2007 年 32 巻 1 号 p. 41-46
In practical hydrogen fueled engines where hydrogen gas at high pressure is directly injected into the combustion chamber and consequent burns, it is impossible to identify the contribution of the energy of the hydrogen gas pressure to the engine output power. And, it is very important to know theoretically the contribution because the pressure of the hydrogen gas affects the system of the engines. It is also significant to whether the work obtained only by the direct injection into the engine without combustion, namely only by the pressure energy of hydrogen injected into the combustion chamber, can compensate the work needed to pressurize liquid hydrogen in the pump or not. If not, the work of the pump driving is supplied from the engine, decreasing the engine output power and the thermal efficiency.
By varying the direct injection pressure from 5 to 35 MPa and the mixture strength, namely the air-fuel ratio or air excess ratio, a simple theoretical thermodynamic study was carried out to clarify the contribution of the pressure energy of the hydrogen injected, the balance of the work needed for the pump driving and the work obtained by the direct injection. As a result, the followings have been found. The injection pressure studied here is above the critical pressure of hydrogen.
(1) There is the contribution of the energy of the hydrogen gas pressure to the engine output power. The contribution is small, varying from 1.61 % to 1.68 % of the combustion energy when the injection pressure varies from 5 MPa to 35 MPa.
(2) The work obtained by the direct injection can compensate the work needed to drive a liquid hydrogen pump. But it depends on the conversion efficiency of the electric generator.
In addition, the simple estimation study carried out to obtain the results of this paper will be explained.
