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The authors of this article reported in the previous paper[1] that the employment of oxidation catalyst was superior to the fuel modification such as reduction of T90 or poly-aromatic hydrocarbons in the improvement in exhaust emission reduction effect, as a part of approach to reduce diesel exhaust emissions based on fuel modification. In this paper, the exhaust emission reduction effect of a mixed diesel fuel containing 10% di-ethylene glycol di-methyl ether (DGM), which is an oxygenated fuel, in diesel fuel was evaluated, and the reduction effect was also evaluated with oxidation catalyst equiped engine. As the result, the THC, CO and PM reduction effect of DGM was clarified and further great PM reduction effect of the combination of DGM and oxidation catalyst was clarified.

Effects of fuel properties, in terms of the 90% boiling point (T90) and the polycyclic aromatic hydrocarbon (PAH) content, as well as oxidation catalysts on diesel exhaust emissions have been examined using three direct injection (DI) diesel engines and two diesel passenger cars equipped with oxidation catalysts. The diesel emission tests using two series of test fuels, one for examining the effects of the T90 and another for polycyclic aromatic hydrocarbons, have indicated that total hydrocarbons (THC) and particulate matter (PM) decrease as the T90 is reduced. PM and THC were also found to be on a declining trend with a decreasing content of polycyclic aromatic hydrocarbons. The extent of these effects of fuel properties on exhaust emissions varied with engine and car models, and appeared to be smaller in engines or cars having lower exhaust emissions.

We conducted a study of the effects of engine technology and fuel properties on diesel exhaust gas emissions. The effect of fuel properties on exhaust gas emissions was examined using four D.I. diesel engines equipped with an oxidation catalyst, high-pressure injection, turbocharger and natural aspiration fuel charging. In addition, oxidation catalysts were installed on the two turbocharged (T/C) and natural aspirated (N/A) engines to examine their effects on reducing exhaust emissions. As a result, it was found that the installation of oxidation catalyst clearly had an effect on reducing the levels of hydrocarbons (THC), carbon monoxide (CO) and particulate matter (PM). The high-pressure injection engine was found to have a low level of PM and not be affected by the type of fuel. It was clearly shown that engine technology has a greater effect on reducing exhaust emissions than fuel properties.

The effect of the fuel properties on diesel exhaust emissions was investigated using a commercial DI diesel and a prototype diesel engine with fuel jet impingement(OSKA--DH). The new type of diesel engine has a unique concept for the mixture formation process and is regarded as a clean diesel engine. Four types of fuels were prepared to investigated the effect of fuel properties such as cetane number, composition, oxygen content in fuel and oxygenate type on exhaust emissions for both of the engines. The decrease in cetane number caused an increase in NOx and a decrease in PM for the DI diesel engine because of the long ignition delay. However, in case of the OSKA-DH engine, a decrease in cetane number seldom caused an increase in PM emission. Although NOx and PM from aromatic fuel were higher than those from paraffinic fuel, the fuel effect for the OSKA-DH engine was smaller than that for the DI diesel engine.

A cold flow index of automotive diesel fuels in Japan has been investigated, from the view point of the fuel system configuration of diesel vehicles, by a task force study organized by the Japan Petroleum Institute. The results of the study are as follows; 1. The Cold Filter Plugging Point (IP 309, JIS K 2288) was found to be an excellent index of cold flow properties of automotive diesel fuels for the operability of Japanese diesel vehicles. 2. CFPP values for cold operability limits for the fuels at minimum ambient temperatures were established in the range from −5° to −30°C. 3. A rig tester simulating the cold operation of the most sensitive vehicle at ambient temperature was very effective in evaluating the cold flow properties of automotive diesel fuels.