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Improvements in the fuel economy of passenger cars and trucks contribute directly to CO2 reductions. Recently low fuel consumption cars are being developed, however most cars are still old types. This study estimates the effect of new engine types, light weight cars, kinds of fuel, and running conditions on fuel economy and CO2 emissions with a new calculation method of fuel consumption. In this calculation method the fuel consumption and CO2 emissions are easily calculated from the indicated thermal efficiency and friction mean effective pressure for different engine types and sizes. By this method the overall fuel consumption and CO2 emissions from small passenger cars to heavy duty trucks were estimated for roads through the center of a small city. As a result, the influence of new type engines, light weight cars, fuel properties and driving patterns on fuel economy and CO2 was made clear.

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.

Modern small DI diesel engines are operated at high loads and high speeds. In these engines the spray spreading on the cavity walls during the main combustion is kept approximately constant at all engine speeds to optimize the air utilization. However, spray spreading on the wall during the early and late part of combustion changes with engine speed due to the changes in air motion. At the end of impingement much of the spray moves outside the cavity due to a strong reverse squish when the injection timing is set near TDC. This causes incomplete combustion of fuel and increase emissions of HC and soot. Therefore, the study of the behavior of spray affected by the reverse squish is very important. In this study the fuel spray development under high injection pressure and high gas charging pressure was investigated photographically in a small direct injection diesel engine with a common rail injection system.

This study investigated the influence of aldehyde and hydrocarbon components (HC components) on exhaust odor in DI diesel engines. Aldehyde is an important odorous group in exhaust, and it correlates well with exhaust odor at any engine condition. Formaldehyde (HCHO) in the exhaust has been identified as an important component causing irritating odor. Water-washing of exhaust gases does not trap HC components, while most of the odorous components are trapped with remarkable odor reductions. This indicates that the HC components in the exhaust have no direct effect on exhaust odor. However, the exhaust odor increases with increases in the concentration of the low boiling point HC components. This maybe due to the increase in intermediate odorous compounds like aldehydes, organic acids, or other oxygenated compounds in the combustion condition where the low boiling point HC components increase.

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).

Early stage combustion systems, with lean homogeneous charge compression ignition (HCCI), have been studied, with the intent to decrease the pollutant emission characteristics of DI diesel engines. Early stage combustion enables drastic reductions in both nitrogen oxides (NOx) and smoke emission, but the operating load range is restricted, due to combustion phenomena, such as unsteady combustion and knocking. In this study, we explored the possibility of broadening the operating load range in HCCI and reducing pollutant emissions using Dimethyl Ether (DME) fumigated through the intake pipe. However, the improvements in load range were found to be less than 0.1 MPa in brake mean effective pressure (BMEP), even when compression ratios were reduced and Methane with high octane number was mixed. Therefore, a DME premixed charge could be used only at light loads. At heavier loads a hybrid fuel system with a DME premixed charge and diesel fuel injection is necessary.

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.