Deming Jiang

Engine performance and emissions of a compression ignition engine operating on the diesel-methanol blends

A stabilized diesel-methanol blend was realized and a study on the performance and emissions of the diesel-methanol blend was carried out in a compression ignition engine. The study showed that the engine thermal efficiency increases and the diesel equivalent b.s.f.c. decreases with increase in the oxygen mass fraction (or methanol mass fraction) of the diesel-methanol blends due to an increased fraction of premixed combustion phase, oxygen enrichment and improvement in the diffusive combustion phase. Further increase in the fuel delivery advance angle will achieve a better engine thermal efficiency when the diesel engine is operated using the diesel-methanol fuel blends. A marked reduction in the exhaust CO and smoke can be achieved when operating with the diesel-methanol blend. There is not a large variation in the exhaust hydrocarbon with the addition of methanol in diesel fuel. NOx increases with increase in the mass of methanol added; methanol addition to diesel fuel was found to have a strong influence on the NOx concentration at high engine loads rather than at low engine loads, and a flat NOx-smoke trade-offcurve exists when operating with the diesel-methanol fuel blends.

Combustion characteristics and heat release analysis of a direct injection compression ignition engine fuelled with diesel—dimethyl carbonate blends

Abstract The combustion characteristics and heat release of a direct injection (DI) compression ignition engine fuelled with diesel-dimethyl carbonate blends were investigated on a compression ignition engine. The study showed that the premixed combustion is prolonged and the duration of the diffusive combustion is shortened with increase in the dimethyl carbonate (DMC) addition. For a specific brake mean effective pressure (b.m.e.p.), the maximum cylinder gas pressure, the maximum rate of pressure rise and the maximum rate of heat release increase with increase in the DMC addition at medium and high loads, while they exhibit less variation with the DMC addition at small load. Meanwhile, the maximum gas temperature decreases with increase in the DMC addition. The ignition delay increases while the rapid combustion duration and the total combustion duration show less variation with the DMC addition. The brake specific fuel consumption (b.s.f.c.) increases while the diesel equivalent b.s.f.c. decreases and the thermal efficiency increases with increase in the DMC addition. The CO and smoke decrease with increase in the DMC addition, and NOx does not increase with increase in DMC.

Study of combustion characteristics of a compression ignition engine fuelled with dimethyl ether

Abstract This paper presents the combustion characteristics of a light-duty direct-injection diesel engine operating on dimethyl ether (DME). The indicated pressure diagrams and injector needle lifts are recorded and the combustion characteristics are demonstrated and compared with those of an engine operated on diesel fuel. The experimental and calculated results show that the DME engine has a longer delay of injection and duration of injection, a lower maximum cylinder pressure and rate of pressure rise, as well as a shorter ignition delay compared with those of a diesel engine. The DME engine has a low mechanical load and combustion noise, a fast rate of diffusion combustion and a shorter combustion duration than that of a diesel engine. It has the ideal pattern of compression ignition engine heat release.

Combustion characteristics and heat release analysis of a compression ignition engine operating on a diesel/methanol blend

Abstract A stabilized diesel/methanol blend was developed and the combustion characteristics and heat release analysis of this blend was carried out in a compression ignition engine. The study showed that the increase in the methanol mass fraction will result in an increase in the heat release rate in the premixed burning phase and shorten the combustion duration of the diffusive burning phase. Ignition delay increases with the increase in the methanol mass fraction and the behaviour is more obvious at low engine load and high engine speed. The rapid-burn duration varies little with the methanol mass fraction and the total combustion duration decreases with the increase in the methanol mass fraction. At a low engine speed, the centre of heat release curve tends to be close to the top dead centre (TDC), with an increase in the methanol mass fraction at all engine loads and fuel delivery advance angles, the maximum rate of pressure rise and the maximum rate of heat release increase with the increase in the methanol mass fraction. At a high engine speed, the centre of the heat release curve closes to TDC at high engine load and will depart from TDC at low engine load. The maximum rate of pressure rise and heat release gives an increasing trend with the increase of methanol mass fraction at high engine loads. The maximum cylinder pressure increases with the increase of the methanol mass fraction. The presence of oxygen reduces the peak pressure, but the reduction was found to be insensitive to the proportion of oxygen within the 6–11 per cent range of testing.

Effects of the addition of ethanol and cetane number improver on the combustion and emission characteristics of a compression ignition engine

Abstract Combustion and emission characteristics of a direct-injection diesel engine fuelled with diesel—ethanol blends were investigated. The results show that the ignition delay and the premixed combustion duration increase, while the diffusive combustion duration and the total combustion duration decrease with increase in the oxygen mass fraction in the blends. The addition of 0.2 per cent volume fraction of cetane number improver (isoamyl nitrite) could mean that the ignition delay and the premixed combustion duration of the fuel blends with 10vol% ethanol fraction recover to those of diesel fuel. Meanwhile, with the increase in the ethanol fraction in the fuel blends, the centre of the heat release curve moves closer to the top dead centre. The brake specific fuel consumption increases, while the diesel equivalent brake specific fuel consumption decreases with increase in the ethanol fraction. The exhaust smoke concentration increases and exhaust nitrogen oxide (NO x ) concentration decreases on prolonging the fuel delivery advance angle for both diesel fuel and the blended fuels. For a specific fuel injection advance angle, the exhaust smoke concentration shows a large decrease and the exhaust NO x concentration a small decrease on ethanol addition.

