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The size distributions of ultra fine particles in diesel exhaust were measured in a dilution tunnel at a high dilution ratio, and the results were compared with roadside measurements. The size distribution in diesel exhaust showed a single mode with a peak around 50 nm; in roadside atmosphere there was a bimodal distribution with peaks around 20 and 100 nm. Coagulation of diesel particles in the atmosphere was examined with an exhaust gas dispersion chamber. Coagulation of particles in the atmosphere and transient driving conditions of vehicle may cause the difference in size distribution between bench test results and roadside measurements.

Air Quality Modeling Working Group developed two models to evaluate effects of automobile emission reduction measures on air quality improvement: Urban Air Quality Simulation Model in which secondary aerosol formation processes have been incorporated, and Roadside Air Quality Simulation Model in which micro-scale traffic flow has been taken into consideration. Concretely, a model has been built up for estimating SPM concentration in ambient air in which high concentrated air pollutants have been contained during summer and winter. The model has been built up by using UAM (Urban Airshed Model) as base model, and the following modification has been made to the base model. First, ISSOROPIA (secondary inorganic aerosol equilibrium model) has been added to the base model, and a secondary organic aerosol formation/reaction model (SOA model) has been incorporated into the model.

Comparing with the previous Auto/Oil programs, the total plan and current status of the air quality modeling study in JCAP are presented. The total plan of air quality modeling study has the following characteristics: 1) Vehicle emission inventory program is developed by considering the original features of Japan. 2) Not only the urban air quality but also the road sides pollutants dispersion is evaluated. 3) The chemical reaction model for the secondary particulate formations is developed on the basis of the smog chamber experiments. 4) For the cost-effectiveness analysis of vehicle/fuel technologies, the output of the air quality modeling will be combined with the cost data of new vehicle emission reduction technologies As the first step, preliminary modeling studies are conducted to understand the overall tendency of the air quality change toward 2010 in Tokyo urban area.

Typical DI diesel engines operate with fuel injection taking place within a range of about 30 crank angle degrees before top dead center, at the end of the compression stroke. When injection takes place far earlier, at the beginning of the compression stroke, another form of combustion occurs, which we termed PREmixed lean Diesel Combustion, or PREDIC. With PREDIC operation, self-ignition occurs near top dead center and NOx emissions are drastically lower. When ignition occurs, the fuel-air mixture is thought to be nearly homogeneous, with only slight heterogeneity. Appropriate fuel spray formation is very important for successful PREDIC operation. Using a single-zone NOx formation model, calculations showed that the mean excess air ratio in the PREDIC combustion zone was 1.87, which resulted in very low (20 ppm) NOx emissions. Conventional combustion at the same conditions resulted in a mean combustion zone excess air ratio of 0.88.

Several methods to reduce ignition delay period were tested in combination with a high pressure injection and effects on combustion improvement were examined. It was found that the reduction of ignition delay does not give so much improvement at the usual injection timing before TDC, but when the injection timing is considerably retarded or when the original ignition delay is relatively long, shortening of the ignition delay is effective to reduce pre-mixed combustion and NOx emission. Further, assuming the combustion system which conforms to the 1983 Japanese regulation as the reference system, it was found that the combination of pilot injection and high injection pressure, simultaneously reduces NOx by approximately 35% and smoke by 60-80% without worsening the fuel economy.

Two dimensional flame temperature distributions in D.I. diesel engine with high pressure fuel injection were measured by the image analysis of high speed photographs based on two color method. Effects of injection pressure and nozzle hole diameter on flame temperature distribution were examined. The flame temperature in the case of high pressure injection is higher than that in low injection pressure. The higher flame temperature in high pressure injection results from the rapid compression of burned gases. The KL value which is an index of soot density in the combustion chamber decreases as injection pressure increases. The higher oxidation rate of soot at the later period of combustion may contribute to a soot reduction in the case of high pressure injection.

