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To improve engine performance parameters such as smoke, NOx, and BSFC in a DI diesel engine, water-in-gas oil emulsified fuel was used without high pressure or high injection rate. It was confirmed that when compared with high pressure and high injection rate operation with gas oil, emulsified fuel gives significant reductions in NOx concentration, improved fuel economy, and reduced smoke density at ordinary injection pressure and retarded timings.

To get accurate indicator diagrams without the use of pressure transducers, the strain and the displacement of the various parts of engine structures that would have some relationship with the pressure variation in the cylinder were measured and analyzed mathematically. By measuring the strain of the cylinder head bolts, the horizontal displacement of the crank shaft end, and the vertical displacement of the intake valve stem, we realized that the indicator diagrams could be obtained easily without a passage from the interior to the outside of the combustion chamber. Accurate indicator diagrams were estimated by applying the pressure-strain diagram obtained from the static pressure test in the cylinder to the strain variation in the cylinder head bolts. On this occasion, the accuracy of the estimated indicator diagrams could be improved by providing the cylinder head system with a one degree freedom vibration system.

Fuel properties are a very important factor to reduce particulate matter (PM) and other emissions with diesel engines. Especially the effect of aromatic contents has been discussed, though details of the influence differ in different reports. In this study the mechanism of PM formation was investigated in a small direct injection diesel engine. The fuels tested were paraffinic hydrocarbons (C7∼C12) with different boiling points (98∼216 °C), and the blending of aromatic hydrocarbons (1∼4 rings) with paraffinic and olefinic hydrocarbons. The effect of the structure of fuels with the same carbon numbers (dodecane and dodecene) was also investigated. The results showed that the amount of SOF decreases to about one tenth of that of diesel oil when using low boiling point paraffinic hydrocarbons like heptane. However, the total amount of unburned hydrocarbon increases due to over-leaning of the mixture due to the early evaporation.

This paper presents a theory and its experimental validation for air entrainment changes into fuel sprays in DI diesel engines. The theory predicts air entrainment changes for a variety of swirl speeds, number of nozzle holes, nozzle diameters, engine speeds, injection speeds and fuel densities. The formulae of the theory are simple non-dimensional equations, which apply for different sized engines. Experiments were performed to compare theoretical predictions and experimental results in six different engines varying from 85 to 800mm bore. All results showed good agreement with the theoretical predictions for shallow-dish piston engines. However the agreement became poor in the case of deep cavity piston engines. With the theory, it is possible to interpret a variety of combustion phenomena in diesel engines, providing additional understanding of diesel combustion processes.

Diesel passenger car is superior to gasoline engine car in the fuel economy, but it has some defects to improve :noise, startability, particulate and transient performance, etc. Among these problems, this paper presents particularly transient performance in a diesel engine and clarifies the causes of its decline at lower temperature operation. As the results, it is found that the transient torque at the early stage of acceleration is only 50% at −20°C, and that when coolant temperature went up to 20°C, the transient torque approaches to that of the warmed up engine. The transient response becomes worse with retarding the injection timing and with decreasing the engine speed. On the other hand, since the normal response is not obtained despite of using high cetane number fuel, main cause of the inferior transient torque is not the poor combustion, but the increase of friction or cooling loss.

EGR reduces NO emission, but increases smoke and decreases BMEP in diesel engines. This paper describes the relationships between these behaviors and the effect of decreased oxygen with EGR in direct injection, pre-chamber, and turbocharged diesel engines. The results indicate that the reduction of NO depends on decreasing the rate of the incoming oxygen. The increase in smoke and the decrease in BMEP is due to a reduced rate of exhaust oxygen. Also the reduction of NO is due to increased ambient humidity which can be explained by the decreased oxygen in the incoming charge. With these results, it becomes possible to predict the ratio of the reduction of NO emission, the increase in smoke and the decrease in BMEP.

To clarify the microcrystal structure of soot particulate in the combustion chamber, we examined sampling methods which freeze the reaction of sample specimens from the combustion chamber and collected the soot particulates on microgrids. We investigated the microcrystal structure with a high resolution transmission electron microscope. The results were: the particle size distribution and the microcrystal structure of the soot particulates is little different for the cooled freezing method and room temperature sampling. The typical layer plane structure which characterizes graphite carbon is not observed in the exhaust of diesel engines, but some particulates display a somewhat similar layer plane structure. The structure of soot particulate is a turbostratic structure as the electron diffraction patterns show polycrystals. The soot particulates in the combustion chamber is similar to exhaust soot particulates.

Blue smoke and HC emissions from a direct injection diesel engine increase gradually during long idling operation (for a few hours). The extent of this increase depends on the injection nozzle specification and engine operating conditions. The accumulation of carbon deposits on the nozzle tip and combustion chamber wall will depend on these factors. Since the carbon absorbs fuel well, low volatility components can not evaporate during the combustion period and the unburned fuel emissions increase over time. This tendency changes according to fluctuations of spray shape and cylinder to cylinder fuel quantity variations.

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.

Exhaust particulate in diesel engines is affected by fuel properties, but the reason for this is not clear. Interest in using low-grade fuels in diesel engines has made it necessary to understand the particulate formation mechanism and factors to decrease it. Particulate formation has been reported to start with thermal cracking of the fuel to lower boiling point hydrocarbons followed by condensation polymerization and production of benzene ring compounds; the formation of particulate takes place via polycyclic aromatic hydrocarbons. This report investigates the amount and configuration of particulate with a fluid reaction tube and in a nitrogen atmosphere, and analyzes polycyclic aromatic hydrocarbons (PAH) of fuels with different molecular structure and carbon number.

