Hydrogen Combustion Engines Research Articles

NOx model development and validation with diesel and hydrogen/diesel dual-fuel system on diesel engine

In this paper, a common NOx model for hydrogen and diesel fueled combustion engines is developed and experimentally validated on a diesel engine with diesel and hydrogen/diesel dual-fuel operation system. The model is developed based on the simple measurement with the commonly used sensors situated on the engine system. NOx model is then calibrated with NOx sensor in diesel and hydrogen/diesel dual-fuel operation experiment with different engine variables, such as engine speed, engine brake power (equivalence ratio), hydrogen energy share ratio, injection timing and exhaust gas re-circulation (EGR). From results, it is observed that the model performed well in diesel engine with diesel fuel operation, injection timing and EGR with a single calibration factor on wider range of operating conditions. Moreover, NOx model has also shown satisfactory results with hydrogen/diesel dual-fuel combustion using a single calibration factor on a fixed operating condition (speed and brake power constant) with hydrogen ratio changes. The changes in calibration factor evident different fuel combustion properties and flame temperature kernel travel in cylinder changes for diesel and hydrogen fuel. Hence, finally, it can be stated that the developed NOx model can be used for diesel as well as hydrogen/diesel dual-fuel engines with simple calibration efforts.

Life cycle cost and sensitivity analysis of a hydrogen system using low-price electricity in China

To fully utilize low-price electricity including curtailed electricity (CE) and valley electricity (VE) in China, a hydrogen system, which can also be used for reducing peak electric power and raising the capacity factor of power supply equipment, is proposed as a solution for low-price electricity applications. The objective of the present study is to conduct a life cycle cost (LCC) analysis of hydrogen systems using low-price electricity considering three of significant application paths: 1) hydrogen is sold as a chemical material; 2) hydrogen fuels a polymer electrolyte membrane fuel cell (PEMFC) to drive an automobile; and 3) hydrogen is burned in a hydrogen combustion engine to output power. A sensitivity analysis of these hydrogen systems using either curtailed renewable electricity or VE in China is conducted. The LCC of hydrogen using CE in Path 1, Path 2, and Path 3 are $0.9700/kg-H2, $0.1226/kWh, and $0.1265/kWh, respectively. When using VE in Path 1, Path 2, and Path 3, the LCC are $1.5389/kg-H2, $0.1273/kWh, and $0.1384/kWh, respectively. The average retail price of hydrogen is $4.2/kg-H2 in China, so the technical path utilizing hydrogen as a chemical material (Path 1) appears to be the more economically viable path. Based on the sensitivity analysis of Path 1, reducing the equipment cost, improving the hydrogen purity to increase the retail price, and enhancing the electrolytic efficiency are critical and are suggested as future research topics. The impact of the loan ratio is also analyzed in this work.

Derivation and validation of a heat transfer model in a hydrogen combustion engine

Due to marked differences of material properties and combustion characteristics between hydrogen and carbon-based fuels, an increased heat flux inside the cylinder of hydrogen-fuelled internal combustion engines occurs. The present study aims for a simulation model that describes the wall heat transfer within the entire range of engine calibration possibilities. Conducted experiments on a hydrogen engine equipped with temperature sensors provide the base for the present study. Using the surface temperature method, highly resolved instantaneous surface heat fluxes can be identified. These measurements are compared with results from published heat transfer models that are originally developed for conventional fuels. As no satisfying result with these models can be obtained for the hydrogen engine, a modified heat transfer model is derived and validated based on the experimental data. Necessary developments on characteristic model features lead to a distinctive model for a hydrogen engine. It is demonstrated that the proposed model attains a consistently high prediction quality for a broad range of engine calibration variabilities.

On the applicability of empirical heat transfer models for hydrogen combustion engines

Hydrogen-fuelled internal combustion engines are being investigated as an alternative for current drive trains because they have a high efficiency, near-zero noxious and zero tailpipe greenhouse gas emissions. A thermodynamic model of the engine cycle would enable a cheap and fast optimization of engine settings for operation on hydrogen, facilitating the development of these engines. The accuracy of the heat transfer submodel within the thermodynamic model is important to simulate accurately the emissions of oxides of nitrogen which are influenced by the maximum gas temperature. These emissions can occur in hydrogen internal combustion engines at high loads and they are an important constraint for power and efficiency optimization. The most common heat transfer models in engine research are those from Annand and Woschni. These models are developed for fossil fuels, which have different combustion properties. Therefore, they need to be evaluated for hydrogen. We have measured the heat flux and the wall temperature in an engine that can run on hydrogen and methane. This paper describes an evaluation of the models of Annand and Woschni, using those heat flux measurements and assesses if the models capture the effect of changing combustion and fuel properties. The models fail on all the tests, so they need to be improved to accurately model the heat transfer generated by hydrogen combustion.

