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The purification performances of some kinds of catalytic converters ( Pt, Rh, Pd, Pd/Rh, Pd/Pt, Pt/Rh/Pd, Pt_Pd and Pd_Cu) were investigated to select suitable catalytic converters for natural gas fueled automotive engines. Pd series catalysts showed better performance among the noble metal catalysts for oxidation of unburned methane in exhaust gas. The optimum loading of Pd catalyst is the range of 1.6 to 3.2 g/L. The dual-bed catalyst, Pt_Pd, consisting of a Pt catalyst in the front and a Pd catalyst in the rear, showed a performance better than Pd series catalysts. When aged to an accumulated running distance of 50000 miles, the catalytic activity of the Rh catalysts is much reduced, but those of Pd and Pt catalyst are affected little by aging. The aged Pd/Rh catalyst showed superior emissions' purification performance at the stoichiometric condition, but poor at lean mixture conditions.

The purification performances of catalytic converters (Pt, Rh, Pd, Pd/Rh, Pt/Pd, Pt/Rh/Pd, Pt̲Pd and Pd̲Cu) were investigated to select suitable one for newly developed liquified natural gas(LNG) fueled vehicle. Two types of the construction of the catalytic converter, single-bed type and dual-bed type using two different catalysts in series, were used. A natural gas engine that has been modified the 3 cylinder gasoline spark ignition engine of 0.55 liter displacement equipped with newly developed manifold injectors was used for the investigation. The conversion performance of the exhaust gas at different catalyst temperatures was discussed with main emphases on methane conversion. The durability of the catalyst and the optimum loading of Pd catalyst were also investigated. To understand the suitable operating condition for the developed LNG engine, the effect of air excess ratio and engine load were examined.

A new model to describe diesel combustion process has been developed. In this model diesel combustion field is divided into two zones, premixing and combustion. Turbulent mixing process is described by the stochastic approach in each zone separately. Comparison of calculations with experimental results showed that this model can predict the entire course of heat release and nitrogen-oxide formation precisely, under wide-spread conditions. Two-dimensional flame temperature distributions in the combustion field by the two color method were compared with simulation results. Both the measured and the calculated flame temperature distributions showed good agreements with each other. In the diesel combustion process, the injected fuel mixes with air entrained inside the spray. The mixture is thus formed, and ignites at several points. Random expansion of flamelets accelerates both mixing and combustion. Following this, fairly moderate diffusion combustion proceeds.

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.

Experiments have been conducted to investigate the inhibitory effect of the catalytic reaction of methane and the formation of formaldehyde in the presence of NO. With precious metal catalysts, the presence of NO showed an inhibitory effect on the methane oxidation and caused the formation of formaldehyde. In the absence of oxygen, however, formaldehyde was not produced in the catalytic reaction of methane and NO. Maximum formation of formaldehyde was about 0.6 % of NO with the Pt and Rh series catalysts. N2O formation is similar to the formaldehyde formation from the catalytic oxidation of methane in the presence of NO.

An automobile dissociated methanol gas fueled spark ignition engine along with a cold starter and an exhaust dissociator for the engine was developed. The engine was tested for its cold startability, performance, fuel consumption and exhaust emissions to assess its applicability to automobiles. The cold starter reforms the rich alcohol fuel mixture into dissociated methanol gas through a bubbling process at a cold start and during warmup. This starter allows to start the engine at ambient temperatures as low as −15°C, while resulting in reduced undesirable emissions. The exhaust dissociator dissociates methanol into hydrogen and carbon monoxide utilizing the waste exhaust heat. The engine fueld with liquid and dissociated methanol had a thermal efficiency better by about 20 percent than that fueled with gasoline, and gave exhaust emission levels similar to those of gasoline engines. It is clear that the engine system suggest a high potential for the use of methanol fuel in the future.

Ignition and combustion of methanol in a spark-assisted methanol diesel engine were studied for the purpose of developing such an engine that is practical for actual vehicles. It became clear through investigations on combustion of methanol in a spark-assisted methanol diesel engine that methanol combustion proceeds mainly by flame propagation. Based on this finding, effects of such parameters as the injection direction, ignition position, ignition energy, compression ratio, injection timing and ignition timing were studied to obtain optimal conditions for methanol combustion. It was found through such studies that it is effective to form the mixture upstream of the spark, plug relative to the swirling direction and increase the inductive component of the ignition energy to achieve a high ignition stability.

A dissociated methanol fueled passenger car has been developed which shows improved transient driving and exhaust emission performance. In order to improve the transient performance, a mountable engine control unit, a new exhaust dissociator and a dissociated methanol flow control valve were developed among others and examined. The new exhaust dissociator has a extended heat transfer surface area and double injector to improve transient response and heat exchange efficiency. The dissociated methanol flow control valve which is controlled by intake manifold pressure works as a compensator for delayed dissociated methanol at transient driving. The high thermal efficiency and low exhaust emission level was observed for the transient driving as well as steady state driving.

In recent research, decreasing oil consumption and using a synthetic oil have been shown to be effective methods of reducing smoke emissions. However, the investigation of the constituents of white smoke and its environmental effect on humans have not been undertaken. The purpose of this investigation is to clarify the characteristics and compositions of white smoke and to analyze its environmental effect on humans using Ames test, and to evaluate a control for reduction of emitted matter by steady-state engine tests. Emitted matters(EM) from synthetic oil is less than that of semi-synthetic and mineral oils under the same test conditions. Emission after treatment resulted in the lowest EM when simulating the results of the ISO 6460 test, which results showed a decrease to about 1/10. EM from two-stroke engine mainly consists of unburned engine-oil and more than 95 % of EM is soluble organic fraction (SOF).

Characteristics of mass emission of unburned Oil-Particulate Matter and polycyclic aromatic hydrocarbons from two-stroke scooter were investigated. The tests were carried out under with and without oxidation catalyst and various air-fuel ratio ranging from 12 to 16 at 50:1 of fuel-oil mixing ratio for easy sampling. Unburned Oil-Particulate Matter and 4- to 7-rings polycyclic aromatic hydrocarbons were trapped on filter. These compounds were analyzed by high performance liquid chromatography with fluorescence detector. Mass emission of polycyclic aromatic hydrocarbons and unburned Oil-Particulate Matter tends to decrease as air-fuel ratio which increased up to stoichiometric ratio. The highest conversion ratio of unburned Oil-Particulate Matter on the oxidation catalyst was 64%. Conversion ratio of polycyclic aromatic hydrocarbons increased as rings are smaller.