Exhaust particulate in diesel engines are affected by fuel properties, especially the aromatic hydrocarbon content and distillation properties, but the reasons for this are not clear. The process of particulate formation has been reported to start with a thermal cracking of the fuel to lower boiling point hydrocarbons followed by condensation polymerization and production of benzene ring compounds; the formation of particulate takes place via polycyclic aromatic hydrocarbons. The fuel properties affect diesel engine particulate because the thermal cracking and condensation polymerization of various fuels are different.

A critical factor in improving performance of crankcase-scavenged two-stroke gasoline engines is to reduce the short-circuiting of the fresh charge to the exhaust in the scavenging process. To achieve this, the authors developed a reciprocating exhaust control valve mechanism and direct air-fuel injection system. This paper investigates the effects of exhaust control valve and direct air-fuel injection in the all aspect of engine performance and exhaust emissions over a wide range of loads and engine speeds. The experimental results indicate that the exhaust control valve and direct air-fuel injection system can improve specific fuel consumption, and that HC emissions can be significantly reduced by the reduction in fresh charge losses. The pressure variation also decreased by the improved combustion process. CRANKCASE SCAVENGED two-stroke gasoline engines suffer from fresh charge losses leading to poor fuel economy and it is a reason for large increases of HC in the exhaust.

Extensive experiments were conducted on a low emission DI diesel engine by using Dimethyl Carbonate (DMC) as an oxygenate fuel additive. The results indicated that smoke reduced almost linearly with fuel oxygen content. Accompanying noticeable reductions of HC and CO were attained, while a small increase in NOx was encountered. The effective reduction in smoke with DMC was maintained with intake charge CO2, which led to low NOx and smoke emissions by the combined use of oxygenated fuel and exhaust gas recirculation (EGR). Further experiments were conducted on an optically accessible combustion bomb and a thermal cracking set-up to study the mechanisms of DMC addition on smoke reduction.

This paper presents results of experiments to reduce smoke emitted from direct Injection diesel engines by strong turbulence generated during the combustion process. The turbulence was created by jets of burned gas from an auxiliary chamber installed in the cylinder head. Strong turbulence, which was induced late in the combustion period, enhanced the mixing of air with unburned fuel and soot, resulting in a remarkable reduction of smoke and particulate; NOx did not show any increase with this system, and thermal efficiency was improved at high loads. The paper also shows that the combination of EGR and water injection with this system effectively reduces the both smoke and NOx.

The blue and white smoke (cold smoke) emitted from diesel engines during warm up at low temperatures and idling conditions contains pollutant gases which irritate eyes and nose, and reductions in this irritating, odorous gas have become important with the increasing numbers of DI diesel engine vehicles. To assess the blue and white smoke a qualitative assessment method is necessary, though, there are no simple and exact measuring methods. In this study a new assessment method using a digital camera and photo analysis system with a computer is introduced. With this method the luminance of the cold smoke is displayed as 8 bit data, and a quantitative evaluation is simple, when the influence of sunshine is corrected for the smoke luminance. This paper describes the correction method for the sunshine illumination and the technique for taking the photographs.

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.

Since there is a trade-off relationship between NOx and particulates in exhaust gas emitted from a diesel engine, simultaneous reduction of the amounts of NOx and particulates in a combustion chamber is difficult. However, the amount of particulates produced in the combustion process could be reduced in a state of almost complete combustion, and the amount of NOx produced during the combustion process could be reduced by the use of a catalyst and reducing agent in the exhaust process. It has been demonstrated that the use of ethanol as a reducing agent on a silver-base catalyst in the presence of oxygen is an effective means for reducing NOx, although the mechanism of the reduction has not been elucidated. Therefore, in the present study, an NOx-reduction apparatus was conducted, and model experiments on NOx reduction were carried out in an atmosphere simulating exhaust gas emitted from a diesel engine and at the same catalyst temperature as that in a combustion chamber.

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.

This study investigated the odorous components in the exhaust of DI diesel engines. The complete products of combustion are H2O and CO2, which have no odor. Therefore, other products of incomplete combustion like unburned fuel components, partially burned components, cracked products from thermal cracking and others are thought to be responsible for exhaust odor. The THC in the exhaust is the result of incomplete combustion. This study measured THC in the exhaust, and a good correlation was found between THC and exhaust odor at different engine conditions. The low boiling point hydrocarbon components, especially CH4 in diesel exhaust were found to show a good correlation with exhaust odor. Aldehydes in exhaust gases correlate with exhaust odor very well and among the aldehydes, formaldehyde is found to be the most important component in causing irritating odor. The other part of this study is devoted to the improvement in the odor assessment used for DI diesel engines.

Direct injection diesel engines emit a far more disagreeable exhaust odor at idling than gasoline engines, and with increasing numbers of DI diesel engines in passenger cars, it is important to promote the odor reduction research. High pressure injection in DI diesel engines promotes combustion and decreases particulate matter (PM) emissions, but injection pressures at idling and warm up are limited to 30∼40 MPa considering engine noise and vibration. In this pressure range, a part of the fuel adheres on the relatively cool combustion chamber walls and causes incomplete combustion, producing higher concentration of unburned HC and intermediate combustion components (aldehydes, other oxygenated compounds, etc.) with objectionable exhaust odors. To reduce the exhaust odor, oxidation catalysts are effective, but catalyst activity is poor at idling, when the exhaust gas temperature is low (about 100°C).