Katsuyuki Ohsawa

Heat transfer enhancement in methanol steam reforming for a fuel cell

Abstract The catalytic methanol steam reforming reaction was investigated by numerical simulation and experiments. Methanol conversion ratio as well as carbon monoxide (CO), which poisons a typical polymer electrolyte fuel cell, increases in a tablet catalyst when temperature is elevated. There is a trade-off relationship between methanol conversion ratio and CO concentration. It was found that the reforming reaction is controlled by heat transfer at large methanol flow rate, where the trade-off relationship shifts to lower methanol conversion ratio and higher CO concentration. To improve the trade-off relationship, internal corrugated metal heater and external catalytic combustion heater were applied to enhance the heat transfer. Optimal cell density for the internal corrugated metal heater, which was about 9×10 5 cell/m 2 , was closely related with reaction parameters such as velocity, cell density, geometric surface area and hydraulic diameter. The catalytic combustion heater is larger than the internal corrugated metal heater in size. Both high methanol conversion ratio and low CO concentration were accomplished by heat transfer enhancement with the two techniques at large methanol flow rate.

LDA measurement of fuel droplet sizes and velocities in a combustion field

Abstract Laser doppler anemometry was applied to simultaneous measurement of fuel droplet size and its velocity in two kinds of continuous mini burners. Droplet size was determined from the scattered light intensity ( Ip ) and number of Doppler burst waves ( N ) that was required to correct the effect of different particle trajectories in the measuring volume. Prior to the experiments, calibrated lines for representative droplet diameters were made with regard to Ip and N . The two burners had different types of air assist fuel injectors. One had the injector with the swirler which provides assist air with a tangential velocity component. Another had the injector without the swirler and the air had no tangential component. These combustion flow fields were then compared. Downstream of the injector in both burners, Sauter mean diameter (SMD) varies as follows. In a combustion field it is larger than that in unburned condition and reaches a maximum, after which it decreases until all the droplet evaporate rapidly. These features agree with the results of numerical calculations for fuel droplet evaporation. In combustion fields, the SMD of the droplets from the swirler injector is about 10 μm smaller than that from the no-swirler injector. Therefore the droplets evaporate earlier than those from the no-swirler injector in the burner. Temperature measurement with a thermocouple shows that the temperature in the swirler-equipped burner is about 100 K higher than that in the swirlerless burner. The swirler provides a circular cone extension of droplets with high densities and high velocities. A higher temperature zone is formed just outside the cone end.

Spray vaporization model for multi-component gasoline

Abstract A multi-component droplet vaporization model for multi-dimensional calculation was studied in order to simulate the behavior of fuel droplets and mixture in a port injection gasoline engine. Calculation results for a single droplet show that the evaporation process of gasoline, which consists of more than 100 components, can be simulated using a model fuel composed of at least three representative species. Subsequently, three-dimensional calculations of flow and fuel spray for an actual engine intake port configuration were performed, using the developed multi-component vaporization model. It was shown that about 70% of the high-volatility component in injected gasoline flows into the cylinder, while about 70% of the low-volatility component stays in the intake port in the injected cycle.

Photographic and Three Dimensional Numerical Studies of Diesel Soot Formation Process

Soot formation process was examined by high speed photographs, using a single combustion 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: The main soot area is considerably smaller than luminous flame area, especially in the initial soot formation process; the main soot cloud first appears in the tip region of fuel-air mixture, downstream of ignition position a few submilliseconds after the ignition. It is the soot carried down from the ignition position by a gas flow; and temperature is more influential in soot formation, rather than fuel vapor concentration.

LDA Measurement of Gasoline Droplet Velocities and Sizes at Intake-Valve Annular Passage in Steady Flow State

The size, velocity and spatially relative frequency of fuel droplets were measured. The droplet size was determined from its scattered light intensity and the number of Doppler burst waves of an LDA signal. Intake port configuration effects and fuel injection effects on the droplet entrance manner into a cylinder were investigated using straight and swirl ports. The difference in manner was clarified to be due to the interaction between the airflow in the ports and the fuel droplets.

Reduction of exhaust emissions by air-jet turbulence in a DI diesel engine: application to an in-line 6-cylinder engine

In our previous study, it has been reported that exhaust smoke can be reduced in an experimental single cylinder diesel engine with the use of air-jet turbulence in the late combustion period. In this study, a device to generate air-jet turbulence in the late combustion period was applied to 6-cylinder DI diesel engine. The effect of parameters such as air-jet direction and timing were investigated. Smoke and particulates were reduced significantly without increasing NOx. Total particulates reduction by the air-jet in Japanese D13 mode is 37% for the constant NOx.

Euler Solver Using Unstructured Upwind Method.

The unstructured upwind method is proposed to solve compressible flow with complicated boundaries or an arbitrarily shaped mesh. The flux difference splitting (FDS) scheme and flux vector splitting (FVS) scheme, which are extended to the unstructured grid system, are compared. The Euler equation is discretized by the control volume method. All conserved variables are stored at the cell center. The MUSCL approach for the cell-centered unstructured grid is proposed to obtain higher-order accuracy. A three-stage Runge-Kutta method is used for the time stepping scheme. The present calculation methods are applied to two-dimensional front-facing step flows. The results demonstrate that the present MUSCL approach is effective to obtain high resolution, and the triangular mesh solver is comparable to the uniform orthogonal mesh solver. FDS gives slightly better resolution than FVS.

Catalytic combustion with practical liquid fuel.

The characteristics of catalytic combustion below 1000°C with gas oil and kerosene were measured using practical catalysts, Pd-Al2O3 or Pt-Al2O3. A one-dimensional steady-state combustion model was developed to predict the temperature distribution in the catalyst. The following results were obtained. Pre-heating of the mixture up to about 300°C was required to start the catalytic combustion. The fuel oxidation was controlled by the fuel diffusion from the mixture to the catalyst surface below about 700°C; the combustion efficiency was determined to be a function of the non dimensional number, Re·Sc·d/l. The gas-phase reactions were activated and combustion efficiency was increased at the burnt gas temperature higher than 700°C. The developed model was capable of predicting the combustion efficiency, the temperatures of the burnt gas and the catalyst.

A NEW FEEDBACK CARBURETOR WITH AIR JET COLLISION CONTROL

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 combination 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.