Search Results

The spray characteristics and inside flow of a marine diesel injector were investigated both experimentally and numerically. From the experiments, we observed that the penetration of the sprays in the early injection stage gradually increases. This phenomenon differs significantly from that of the small automobile diesel injector, in which penetration increases linearly with time. Using the momentum method to obtain injection rate measurements, we observed an injection rate spike at each injection event just after the injection began. The observed spray results show that the small portion of fuel remaining inside the nozzle from the previous injection event is ejected first, and then the main volume of fuel is ejected. Both fuels accumulate as spray droplets and gradually accelerate after the early injection stage. Numerical simulations of the injector's inside flow show that the fuel injection rate becomes saturated in needle lifts larger than 0.3 mm.

Methanol steam reforming, which is an endothermic reaction, needs some heating. Both methanol conversion ratio and carbon monoxide (CO) concentration increase when temperature is elevated. As CO poisons a typical polymer electrolyte of a fuel cell, the relationship between methanol conversion ratio and CO concentration is a trade-off one. It was found from preliminary researches that the reforming reaction speed is controlled by heat transfer rate at large methanol flow rate, where methanol conversion ratio becomes lower and CO concentration becomes higher. Therefore it is necessary to develop a new methanol reforming concept that provides stable combustion for heating and enhanced heat transfer for improving the trade-off relationship and making a compact reformer. Reforming catalyst using metal honeycomb support and a new catalytic combustion were applied to a new concept plate type methanol steam reformer, which is used in a fuel cell of 3 kW-class electric generation.

This paper presents the numerical simulation method to predict the deactivation process of three-way catalytic converters. Three-way catalytic converter's deactivation typically results from thermal and chemical mechanisms. The major factor of thermal deactivation is the sintering of noble metal particles, which is known to depend on the ageing temperature and the oxygen concentration in the exhaust gas. The chemical deactivation is mainly caused by the poisoning, which has two effects on the catalyst deactivation. One effect is the loss of the catalyst activity, which is expressed by reduced frequency factors of reaction rates. Another effect is the suppression of the noble metal sintering. Poison deposits prevent the noble metal particles from moving in the washcoat, assisted by the reduced thermal loading of reaction heats, which is caused by the loss of the catalyst activity. Modeling these deactivation factors, we propose the rate expression of noble metal sintering.

This paper deals with oxygen storage effect and NOx conversion reaction modeling. It was found that the oxygen stored in the catalyst increases with catalytic wall temperature and lean ( or rich ) depth from experiments using a well controlled flow reactor. Oxygen storage-release model (OSR model), incorporated with the NOx reduction reaction and THC or CO oxidation reaction, was established from the experimental results. Reaction rate parameters for three-way catalyst have been determined from the least data of flow reactor experiments using Evolutionary Algorithm. Transient temperatures and emissions are predicted using the developed OSR model and the determined reaction rate parameters for three-way catalyst, which are incorporated in the numerical algorithms used in the previous paper to predict flow and temperature field in a catalytic converter.

Three-dimensional numerical analysis of fuel liquid and mixture behavior in a port-injection gasoline engine is assessed by comparing calculations with measurements. The fuel mass distributed in the intake port and cylinder is measured using an engine with hydraulic valve and gas sampling system. The experimental results show that about half of the fuel mass per injection enters the cylinder, and the rest stays in the port. The difference of the mass fraction of injected fuel directly entering the cylinder is small between the cases of single pulse injection and serial injection. Therefore, three-dimensional calculation presupposing single pulse injection has difficulty in predicting the in-cylinder mixture formation process, although it can analyze the amount of fuel wetting the port wall. The calculations are performed for a port-injection engine, and the differences of fuel behavior with respect to swirl control valve opening and wall temperature are discussed.

Transient temperature and concentration distribution inside a catalytic converter during warm-up have been analyzed by experiments and numerical simulation. There is great maldistribution of species concentrations inside a converter during warm-up. Carbon monoxide (CO) and hydrocarbons (HC) have high concentrations in the exhaust gas passing through outer region cells because they are not converted due to low wall temperature. The effects of the noble metal loading pattern on conversion characteristics during warm-up have been investigated by numerical simulation. The effects of high-loading on improving conversion characteristics are saturated with the loading quantity of six times that of the base-loading. High-loading of the noble metal only on the frontal region (20 or 30mm. from the front face) has almost the same warming-up conversion performance as the uniform high-loading.

