Hiroshi Miyagawa

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.

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.

Ammonia as a hydrogen energy carrier and its application to internal combustion engines

Anhydrous liquid ammonia offers a considerable advantage over hydrogen in that it has a large volumetric energy density. The total amount of energy that would be expended for its production and transportation to consumers is estimated to be less than that for liquid hydrogen transportation, even if the lower heating value loss is considered. From a storage viewpoint, these advantages would be particularly beneficial to those vehicles carrying large amounts of freight.

Fundamental analysis on auto-ignition condition of a lubricant oil droplet for understanding a mechanism of low-speed pre-ignition in highly charged spark-ignition engines

This article presents a study of the mechanism that the lubricant oil droplet initiates low-speed pre-ignition in highly boosted downsized gasoline engines. Low-speed pre-ignition is a phenomenon that the fuel–air mixture ignites before the spark timing, leading to flame propagation that results in a heavy knock. The ignition of lubricant oil droplets is thought to be one possible mechanism for low-speed pre-ignition. However, the oil droplet ignition conditions are not yet well understood. First, the conditions under which a single oil droplet initiates the combustion of a fuel–air mixture were investigated using a rapid compression and expansion machine. When an initial droplet temperature was above 250 °C, the vaporized oil ignited before the gasoline–air mixture, in which case the combustion of the gasoline–air mixture around the droplet was initiated. The numerical results showed that the oil droplet temperature increases above 250 °C if the droplet is heated by burned gas remaining in the combustion chamber from the previous cycle. A direct-injection single-cylinder research engine was operated under the condition that no residual gas exists in the combustion chamber. In this case, no low-speed pre-ignition occurred even if gross indicated that mean effective pressure was 2.5 MPa. These results indicate that an oil droplet does not cause low-speed pre-ignition if any droplet flies into the combustion chamber unless it remains in the chamber over the exhaust stroke.

Numerical Simulation of Combustion Processes in Homogeneous and Stratified Charge Spark Ignition Engines

A three-dimensional simulation technique for stratified combustion process in direct injection gasoline engines is developed. The laminar flame speed for wide range of mixture equivalence ratio and EGR condition is modeled taking into account the reference temperature intermediate between unburned and flame temperature for chemical reaction. This new laminar flame speed model and the coherent flame model are incorporated into a CFD code. The calculated flame propagation process, heat release rate and exhaust emissions are validated by measurements including LIF technique. The good agreement obtained for various conditions shows the availability of this method.