Abstract
In this study, in order to convert a 2.4 L reciprocating gasoline engine into a hydrogen engine an experimental device for supplying hydrogen fuel was installed. Additionally, an injector that is capable of supplying the hydrogen fuel was installed. The basic combustion characteristics, including torque, were investigated by driving the engine with a universal engine control unit. To achieve stable combustion and maximize output, the intake and exhaust valve opening times were changed and the excess air ratio of the mixture was controlled. The changes in the torque, excess air ratio, hydrogen fuel, and intake airflow rate, were compared under low engine speed and high load (wide open throttle) operating conditions without throttling. As the intake valve opening time advanced at a certain excess air ratio, the intake air amount and torque increased. When the opening time of the exhaust valve was retarded, the intake airflow rate and torque decreased. The torque and thermal efficiency decreased when the opening time of the intake and exhaust valve advanced excessively. The change of the mixture condition’s excess air ratio did not influence the tendency of the torque variation when the exhaust valve opening time and torque increased, and when the mixture became richer and the intake valve opening time was fixed. Under a condition that was more retarded than the 332 CAD condition, the torque decreased by about 2 Nm with the 5 CAD of intake valve opening time retards. The maximum torque of 138.1 Nm was obtained at an optimized intake and the exhaust valve opening time was 327 crank angle degree (CAD) and 161 CAD, respectively, when the excess air ratio was 1.14 and the backfire was suppressed. Backfire occurred because of the temperature increase in the combustion chamber rather than because of the change in the fuel distribution under the rich mixture condition, where the other combustion control factors were constantly fixed from a three-dimensional (3D) computational fluid dynamics (CFD) code simulation.
Highlights
Interest in unmanned devices has been steadily growing in the aviation industry, and the demand for the research and development of unmanned aerial vehicles (UAVs) for communications and reconnaissance has been increasing
In the case of a high altitude long-endurance (HALE) UAV, on which this study focused, it was assessed that hydrogen with the highest energy density is the most appropriate and practical type of fuel
The change of the torque and efficiency according to the change of the ignition time at the excess air ratios of 1.3 and 1.25 was investigated under the condition by which the opening time of the excess air ratios of 1.3 and 1.25 was investigated under the condition by which the opening time of intake valve and the exhaust valve were fixed
Summary
Interest in unmanned devices has been steadily growing in the aviation industry, and the demand for the research and development of unmanned aerial vehicles (UAVs) for communications and reconnaissance has been increasing. The development of high-altitude, long-endurance UAVs that are suitable to reconnaissance and telecommunication operations, while maintaining a high altitude for a long period of time, is included in this category [1,2]. One of the most important technologies to be developed is the power source technology for UAVs. The use of high-energy-density fuels is essential for long-term storage at high altitude, and liquid hydrogen is the most promising among. The energy density of hydrogen fuel, which is approximately 120 MJ/kg [3], is much higher than that of conventional hydrocarbon series liquid fuels, which is approximately 45 MJ/kg.
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