A new heating strategy for electrically heated catalysts has been developed which reduces power consumption while achieving the desired hydrocarbon conversion. The relationship between catalyst volume and power consumption is presented. Observations of catalytic reactions by a thermoviewer camera and mathematical simulations are used to optimize the heating pattern. Significant reductions in power consumption, while maintaining conversion efficiency, are reported by heating only the front face of the catalyst. However, prior to mass production additional work is required to improve durability, and reliability and to resolve manufacturing issues.

Quality control of gasoline constituents and its effect on the Intake Valve Deposits (IVD) has become a recent issue. In this paper, the effects of gasoline and oil quality on intake valve deposits were investigated using an Intake Valve Deposit Test Bench and a Sludge Simulator. The deposit formation from the gasoline maximized at an intake valve temperature of approximately 160 °C, and the deposits formed from the engine oil were maximum at approximately 250 °C. Therefore, the contribution of the gasoline or the engine oil appears to depend on the engine conditions. The gasoline which contains MTBE or ethanol with no detergent additive slightly increases the deposition amount. The gasoline with a superior detergent significantly decreases the deposition amount even when MTBE or ethanol is blended in the gasoline. Appropriate detergent fuel additive retards the oil deterioration.

It was shown in our previous study that the air-jet in the late combustion period reduces the diesel exhaust soot effectively. However, the plunger-pump type air-jet generator used in our previous study has a big power-loss. In this paper, the reduction of soot emission with a newly designed air-accumulation type air-jet generator is investigated using an experimental single cylinder engine. The optimum design parameters, such as the spring constant and the air outlet diameter, are examined experimentally. The effectiveness of the air-accumulation type air-jet generator for the reduction of soot and NOx emission is about a half of that of the plunger-pump type. It is confirmed that the disappearing speed of the luminous flame region accelerates with the increase of the heat-release in the late combustion period.

Soot formation process was examined by high speed photographs, using a single cumbustion diesel engine with a transparent swirl chamber. Fuel-air mixture and flames, and soot clouds were visualized by the schlieren method and the back-illuminated method, respectively. A three dimensional simulation program with soot formation and oxidation models was developed to clarify diesel soot formation processes. The models consist of several models previously proposed and partly improved in this study. Good agreement was obtained between calculated and experimental results. The following points were clarified through observation and numerical studies: (1) The main soot area is considerably smaller than luminous flame area, especially in the initial soot formation process. (2) The main soot cloud first appears in the tip region of fuel-air mixture, downstream of ignition position a few submilliseconds after the ignition.

A laboratory test simulator has been developed to analyze the intake-valve deposit formation mechanism. The characteristics of the deposits formed with the simulator were compared with those of the real engine deposits. This comparison verified that the simulator deposits ILLEGIBLE nearly equal to those of engines. The influence of each parameter such as valve temperature, oil or gasoline quality was tested individually using this simulator. The intake valve temperature influenced the location and quantity of the deposits. The deposit formation significant in the temperature range of about 0-350 °C. The high-boiling components of oil ILLEGIBLE increased the deposits. The increase oxidation products and the decrease of antioxidants in used oil caused a significant increase of deposits. The commercial premium gasoline in Japan containing practical detergents ILLEGIBLE down and decreased the deposits. Another premium gasoline affected the oil quality, in increasing the deposits.

In order to optimize air-fuel mixture formation in a small DI diesel engine, studies were conducted into the effects of combustion chamber shape and fuel spray impingement. Based on the findings of these studies, the shape of the combustion chamber was modified to induce complex air motion with high turbulence and fuel injection was carefully controlled to achieve optimum impingement intensity. As a result, the mixture formation process was greatly improved with a consequent gain in terms of engine performance. To clarify the reasons for this improvement in combustion, a three-dimensional calculation of the in-cylinder air motion was made. The behaviour of the spray and flame was observed using an endoscope. The new combustion system, named TOYOTA Reflex Burn system (TRB) thus developed has been adopted in production engines since August 1988.

A new type closed loop A/F control carburetor has been developed. In the carburetor, an air jet, a by-pass stream of an intake air flow, is made to collide with a fuel flow to suppress the flow rate. Studies were made of the basic features of the method such as fuel controlling capability and the factors affecting it from phenomenological consideration and schlieren observation. For comparison, three types of carburetors were prepared for the conbination of main and idle fuel circuits. In driving mode tests on a dynamometer, a new carburetor which employs the new method for the main fuel circuit, provides 30 % lower emission level than an air bleed control carburetor. Higher controlling frequencies were obtained for the new carburetors. The high controllability of the air jet collision control method is attributable to the smaller fluctuation in both the controlling air and the spouting fuel.