Libin Ji

Experimental study on dual-fuel compound homogeneous charge compression ignition combustion:

This paper investigates the combustion and emission characteristics of dual-fuel compound homogeneous charge compression ignition combustion. n-heptane and oxygen-containing alcohols were chosen as the port-injection fuel and the in-cylinder direct-injection fuel, respectively. It is found that compound homogeneous charge compression ignition combustion with n-heptane port injection and alcohol direct injection exhibits a three-stage combustion process containing n-heptane low-temperature reactions, high-temperature reactions and alcohol combustion. The crank angle position at which 10% of the mass fraction is burned is mainly dominated by the fuel heat value per cycle of premixed fuel, and is advanced with increasing the fuel heat value per cycle of premixed fuel and premixed ratio. The crank angle position at which 50% of the mass fraction is burned shows remarkable sensitivity to the premixed ratio, and is advanced considerably as the premixed ratio and the fuel heat value per cycle of premixed fuel increase. Burn duration increases with increasing total fuel heat value per cycle and fuel heat value per cycle of directly injected fuel. The results show that compound homogeneous charge compression ignition combustion could successfully reach the full load of the prototype engine. The indicated thermal efficiency is very close to the prototype engine. However, their CO and hydrocarbon emissions are relatively higher. It is worth noting that compound homogeneous charge compression ignition combustion with alcohol direct injection can reduce nitrogen oxide and soot emissions simultaneously. Nitrogen oxide emissions can be reduced below 100 ppm, and smoke opacity is below 15% at the full-load ranges. Moreover, with increasing oxygen content of directly injected fuels, soot emission of compound homogeneous charge compression ignition combustion decreases. Ethanol direct injection could make compound homogeneous charge compression ignition combustion nearly smoke free at the full-load ranges.

Influence of Fuel Supply Timing and Mixture Preparation on the Characteristics of Stratified Charge Compression Ignition Combustion with N-Heptane Fuel

Stratified charge compression ignition (SCCI) combustion was investigated on a single-cylinder, four-stroke diesel engine with n-heptane. A premixed atmosphere was realized by the early injection at the intake port, while the rest of fuel was directly injected into the cylinder. Premixed ratio (defined as the ratio of fuel amount in port injection divided by the total fuel amount in the charge) and fuel supply timing of direct injection were altered to explore their influences on SCCI combustion, emission, and engine performance characteristics. The results show that increased premixed ratio and earlier fuel supply timing can remarkably enhance the peak cylinder temperature and pressure while shortening the main combustion duration. NOx is strongly dependent on fuel supply timing, whereas premixed ratio and equivalence ratio play a secondary role. CO can be effectively reduced by increasing premixed ratio and advancing fuel supply timing. HC rises with increasing premixed ratio but is insensitive to the change of fuel supply timing. Finally, indicated thermal efficiency (ITE) drops with retarded fuel supply timing, and the maximum indicated mean effective pressure (IMEP) can be achieved by optimizing the premixed ratio and fuel supply timing.

Experimental study on partially premixed compression ignition combustion fueled with a low octane number primary reference fuel using two-stage fuel supplying

An experimental study of partially premixed compression ignition combustion with low octane fuel was conducted on a single-cylinder engine. The effects of the external exhaust gas recirculation and intake boost on this partially premixed compression ignition combustion and emissions were investigated. During the experiments, a trade-off relationship between the NOx and smoke emissions was observed in this partially premixed compression ignition combustion. However, heavy exhaust gas recirculation usage has the potential to decrease NOx and soot emissions simultaneously at the expense of the fuel economy. It is determined that at an increased intake port pressure, the maximum in-cylinder pressure increases, and the ignition timing of the high-temperature combustion is retarded. Also, the peak value of the low-temperature combustion is slightly depressed, the peak value of the high-temperature heat release decreases significantly, and the maximum value of the diffusing burn increases to some extent. Compared to natural aspirated condition, the partially premixed compression ignition combustion with intake boost has the capability of simultaneously reducing NOx and soot emissions to ultra-low levels, that is, the intake boost could be an important strategy for the combustion and emission improvement in this advanced engine combustion mode.