order to obtain a better prediction of soot behavior, the phenomenological soot model was revised to take into account the feedback of soot oxidation on the soot number density and good agreement was observed in the comparison of soot measurement and prediction. The results indicated that the ignition delay was prolonged with decreasing initial ambient temperature. The heat release rate demonstrated the transition from mixing controlled combustion at high ambient temperatures to the premixed combustion mode at low ambient temperatures. At lower ambient temperatures, soot formation and the oxidation mechanism were both suppres- sed. However, the soot mass concentration was finally reduced with decreasing initial ambient temperature. Although the drop in ambient temperature did not cool the mean in-cylinder temperature during the combustion, it did shrink the total area of local high equivalence ratios, in which soot usually is rapidly generated. At an initial ambient temperature of 700 K, soot emissions were almost negligible, which indicates that sootless combustion might be achieved under super low initial temperature operation conditions.