Liu Shenghua

Combustion characteristics of compressed natural gas/diesel dual-fuel turbocharged compressed ignition engine

Abstract The combustion characteristics of a turbocharged natural gas and diesel dual-fuelled compression ignition (CI) engine are investigated. With the measured cylinder pressures of the engine operated on pure diesel and dual fuel, the ignition delay, effects of pilot diesel and engine load on combustion characteristics are analysed. Emissions of HC, CO, NOx and smoke are measured and studied too. The results show that the quantity of pilot diesel has important effects on the performance and emissions of a dual-fuel engine at low-load operating conditions. Ignition delay varies with the concentration of natural gas. Smoke is much lower for the developed dual-fuel engine under all the operating conditions.

Study on the Performance and Emissions of a Compression Ignition Engine Fuelled with Fischer-Tropsch Diesel Fuel

Abstract Fischer-Tropsch (F-T) diesel fuel is characterized by a high cetane number, a near-zero sulphur content, and a very low aromatic level. In the present paper, the performance and emissions of an unmodified single-cylinder direct injection diesel engine operating on F-T diesel fuel are studied and compared with those of conventional diesel fuel operation. The results show that F-T diesel fuel exhibits a slightly longer injection delay and injection duration, displays an 18.7 per cent average shorter ignition delay, and has a lower peak value of premixed burning rate and a higher peak value of diffusion burning rate than conventional diesel fuel. The engine with F-T diesel fuel has a slightly lower peak combustion pressure and a far lower rate of pressure rise, and consequently a lower mechanical load and combustion noise compared with conventional diesel fuel. In addition, the brake specific fuel consumption is lower and the brake fuel conversion efficiency is higher for F-T diesel fuel operation. The CO2, HC, CO, NO x , and smoke emissions with F-T diesel fuel are reduced at all operating conditions when compared with conventional diesel fuel. On average, NO x and smoke emissions are reduced by 16.7 and 40.3 per cent respectively with F-T diesel fuel. The study demonstrates that F-T diesel fuel is an excellent clean alternative fuel for diesel engines.

Decreasing hydrocarbon and carbon monoxide emissions of a natural-gas engine operating in the quasi-homogeneous charge compression ignition mode at low loads

Abstract Experimental studies have been carried out on decreasing the hydrocarbon (HC) and carbon monoxide (CO) emissions of a compressed natural-gas (CNG) engine operating in quasi-homogeneous charge compression ignition (QHCCI) mode at low loads. The effects of three technical approaches including partial gas cut-off (PGC), intake air throttling, and increasing the pilot fuel quantity on emissions and the brake thermal efficiency of the CNG engine are studied. The results show that HC and CO emissions can be reduced with only a small penalty on the brake thermal efficiency. An increase in the brake thermal efficiency and reductions in HC and CO emissions can be simultaneously realized by increasing the pilot fuel quantity. It is also indicated from experiments that the HC and CO emissions of the engine can be effectively reduced when using intake air throttling and increasing the pilot fuel quantity are both adopted. However, nitrogen oxide (NOx) emissions increase with increase in the throttling and the pilot fuel quantity. Under PGC conditions, NOx emissions are lower than those in the standard mode; however, they increase and exceed the values in the standard mode in increases in the load and natural-gas supply.

Experimental studies on the combustion characteristics and performance of a naturally aspirated, direct injection engine fuelled with a liquid petroleum gas/diesel blend

