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This paper is concerned with the effects of temperature of heavy fuels on combustion and engine performance in a naturally aspirated DI diesel engine. Engine performance and exhaust gas emissions were measured for rapeseed oil, B-heavy oil, and diesel fuel at fuel temperatures from 40°C to 400°C. With increased fuel temperature, mainly from improved efficiency of combustion there were significant reductions in the specific energy consumption and smoke emissions. It was found that the improvements were mainly a function of the fuel viscosity, and it was independent of the kind of fuel. The optimum temperature of the fuels with regard to specific energy consumption and smoke emission is about 90°C for diesel fuel, 240°C for B-heavy oil, and 300°C for rapeseed oil. At these temperatures, the viscosities of the fuels show nearly identical value, 0.9 - 3 cst. The optimum viscosity tends to increase slightly with increases in the swirl ratio in the combustion chamber.

Two laboratory engines, one direct, injection and one indirect injection, were operated for a range of speeds, loads, injection timings, fuels, and steady and transient conditions. Rate of combustion data were derived and analyzed using a double Wiebe's function approximation. It is shown that three of the six function parameters are constant for a wide range of conditions and that the other three can be expressed as linear functions of the amount of fuel injected during ignition lag. Engine noise, smoke, and thermal efficiency correlate with the parameters describing the amount of premixed combustion and diffusive combustion duration. These characteristics may be optimized by reducing the quantity of premixed combustion while maintaining the duration of diffusive combustion to less than 60°CA.

This paper deals with the effects of flash-boiling injection of various kinds of fuels on spray characteristics, combustion, and engine performance in DI and IDI diesel engines. It is known that spray characteristics change dramatically at the boiling point of fuel. When the fuel temperature increases above the boiling point, the droplet size decreases apparently and the spray spreads much wider. At higher fuel temperatures, above the boiling point, the apparent effects are a lower smoke density and improved thermal efficiency at higher loads, resulting from the shorter combustion duration; it is thus possible to obtain a markedly improved engine performance in engines with a low air-utilization chamber. Remarkable changes in heat release with the increase in fuel temperature are; an increase in premised combustion quantity and shortening of the combustion duration. The changes in smoke emission and thermal efficiency for different engine types are also considered in this paper.

The purpose of this investigation is to evaluate the feasibility of rapeseed oil and palm oil for diesel fuel substitution in a naturally aspirated D.I. diesel engine, and also to find means to reduce the carbon deposit buildup in vegetable oil combustion. In the experiments, the engine performance, exhaust gas emissions, and carbon deposits were measured for a number of fuels: rapeseed oil, palm oil, methylester of rapeseed oil, and these fuels blended with ethanol or diesel fuel with different fuel temperatures. It was found that both of the vegetable oil fuels generated an acceptable engine performance and exhaust gas emission levels for short term operation, but they caused carbon deposit buildups and sticking of piston rings after extended operation.

Spark-assisted diesel engines operated with alcohol fuels usually display misfiring or knocking problems. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a swirl chamber diesel engine with a multi-spark ignitor. In the experiments, cycle-to-cycle combustion variations and the degree of knocking were investigated by changing engine parameters over a wide operating range. The results of the investigations showed that stable ignition and smooth combustion is achieved when a flammable mixture is formed in the vicinity of the spark plug when only a small amount of the injected fuel has evaporated. By optimizing the design factors, operation with high efficiency and low exhaust emissions was achieved.

Many of the promissing alternative fuels have relatively low cetane numbers, and may-result in combustion variation problems. This paper presents the chracteristics of the cycle-to-cycle combustion variations in diesel engines, and analyzes and evaluates the mechanism. Combustion variations appear in various forms, such as variations in ignition lag, indicated mean effective pressure, maximum combustion pressure, or rate of heat release. These variations are clearly correlated, and it is possible to represent the combustion variations by the standard deviation in the combustion peak pressure. The combustion variations are random (non-periodic), and are affected by ethanol amount, intake air temperature, engine speed and other various operating conditions.

Forced ignition with glow plugs has great potential for the utilization of alcohol fuels in diesel engines. However, the installation of glow plugs may cause misfiring or knocking in parts of the operating range. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a glow plug-assisted diesel engine; these factors may be classified into two categories: the factors related to the temperature history of the drop lets before contact with the glow plug, and those related to the probability of contact. By optimizing these factors, the combustion difficulties were successfully eliminated over the whole operating range, and engine performance comparable with conventional diesel operation was achieved.

This paper reports the results of two parallel investigations: An investigation on the solubility of alcohols in diesel fuels, and the diesel engine performance with the blended fuels. The investigation proposes an empirical formula for the solubility of alcohols in diesel fuels, as a function of temperature, water content, additive concentration and specific gravity of the diesel fuel. The engine performance when using the blended fuels was also investigated. Compared with conventional diesel fuels, the blended fuels show promise of better thermal efficiency, smoke free operation, and reduction of HC, NOx, and CO emissions.

In a four-cycle, naturally aspirated, pre-chamber diesel engine, the combustion characteristics such as the rates of fuel injection, the ignition lag, the rates of heat release, the combustion peak pressure, the maximum rates of pressure rise, and the smoke density, were investigated for over 70 consecutive cycles under acceleration, with the aid of an on-line data handling system developed for this experiment. The effects of operating conditions such as the fuel injection timing, the fuel spray angle, the wall temperature of the combustion chamber, and the coolant temperature, on the combustion characteristics were also investigated.

With the aid of static mixer and non-ionic emulsifying agent, a comparatively stable water-fuel emulsion was obtained. Engine performance in a 4 cycle direct injection engine using these fuels were studied. A large reduction of NOx concentration was obtained over the wide range of engine operation, in spite of increased ignition lag and rapid combustion. Furthermore, improvements of economy and reduction of exhaust smoke were obtained. The reduction of NOx concentration, fuel consumption and smoke were even more remarkable when compared with operating same engine with water fumigation.