I read that a researcher reported that :the torque decrease with the increase in the engine speed as a result of a decrease in the force on the piston and crankshaft . Can it be true?
Because the output power remain constant so The torque is inversely proportional to velocity
Olusegun D. Samuel
I assume that:
1. mass of injected fuel is consant
2. angle of start of injection is constant.
If so, the torque will decrase because of almost constant ignition delay. When the rotational speed is higher, a cylinder peak pressure is shifted towards later part of power stroke and all the p-V diagram is less and less beneficial. The other thing causing lowering of torque at higher rpm's will be higher mechanical losses in this range.
Hope this will at least partially help you.
The torque-speed characteristic peaks at the max-torque speed and torque falls if the speed is increased further. This is because of the inefficient filling in of fresh charge (limited by the intake valve timing) - at high speeds, there is insufficient time for intake and the ram effect of incoming charge is not fully utilised by the time intake valve close. Consequently, the energy release and cylinder pressures fall beyond the max-torque speed - probably this is what the researcher meant by less force on the piston and crankshaft. This is manifested as the reduction in brake torque.
I really appreciate your wonderful contribution, Dr. Saleel Ismail
usually, they have an optimum point in the middle. after that point, in a constant load which means that fuel quantity and air remain constant, an increase in speed of piston doesn't let fuel burn completely (decrease of time). so it causes a decrease in torque. before the optimum point, increase in speed causes an increase in torque.
Another possible reason for this is the increase in frictional power with increasing speed.
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