The performance and emissions of SI and CI engines are known to be very much related to the external load, throttle position and speed of the engine. But no books or literature are clearly explaining what is meant by the engine load. Can someone explain how to define load acting on an IC Engine?
The engine load basically determines the capacity of the engine to produce power. It is the force which resists the power produced by the engine. Every engine is designed for particular load called as rated load or maximum load at particular speed. Whenever the load on engine increases, the engine speed decreases. To compensate this loss in engine speed, more fuel is supplied to the engine.When the load is greater than rated load, we say that engine is overloaded. In overload situation, speed decreases than rated speed. At this point, engine's ability to produce rotational power or TORQUE decreases. This gives rise to the need for variation in speed and torque according to driving conditions which we call it as transmission or gears. For stationary engines, the load is provided by dynamometers such as eddy current, hydraulic or rope brake dynamometers etc. For vehicle running on road, various loads act on the engine such as wind resistance, gradient of the road, self-weight of the vehicle, weight of passengers and luggage etc. Engine load is sometimes referred as torque or brake power (BP), where we see variation of engine parameters versus BP. In this case, BP is taken as the input while in actual case, BP is the power output of the engine. This is because, BP varies proportionally with load.
Load is an external restraining torque being applied to the engine. For the case where the engine is operating at a constant speed, the load torque is equal and opposite to the drive torque being generated by the engine.
If the load torque is less than the drive torque, then the engine will speed up.
If the load torque is greater than the drive torque, the engine will slow down (and ultimately stall).
On an engine test bench a dynamometer is used to quantify the power produced by an engine. So when you say that the load on engine is increasing we are infact pointing to the power produced by engine to overcome the load. Now compare the case of a vehicle running on a level road and vehicle climibing a gradient. For a case when the engine speed is the same on both occassions on which condition you could consider that the vehicle has a load acting on it.
In the two cases you mention, the load on the engine when it's propelling a vehicle uphill is greater than when it's propelling the same vehicle at the same speed on the level road (you can confirm this by looking at the throttle position required in each case). They are both loads.
If you Google 'Road Load Equation' (or even look it up in a book!) you will see how the load in these two cases can be quantified.
The engine load basically determines the capacity of the engine to produce power. It is the force which resists the power produced by the engine. Every engine is designed for particular load called as rated load or maximum load at particular speed. Whenever the load on engine increases, the engine speed decreases. To compensate this loss in engine speed, more fuel is supplied to the engine.When the load is greater than rated load, we say that engine is overloaded. In overload situation, speed decreases than rated speed. At this point, engine's ability to produce rotational power or TORQUE decreases. This gives rise to the need for variation in speed and torque according to driving conditions which we call it as transmission or gears. For stationary engines, the load is provided by dynamometers such as eddy current, hydraulic or rope brake dynamometers etc. For vehicle running on road, various loads act on the engine such as wind resistance, gradient of the road, self-weight of the vehicle, weight of passengers and luggage etc. Engine load is sometimes referred as torque or brake power (BP), where we see variation of engine parameters versus BP. In this case, BP is taken as the input while in actual case, BP is the power output of the engine. This is because, BP varies proportionally with load.
Manifold absolute pressure is also another suitable parameter that indicates engine load for engine with throttled intake manifold.
Load for Internal Combustion Engine is Power Output, which is controlled via amount of fuel.
In SI Engine amount of fuel is controlled by changing throttle, varying throttle position at constant rpm, vary effective air flow, therefore to maintain A/F, the fuel amount is varied.
In CI engine, manifold is unthrottled, the load control is directly achieved by fuel injector timing and duration.
Although MAF (Manifold Air Flow Rate) sensors are employed sometimes for both CI and SI inorder to account for density changes and. Ambient effext. Bascially, its primary signifcance is max power achieved under given conditions.
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