Study on the performance and emissions of a compression ignition engine fuelled with dimethyl ether

Abstract The paper presents the research results of a light-duty direct injection diesel engine operating on dimethyl ether (DME). The effects of the main parameters of the combustion system, such as plunger diameter, nozzle type, fuel delivery advance angle, protruding distance of the nozzle tip from the bottom plane of the cylinder head and swirl ratio, on the performance of the DME engine are investigated. The indicator diagrams are taken after optimizing the combustion system and characteristics of combustion and emissions are measured for DME and diesel operation. The results show that, by adding a pressure pump in the fuel supply system, the vapour lock of DME in the fuel system is eliminated. The engine runs smoothly on DME over a wide range of speeds and loads. The effective thermal efficiency of the DME engine is 3 per cent higher than that of the diesel engine, and a low rate of pressure rise, low combustion noise, smokeless combustion and low NO x emissions of the DME engine can be achieved. The results demonstrate good characteristics in reducing emissions for a diesel engine operating on DME.

Engine performance and emission characteristics of a compression ignition engine fuelled with diesel/dimethoxymethane blends

The performance and emissions of a compression ignition engine fuelled with diesel/dimethoxymethane (DMM) blends were studied. The results showed that the engines thermal efficiency increased and the diesel equivalent brake specific fuel consumption (b.s.f.c.) decreased as the oxygen mass fraction (or DMM mass fraction) of the diesel/DMM blends increased. This change in the diesel/DMM blends was caused by an increased fraction of the premixed combustion phase, an oxygen enrichment, and an improvement in the diffusive combustion phase. A remarkable reduction in the exhaust CO and smoke can be achieved when operating on the diesel/DMM blend. Flat NO x /smoke and thermal efficiency/smoke curves are presented when operating on the diesel/DMM fuel blends, and a simultaneous reduction in both NO x and smoke can be realized at large DMM addition. Thermal efficiency and NO x give the highest value at 2 per cent oxygen mass fraction (or 5 per cent DMM volume fraction) for the combustion of diesel/DMM blends.

Study on cycle-by-cycle variations of combustion in a natural-gas direct-injection engine

Abstract In this paper, the cycle-by-cycle variations of a compressed-natural-gas (CNG) direct-injection (DI) engine were investigated. The results show that the CNG DI engine has a better lean burn capability, and misfire cycles and partial burn cycles exist when the engine operates at small equivalence ratio (>0.4). Meanwhile, the indicated mean effective pressure (IMEP) has a low value, and the high value of the coefficient of variation in the IMEP is presented in comparison with those operating at a high equivalence ratio. Cycles with a high maximum cylinder pressure correspond to the cycles of fast burning, and parameter interdependence is observed between the maximum cylinder gas pressure and its corresponding crank angle, between the maximum rate of pressure rise and its corresponding crank angle, and between the maximum cylinder pressure and the indicated mean effective pressure. Better parameter interdependence exists between the maximum cylinder pressure and the flame- developing period, between the maximum cylinder pressure and the rapid-burning period, and between the accumulated heat release amount per cycle and the indicated mean effective pressure. A small variation in the flame-developing duration will lead to a large variation in the rapid-burning duration under lean mixture combustion; the slow flame propagation speed of the lean mixture combustion is considered to lead to this phenomenon.

Experimental and numerical study of high-pressure-swirl injector sprays in a direct injection gasoline engine

Abstract The characteristics of free spray of a new type high-pressure-swirl injector in gasoline direct injection (GDI) engine under various injection conditions are investigated. The fuel spray with hollow-cone structure, wide spreading, and large spray angle is observed under the injection condition simulating to the GDI engine operation at full load. The study shows that a vortex structure can be clearly observed in the periphery of the spray. Meanwhile, an initial spray slug also appears at the tip of the main spray. Under the injection condition of GDI engine partial load, the structure of fuel spray changes into the more compact and solid-cone shape with decreased spray width. Moreover, the influences of the injection pressures and ambient pressures on the spray characteristics of the injector are studied. Along with the experimental studies, a general numerical model for the swirl spray is developed. Then, the model is implemented into a multi-dimensional computational fluid dynamics code (KIVA-3V) to theoretically study the pressure-swirl injector sprays. Comparisons between the computed and measured spray characteristics such as spray structure, spray tip penetration, and droplet sizes are made, and good agreement has been achieved between the model prediction and measurement.

An Investigation on Simulation Models and Reduction Methods of Unburned Hydrocarbon Emissions in Spark Ignition Engines

In this paper, the formation mechanisms of unburned hydrocarbons in the cylinder of spark ignition engine are investigated and the prediction model of unburned hydrocarbon formation and desorption in top land crevice, in the layers of lubricating oil on the cylinder liner and in deposits on the combustion chamber in spark ignition engines are established. The effects of different top land crevice widths, engine speeds, air fuel ratios and spark advance angles on engine exhaust unburned hydrocarbons are investigated. It is shown that the optimum width of engine top land crevice is 0.32 mm (1.3 times of the two wall quenching distance), thus the flame can get into the bottom of crevice and burns out all of the accumulated unburned hydrocarbons in it, consequently the engine exhaust hydrocarbons can be greatly reduce by 35∼50% and with less penalty on engine power output and fuel economy 0.5 ∼ 1.5% loss in power output and 1 ∼ 3% loss in fuel economy), the predicting values by the models match well with the ...