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内容記述 |
In the previous reports, numerical calculation of power variation with compression ratio ε and air fuel ratio n, at sea level, and also those with altitudes from sea level to 15,000m under constant air fuel ratio n=0.9, and under constant compression ratio ε=4～9, in a naturally aspirated engine, were made by means of J. S. diagrams of air and combustion gases. This paper deals with changes in the theoretical brake mean effective pressures at sea level and at altitude, in a gear-driven supercharged engine, under constant air fuel ratio n=0.9, and under constant compression ratio ε=5～9. The supercharger is of course attached to the engine for the purpose of maintaining the engine power at altitude and also of increasing, positively, the engine power. In the supercharged engine, however, under constant air fuel ratio n and constant compression ratio ε, and under constant altitude z, that is, under constant atmospheric pressure P_z and temperature t_z, the indicated horse power LFP_z and brake horse power BFP_z varies, because the driving power for the supercharger changes with its pressure ratio P_s/P_z and with its efficiency, and because the boost pressure P_s and the temperature t_s in the suction pipe vary, while the effect of the back pressure also varies. In order, therefore, to make the relations of these factors clear in the first place, investigations were made of the effects of variation in the indicated horse-power, IFP_z, or the indicated mean effective pressure P_<miz>, with variations in the boost pressure P_s and temperature t_s and the back pressure P_z If we define the indicated mean effective pressure P_<miz> as that corresponding to area BCDE of the theoretical PV diagram of Fig.I, and if we take the mean effective pressure P_<mia>, corresponding to the area B'A'AB of Fig.I, now under consideration, separately, then under constant air fuel ratio n and under constant stroke volume of engine, and denoting the boost pressure and temperature of the suction pipe, back pressure ratio, compression ratio, and indicated thermal efficiency by P_<so>, t_<so>, (P_z/P_s)_0ε_0, and ηio, respectively, and its indicated mean effective pressure by p_<mio>, then for any P_s, t_s, P_z/P_s, ε, or η_i the indicated mean effective pressure P_<miz> is obtained by the relation of equation (20), which was investigated, theoretically, under the assumption that the indicated mean effective pressure P_<miz> is proportional to the mass flow of a new charge to the cylinder and the indicated thermal efficiency. The indicated mean effective pressure P_<mio> is found beforehand as an accurate standard-value by using J. S. diagrams of air and combustion gases, following which the value of P_<miz> is obtained by equation (20) merely as a fair accurate value, not using any J. S. diagrams. The brake horse-power BFP_z, or the brake mean effective pressure P_<mbz>, is then given by; P_<mbz>=P_<miz>-P_<mLz>-P_<msz>+P_<maz> where P_<mLz> is the mean effective pressure corresponding to friction and other lost horse-power, P_<msz> is the mean effective pressure corresponding to the driving power for supercharger, and P_<maz> is the mean effective pressure corresponding to the recovered power due to back pressure, as stated above. These values are calculated with the aid of equations (21), (23), and (25) respectively. Under these theoretical considerations, the power variation in a gear driven supercharged engine is calculated, theoretically, the compression ratios ε=5, 7, 9 being assumed, as also the rated altitude from sea level to 15,000m, the boost pressure from -400mm to +1,000mm Hg, and that the overall adiabatic efficiency of supercharger η_<ad>=0.65 and its polytropic index n=1.630. The power variations at sea level and above the rated altitude are also calculated theoretically. The following items are not taken into consideration in this paper. The effects of power variation due to the Fulcan coupling, which is often inserted between supercharger and driving shaft, and also that due to the exhaust gas driven superchanger. If the boost pressure P_s and its temperature t_s in the induction pipe are increased, the problem of detonation in the cylinder will have to be taken into account. |
SA4146526.pdf (4.1 MB)