Abstract This paper studies the combustion characteristics and performances of a LPG/diesel blend-fuel engine; the influences of mixing ratio of LPG in diesel on the ignition timing, in-cylinder pressure, heat-release rate, specific fuel consumption, power output, and exhaust emissions have been identified. The results indicate that the ignition delay of blend fuel was obviously longer than that of diesel and the higher the mixing ratio of LPG in diesel, the longer the ignition delay. When the mixing ratio of LPG in diesel was 10 per cent, the peak in-cylinder gas pressure and the peak rate of pressure rise were slightly higher than those of diesel, and the corresponding crank angles at which the peak values occurred were almost the same as those of diesel. When the mixing ratio was 30 per cent, the peak in-cylinder pressure and the peak rate of pressure rise were lower than those of diesel, and the corresponding crank angles were retarded. With the increasing of mixing ratio of LPG in diesel, the peak rate of heat release increased and the corresponding crank angles were retarded. The equivalent specific fuel consumption of L10 was the same as that of diesel, but that of L30 was slight higher. The power output of the diesel engine was higher than those of L10 and L30 at speed characteristic of full load, especially at high engine speed. With the increasing of mixing ratio, the smoke emissions and NOx emissions were greatly reduced, and CO emissions decreased too, but HC emissions slightly increased.

Combustion and emission characteristics of a homogeneous charge compression ignition engine

Abstract Dimethyl ether (DME) is a kind of fuel with high cetane number and low evaporating temperature, which is suitable for a homogeneous charge compression ignition (HCCI) engine. The combustion and emission characteristics of an HCCI engine fuelled with DME were investigated on a modified single-cylinder engine. The experimental results indicate that the HCCI engine combustion is a two-stage heat release process. The engine load or air-fuel ratio has significant effects on the maximum cylinder pressure and its position, the shape of the pressure rise rate and the heat release rate. The engine speed has little effect. A DME HCCI engine is smoke free, with zero NOx and low hydrocarbon and CO emissions under the operating conditions of 0.25–0.30 MPa brake mean effective pressure.

Effects of compression ratio on the combustion characteristics of a homogeneous charge compression ignition engine

The effects of homogeneous charge compression ignition (HCCI) engine compression ratio on its combustion characteristics were studied experimentally on a modified TY1100 single cylinder engine fueled with dimethyl ether. The results show that dimethyl ether (DME) HCCI engine can work stably and can realize zero nitrogen oxides (NOx) emission and smokeless combustion under the compression ratio of both 10.7 and 14. The combustion process has obvious two stage combustion characteristics at ɛ = 10.7 (ɛ refers to compression ratio), and the combustion beginning point is decided by the compression temperature, which varies very little with the engine load; the combustion beginning point is closely related to the engine load (concentration of mixture) with the increase in the compression temperature, and it moves forward versus crank angle with the increase in the engine load at ɛ = 14; the combustion durations are shortened with the increase in the engine load under both compression ratios.

The Effects of Methanol Fraction on the Azeotropic Behaviors of Methanol/Gasoline Mixtures

Methanol is regarded as a potential alternative fuel for spark ignition (SI) engine. It is feasible for SI engines to run on methanol/gasoline mixtures. When methanol is mixed with gasoline, the physicochemical properties of the mixtures are changed different from the properties of both methanol and pure gasoline to some extent. This paper focused on the azeotropic behaviors of saturated vapor pressure (ps) and the distillation curves of methanol/gasoline mixtures. And compositions of the distillates were identified and quantified by a gas chromatography—mass spectrometry (GC–MS) under various Td. Experimental results show that the ps and distillation curves of methanol/gasoline mixtures showed strong positive deviation of Raoult’s law. The maximum deviation occurred around the Td of methanol’s boiling point, i.e., 64.5°C. Increasing the heavy hydrocarbon contents in gasoline could draw the Td of methanol/gasoline mixtures back to that of base gasoline. C4–C8 alkanes, olefins, and benzenes were the main components in distillates of gasoline and its methanol mixture. However, the additive with hetero atom of oxygen, methyl tertiary butyl ether (MTBE) was the leading component with the largest mass percentage in all the distillates, while methanol was another leading component in methanol mixture distillates. Methanol co-boiled with all of the gasoline components rather than with some certain ones; even so, pentane, 2-methyl-2-butene and toluene were the three leading azeotropes with the change ratio of over 4% in mass percentage.