This paper reports on research works of ACE towards the most appropriate injection and combustion system for heavy-duty direct injection diesel engines. Selected items for the study are the effect of nozzle hole diameter, injection rate pattern, swirl ratio, and supercharging under high pressure fuel injection. According to those experimental results, the combination of over 150MPa injection pressure with controlled injection rate, smaller nozzle hole diameter, and quiescent combustion systems shows the best performance and emission. The mechanisms of the combustion improvement are discussed from the turbulent mixing viewpoint, including the results of combustion observation.

The characteristics of diesel combustion with high pressure fuel injection were investigated, using a naturally aspirated single cylinder engine and a high pressure injection equipment which can produce over 250 MPa injection pressure. Observation and analysis of combustion were performed using a high speed shadowgraph technique, with different injection pressures. In the case of high injection pressure in combination with smaller nozzle hole diameter, generation of soot in the combustion field is hardly recognized. Also by increasing injection pressure, ignition points tend to shift to the downstream of spray. Analysis of flame motion and turbulence intensity in the combustion field was performed using high speed direct photographs and image analysis technique by tracing flame luminosity distribution time history. By increasing injection pressure, an increase of turbulence intensity at the early stage of diffusion burning was observed.

A direct injection stratified charge engine using New Mixture Formation Technology (OSKA) has been developed. Experiments on a single cylinder engine, with methanol and gasoline fuels showed the following results: 1) With methanol, the maximum IMEP was 1.3 MPa and the best indicated thermal efficiency was 46 %. 2) With gasoline, the maximum IMEP was 1.16 MPa and the best indicated thermal efficiency was 43 %. Analysis of the cylinder pressure diagram showed the following results: 1) High indicated thermal efficiency was observed by low time loss. 2) A relatively short combustion duration was observed even if the engine was operated with an overall lean fuel-air mixture in the part-load condition. This fact suggests that a stratified charge was attained. 3) From observation of the heat release rate,it will be predicted that combustion is characterized by flame propagation.

For the purpose of developing direct injection heavy-duty methanol engines which surpass diesel engines in purformace, this paper first clarifies the methanol concentration around the spark plug for achieving a high ignition stability by sampling the gas near the spark plug using a sampling valve. The combustion process of methanol is then observed by the method of high-speed Schlieren photography to clarify the mode of methanol combustion. A new methanol DISC combustion system having a protrusion in the combustion chamber is devised based on such results. This study clarifies that the methanol concentration at the point of ignition for high ignition stability is in the range of 6 to 22 vol%. The methanol mixture burns by flame propagation so far as the compression ratio is on the order of 16.5.

Thermal efficiency of carbureted and injection engine was compared through thermodynamic cycle simulation. When the compression ratio is the same, the combined control carbureted engine in which the A/F ratio control method is used in the high load range and the throttling method is used in the low load range shows the highest thermal efficiency followed by the injection engine and the throttling carbureted engine. The thermal efficiency of the injection engine is lower than that of combined control carbureted engine because the temperature of gases in cylinder does not rise much due to stratified charge combustion. When the compression ratio of these engines is optimized, the thermal efficiency is the highest for the injection engine followed by the combined control carbureted engine. The thermal efficiency of the combined control carbureted engine is lower than that of the injection engine at high and low loads, but they are in the same level at intermediate loads.

A diesel engine with a dual-fuel (methanol-diesel) injection system has been developed, and the practicality of a prototype bus equipped with the developed engine has been confirmed. This study showed that methanol could be substituted for diesel fuel at the rates of 86 vol. percent in transient mode operation and 94 vol. percent in steady-state operation. Driving performance was equivalent to that of a conventional bus. Fuel economy of the dual-fuel injection engine was the same as that of a conventional diesel engine in steady-state operation, and decreased by about 9 percent in transient mode operation. The dual-fuel injection engine met the Japanese regulations on exhaust emissions stipulated in 1979. Exhaust smoke and particulate emissions were extremely reduced to the level of smoke-free operation.