Toshio Shudo

Applicability of heat transfer equations to hydrogen combustion

Previous research by the authors showed that hydrogen combustion exhibits a higher cooling loss to the combustion chamber wall of an internal combustion engine compared to hydrocarbon combustion because of its higher burning velocity and shorter quenching distance. The high cooling loss means that reduction of the cooling loss is essential to establish a high thermal efficiency in hydrogen combustion engines. This research analyzed the applicability of equations to describe the heat transfer from burning gases to hydrogen combustion. The result shows that equations calculate a lower cooling loss than experimental values, and the use of correction coefficients does not accurately define the actual cooling rate. It is therefore concluded that the derivation of a new heat transfer equation for hydrogen combustion is necessary to improve the thermal efficiency of hydrogen fuelled engines.

Analysis of the degree of constant volume and cooling loss in a spark ignition engine fuelled with hydrogen

Abstract This study analyses factors influencing the thermal efficiency of a homogeneous charge spark ignition (SI) engine fuelled with hydrogen, focusing on the degree of constant volume and the cooling loss. The cooling loss from the burning gas to the cylinder walls in a homogeneous charge SI engine is quantitatively evaluated by analysing the cylinder pressure diagram and the exhaust gas composition. The degree of constant volume burning and the degree of constant volume cooling are also obtained by fitting the Wiebe function to the rate of heat release calculated using the cylinder pressure diagram. A comparison of combustion and cooling characteristics between hydrogen and methane combustion reveals that the cooling loss in hydrogen combustion is higher than that of methane combustion due to a thinner quenching distance and faster burning velocity for hydrogen combustion. It is also made clear that the higher cooling loss in hydrogen combustion results in lower thermal efficiency of hydrogen combustion as compared to that of methane combustion.

THERMAL EFFICIENCY ANALYSIS IN A HYDROGEN PREMIXED COMBUSTION ENGINE.

Abstract Hydrogen has higher flame velocity and shorter quenching distance than hydrocarbon fuels, and is supposed to have special characteristics in the combustion process of internal combustion engines. In this research, contributors to thermal efficiency in a hydrogen premixed spark ignition engine were analyzed and compared with methane combustion. Results showed hydrogen combustion had higher cooling loss to combustion chamber wall, and thermal efficiency of hydrogen combustion was mainly dominated by both cooling loss to combustion chamber wall and degree of constant volume combustion.

Influence of Hydrogen and Carbon Monoxide on HCCI Combustion of Dimethyl Ether

The authors have proposed a new HCCI combustion engine system fueled with DME and methanol-reformed gas (MRG) in the previous research. The research has shown high thermal efficiency over a wide range of the operable equivalence ratio in the system. MRG effectively controls the timing of the second stage heat release by the high temperature oxidation reactions of DME to expand the operable range. The MRG consists of H2 and CO. However, the effects of the two on the ignition of DME have not been separated yet. This research experimentally investigated each influence of H2 and CO on HCCI of DME. To separate the effects of H2 and CO on the ignition, HCCI combustion of DME/H2 and DME/CO are compared. The results of the analysis show that both H2 and CO have the effect of retarding the ignition. The results also show that H2 more largely affects the ignition in HCCI of DME than CO does.

Ignition Control by DME-Reformed Gas in HCCI Combustion of DME

Homogeneous charge compression ignition (HCCI) combustion enables higher thermal efficiency and lower NOx emission to be achieved in internal combustion engines compared with conventional combustion systems. Adjusting the proportion of two fuels with different ignition properties is an effective technique for controlling ignition timing in HCCI combustion. The authors have proposed a new HCCI combustion engine system fueled with dimethyl ether (DME) with a high cetane number and methanol-reformed gas (MRG) with a low cetane number in previous research. In the system, both DME and MRG are to be produced from methanol by onboard reformers utilizing exhaust heat from the engine. The research has shown high thermal efficiency of the system over a wide operable range of equivalence ratio. MRG effectively controls the timing of the second stage heat release by the high temperature reactions in HCCI of DME to expand operable range of equivalence ratio and engine load. This research newly proposes an HCCI combustion engine system fueled with DME and DME-reformed gas (DRG). In the system, just DME is stored in a fuel tank, and the DRG is to be produced by an onboard reformer utilizing exhaust heat from the engine. The system has an advantage of using the less toxic fuel over using methanol, though the heat recovery effect is lower than the previous system with MRG and DME produced from methanol. This research analyzes characteristics of HCCI combustion of DME and two types of DME-reformed gases. One type is a reformed gas by partial oxidation, and the other is by steam reforming. Both reformed gases contain hydrogen and carbon monoxide with low cetane numbers. The experiments are conducted by varying the proportion of the fuels and equivalence ratio. The overall thermal efficiency based on DME was also analyzed for ideal reforming conditions.

