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Soot accumulation in diesel engine crankcase is the dominant factor which governs engine oil drain interval. So, efficient soot elimination from crankcase oil can be a practical way to achieve drain interval extension. Combination of high performance oil filter and low soot dispersancy oil results in an effective measure to trap soot efficiently. In this paper, the behavior of newly developed high performance diesel engine oil having low soot dispersancy is reported. Prior to oil development, an evaluation method of soot dispersancy in oil was elaborated. Based on relative viscosity defined as ratio of soot containing oil viscosity to soot eliminated oil viscosity, dispersancy parameter was determined. Oil dispersancy evaluated on this parameter agreed with the results obtained from particle size analyzer. Secondly, a method to obtain oil filter soot trap rate to total soot contaminated into crankcase (trap rate) was established.

Analysis results of used oils sampled from many engines operating in the field show that the most critical factor governing the limits of oil use is insoluble fraction concentration in oil. Hence, the authors developed a new oil and by-pass oil filter to increase soot trapping efficiency, so as to extend oil change interval. Soot trapping efficiency could be improved from 30% to more than 80% using a bigger oil filter with fine mesh and a newly developed low soot dispersancy oil. Engine lubrication performance of the new oil was compared to that of standard and commercial long-drain oils by conducting 300-hour endurance tests on an 11.7 liter direct injection, turbocharged and aftercooled diesel engine at rated output. Test results proved superior engine lubrication performance of the new oil. THE INTERVAL between lubricating oil changes for diesel engines is twenty to forty thousand kilometers, depending on engine manufacturers' recommendations (1)*.

The injection nozzle inclination angle affects the flow characteristics in nozzle holes. Stroboscopic photographs of instantaneous spray plumes show that the length of each spray plume is different. Test results show that the fuel quantities injected from the holes are remarkably less when the nozzle hole spray angle relative to the injection nozzle axis is smaller compared with others with the same hole diameter. Hence, the authors analyzed the flow characteristics in injection nozzles using a computational fluid dynamic technique. Calculation results show good qualitative agreement with experimental results. INJECTION NOZZLES are normally installed in a two-valve cylinder head with an inclination angle. As shown in Fig. 1, the spray angle of each nozzle hole is different in order to maintain the same impingement height against the piston cavity for each spray.

Several types of oxidation catalyst material are tested in repeated particulate emission measurements over the US HDD transient test procedure. Particulates are effectively reduced in the initial stage of the measurements. However, particulates tend to increase when repeating the measurements. This is believed to be caused by sulfate adsorption on the catalyst surfaces. Hence, oxidation catalysts are tested after stabilizing surface adsorption. Test results show that an oxidation catalyst which forms more sulfates is not effective in reducing particulates because the sulfate increase offsets the SOF reduction effect. An effective catalyst for particulate reduction is developed by suppressing sulfate formation.

The characteristics of a new diesel particulate filter material made of SiC were studied through engine tests in varying material properties, such as average pore diameter, and wall thickness. Compared to a conventional cordierite filter of the same size, particulate trapping efficiency is almost the same, and the pressure loss and the deterioration of fuel consumption can be reduced to about half with the optimum material properties. If the same pressure loss is allowed, the filter size can be reduced by 30%. Its good thermal conductivity prevents local temperature increases, which doubles the permissible amount of trapped particulates. As heat crack problems occurred in integral-type filters due to the high thermal expansion of SiC, a split-type filter having 49 filter segments with a square section was developed.

A heavy-duty, naturally aspirated diesel engine was converted into a turbocharged, aftercooled, compressed natural gas engine. Engine test results show that excess air ratio and ignition timing strongly affect NOx and THC emissions. Leaning the air-fuel mixture reduces NOx emission, but it increases THC emission and combustion becomes unstable above a certain excess air ratio. Retarding the ignition timing reduces both the NOx and THC emissions. Dual-plug ignition improves brake thermal efficiency. The NOx emission level can be reduced to meet the Japanese long-term emission regulation limit for heavy-duty gasoline engines with a sufficient safety margin by appropriately selecting the air-fuel ratio and ignition timing so as to keep the THC emission level below the regulation limit without using any after-treatment. The engine full torque characteristics were almost the same as the base engine throughout the engine speed range, while the maximum exhaust gas temperature was lower.

The effects of fuel properties on diesel engine exhaust emission characteristics are investigated using eleven kinds of fuel with varying levels of sulfur and aromatic contents. Exhaust emissions from three engines are measured over the new Japanese 13-mode cycle as well as the U.S. transient test procedure. Engine test results show that reducing the fuel sulfur content decreases particulate levels. This effect is more pronounced for engines that emit more SOF. Enriching the aromatic content with dicyclic and other polycyclic compounds increases particulate, NOx, CO, and THC emissions. This particulate increase is due to the increase of SOF. Accordingly, low sulfur fuel should be produced without increasing the aromatic content, otherwise the SOF increase will offset the particulate reduction effect of the low sulfur fuel.