Improving thermal efficiency by reducing cooling losses in hydrogen combustion engines

Hydrogen can be readily used in spark ignition engines as a clean alternative to fossil fuels. However, the higher burning velocity and shorter quenching distance of hydrogen compared with hydrocarbons cause a larger heat transfer from the burning gas to the combustion chamber walls. Because of this cooling loss, the thermal efficiency of hydrogen-fueled engines is sometimes lower than that of conventionally fueled engines. Therefore, reducing the cooling loss is a crucial element in improving the thermal efficiency of hydrogen combustion engines. Previous research by the author and others has proposed the direct injection stratified charge as a technique for reducing the cooling loss in hydrogen combustion and shown its effect in reducing cooling loss through experiments in a constant volume combustion vessel. However, it is known that a reduction in cooling loss does not always improve thermal efficiency due to a simultaneous increase in the exhaust heat loss. This paper explains the relation between cooling loss reduction and thermal efficiency improvements by the direct injection stratified charge in hydrogen combustion engines.

Thermophysical Properties of Working Fluid and Heat Transfer in a Hydrogen Combustion Engine

A larger burning velocity and a shorter quenching distance for hydrogen as compared with hydrocarbons bring a higher degree of constant volume and a larger cooling loss from burning gas to the combustion chamber wall in internal combustion engines. Because of the large cooling loss, the reduction of the cooling loss are crucial for improving the thermal efficiency in hydrogen combustion engines. Empirical correlation for total heat transfer from burning gas to the combustion chamber walls are often used to calculate the cooling loss. However, previous research by the authors has shown that the widely used heat transfer correlation reported by Woschni cannot be properly applied to the hydrogen combustion. For this background, this research analyzes the relationship between characteristics of thermophysical properties of working fluid and heat transfer to the wall in a hydrogen-fueled spark-ignition engine.

3234 乱流熱伝達式を基にした水素エンジンのための壁面熱伝達式(S45-1 新燃料(1),S45 エンジンと新燃料)

Larger burning velocity and shorter quenching distance for hydrogen as compared with hydrocarbons bring larger heat transfer from burning gas to the combustion chamber wall in internal combustion engines. Because of a high cooling loss fraction by the large heat transfer, thermal efficiency of a hydrogen combustion engine is sometimes lower than that of conventionally fueled engines. Empirical correlation for total heat transfer from burning gas to the combustion chamber walls are often used to calculate the cooling loss in engines. However, previous research by the author et al. has shown that the widely used heat transfer correlation by Woschni cannot be properly applied to the hydrogen combustion even with adjusting the constants in it. This research tries to derive a new equation to describe the cooling loss in hydrogen combustion engines from the turbulent heat transfer equations for pipe flows.

Reduction of Cooling Loss in Hydrogen Combustionby Direct Injection Stratified Charge

Reduction of cooling loss from burning gas to the wall is crucial for improving thermal efficiency in hydrogen combustion engines. The research proposes the direct injection stratified charge to reduce the cooling loss in hydrogen combustion and analyzes its characteristics. The stratified charge in this research adopts direct fuel injection into lean mixture and spark ignition. The stratification is controlled by a fraction of directly injected fuel to the totally supplied fuel. A lowered temperature of the burning gas around the combustion chamber wall due to the leaner mixture by the stratification is expected to effectively reduce the heat transfer. The characteristics are analyzed in a constant volume combustion vessel by using measured pressure data and combustion gas compositions. Flame propagation is also observed for some cases.

水素エンジンにおける冷却損失と排気損失の関係(テクニカルフォーラム1 水素の製造・輸送・貯蔵・利用)

水素エンジンにおける冷却損失と排気損失の関係(テクニカルフォーラム1 水素の製造・輸送・貯蔵・利用)

New Heat Transfer Equation Applicable to Hydrogen Combustion Engines.

Equations to describe heat transfer from burning gas to the combustion chamber wall have been empirically derived from hydrocarbon combustion engines. Previous research by the authors analyzed the applicability of them to hydrogen combustion, and showed that the equations calculate lower cooling loss than experimental values. It was therefore concluded that a new heat transfer equation is necessary to describe cooling loss in hydrogen combustion engines. This research focused on the gas velocity term in the heat transfer equation and investigated new terms to replace it for better fit to hydrogen combustion. A new equation with a gas velocity term including rate of heat release was newly proposed and showed better application to hydrogen combustion compared to the widely used Woschni's equation.

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.

Heat Transfer from Burning Gas to the Cylinder Wall in a Hydrogen Combustion Engine.

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.