COMBUSTION AND EMISSIONS IN A METHANE DI STRATIFIED CHARGE ENGINE WITH HYDROGEN PRE-MIXING.

Characteristics of combustion and emissions in a methane direct injection stratified charge engine premixed with hydrogen lean mixture were analyzed. Results showed the combustion system achieved a higher thermal efficiency due to higher flame propagation velocity and lower exhaust emissions. An increase in the amount of premixed hydrogen stabilizes the combustion to reduce HC and CO exhaust emission, and increases the degree of constant volume combustion and NOx exhaust emission. The increase in NOx emission can be maintained at a lower level with retarded ignition timing without deteriorating the improved thermal efficiency.

NOx emission characteristics in rich–lean combustion of hydrogen

Abstract Characteristics of NO x formation in a gas turbine fuelled with hydrogen were analyzed with both an experimental and a numerical approach. This research experimentally investigated NO x reduction effect of rich–lean combustion in a coaxial burner. Hydrogen emits no Prompt NO even in rich mixture conditions, and can be more effective to reduce NO x in the rich–lean combustion system than hydrocarbons. The results show that the rich–lean combustion of hydrogen successfully reduces NO x emission compared with diffusive combustion. In the rich–lean combustion, hydrogen combustion has lower NO x emission compared to methane combustion, especially with larger equivalence ratio of richer side mixture. Calculations of NO x formation in the rich–lean combustion were also done employing the extended Zel’dovich NO formation mechanism.

STUDY OF PERFORMANCE IMPROVEMENT IN A DIRECT METHANOL FUEL CELL.

Abstract The direct methanol type system consists of simple and compact equipment, and is suited for automobile use. However this system possesses low power density and its internal resistance needs to be reduced. This research investigated characteristics of power output and thermal efficiency in a proton-exchange-membrane fuel cell directly fuelled with methanol solution. Some influences of catalyst amount and separator groove design on power output were also found.

Simultaneous reduction in cloud point, smoke, and NOx emissions by blending bioethanol into biodiesel fuels and exhaust gas recirculation

Abstract Palm oil has the important advantage of productivity compared with other vegetable oils such as rapeseed oil and soybean oil. However, the cold flow performance of palm oil methyl ester (PME) is poorer than other vegetable-oil-based biodiesel fuels. Previous research by the current authors has shown that ethanol blending into PME improves the cold flow performance and considerably reduces smoke emission. The reduced smoke may be expected to allow an expansion in the exhaust gas recirculation (EGR) limit and lead to reduced oxides of nitrogen (NO x ). This paper experimentally analyses the influence of EGR on smoke and NO x emissions with ethanol-blended PME. The results show that the combination of ethanol blending and EGR is effective in reducing NO x and smoke simultaneously without the thermal efficiency deteriorating. The smoke reduction can be attributed to an improved fuel—air mixing by an increased ignition delay owing to the low cetane number of ethanol and by a promoted fuel spray atomization caused by the low boiling point of ethanol. The increase in the oxygen content also leads to lower soot emission. The decrease in local equivalence ratio by ethanol blending was also suggested by the flame observation in which flame with high luminosity, high temperature, and high KL factor shrinks.

Influence of gas composition on the combustion and efficiency of a homogeneous charge compression ignition engine system fuelled with methanol reformed gases

Abstract A homogeneous charge compression ignition (HCCI) engine system fuelled with dimethyl ether (DME) and methanol-reformed gas (MRG), both produced from methanol by onboard reformers using exhaust heat, has been proposed in previous research. Adjusting the proportions of DME and MRG with different ignition properties effectively controlled the ignition timing and load in HCCI combustion. The use of the single liquid fuel, methanol, also eliminates the inconvenience of carrying two fuels while maintaining the effective ignition control effect. Because reactions producing DME and MRG from methanol are endothermic, a part of the exhaust gas heat energy can be recovered during the fuel reforming. Methanol can be reformed into various compositions of hydrogen, carbon monoxide, and carbon dioxide. The present paper aims to establish the optimum MRG composition for the system in terms of ignition control and overall efficiency. The results show that an increased hydrogen fraction in MRG retards the onset of high-temperature oxidation and permits operation with higher equivalence ratios. However, the MRG composition affects the engine efficiency only a little, and the MRG produced by the thermal decomposition having the best waste-heat recovery capacity brings the highest overall thermal efficiency in the HCCI engine system fuelled with DME and MRG.