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The aim of this work is to investigate the effect of the blending ratio and pilot injection on the spray and combustion characteristics of biodiesel fuel and compare these factors with those of diesel fuel in a direct injection common-rail diesel engine. In order to study the factors influencing the spray and combustion characteristics of biodiesel fuel, experiments involving exhaust emissions and engine performance were conducted at various biodiesel blending ratios and injection conditions for engine operating conditions. The macroscopic and microscopic spray characteristics of biodiesel fuel, such as injection rate, split injection effect, spray tip penetration, droplet diameter, and axial velocity distribution, were compared with the results from conventional diesel fuel. For biodiesel blended fuel, it was revealed that a higher injection pressure is needed to achieve the same injection rate at a higher blending ratio. The spray tip penetration of biodiesel fuel was similar to that of diesel. The atomization characteristics of biodiesel show that it has higher Sauter mean diameter and lower spray velocity than conventional diesel fuel due to high viscosity and surface tension. The peak combustion pressures of diesel and blending fuel increased with advanced injection timing and the combustion pressure of biodiesel fuel is higher than that of diesel fuel. As the pilot injection timing is retarded to 15deg of BTDC that is closed by the top dead center, the dissimilarities of diesel and blending fuels combustion pressure are reduced. It was found that the pilot injection enhanced the deteriorated spray and combustion characteristics of biodiesel fuel caused by different physical properties of the fuel.

An experimental investigation was performed on the combustion performance, reduction characteristics of exhaust emissions, and engine performance of a spark ignition engine fuelled with bioethanol, ethanol-gasoline blend, and gasoline fuel. The test fuels were an ethanol-gasoline blend (E85), which consists of 85 vol % bioethanol and 15 vol % gasoline, pure bioethanol (E100), and gasoline fuel without any additives (G100). In this work, the combustion and exhaust emission characteristics, including the combustion pressure, brake mean effective pressure (BMEP), and maximum brake torque (MBT) timing of the ethanolgasoline blend and pure ethanol, were compared with those obtained with gasoline fuel. For the comparison of combustion and emissions characteristics for bioethanol, ethanol blends, and gasoline, the experiments were carried out under various engine operating conditions and the results were compared with those obtained using conventional gasoline fuel.The results of this study showed that an ethanol-blended fuel or pure ethanol led to a drastic decrease in exhaust emissions under all operating conditions. The exhaust emissions such as hydrocarbons, carbon monoxide, and nitrogen oxides were reduced when using the bioethanolblended and undiluted ethanol fuel because of the highly oxygenated component of ethanol fuel. Because the ignition timing was advanced above MBT timing when the ethanol fuels were used, improved combustion stability and a better combustion phase were measured because of the high octane rating of the ethanol. Combustion performance such as the brake torque and BMEP remained nearly the same or increased over those found using conventional gasoline fuel under various spark ignition timings and throttle valve openings.

The aim of this paper is to investigate the effects of injection parameters and the exhaust gas recirculation (EGR) rate on the morphological characteristics of soot particulates and exhaust emissions in a common-rail direct-injection (DI) diesel engine with a piston displacement of 1.58 L. To investigate the influences of injection parameters and the EGR rate on the particulate morphology and exhaust emission characteristics, several different injection parameters and two EGR rates were investigated. The particulate morphology (including primary particles), the size of the soot agglomerates, the number of agglomerates, and the fractal dimension were also investigated under various injection strategies, pilot injection quantities, and percentage of EGR. The dependence of air pollution components in engine emissions, such as soot, nitrogen oxide (NO x ), carbon monoxide (CO), and hydrocarbon (HC), upon pilot injection parameters and percentage of EGR at constant operating conditions was measured. A thermophoretic sampling method with a scanning electron microscope (SEM) was used to obtain the soot morphology characteristics. The soot quantity gradually increased with the increase of the pilot injection quantity at the EGR test. It is confirmed that the pilot injection quantity and rate of EGR strongly influenced soot morphological parameters. As the pilot injection quantity is increased, the size of the agglomerates and the number of agglomerates were gradually increased. The results of the PM morphological analysis indicate that the average radius of gyration and number of particles in the agglomerate increased with the increase of the EGR rate. These PM morphology parameters strongly influenced the soot mass, which also increased significantly with the increase of the EGR rate.

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