Pumping Losses in Spark Ignition(SI) Engines

An automobile engine has to pump in fresh air-fuel mixture during intake stroke and also to pump out exhaust gases during exhaust stroke. This requires energy by an engine to pump in and pump out gases.

Less Throttle Intake

During half or less throttle intake the pressure difference arises when the pressure inside intake manifold is less than atmospheric pressure. In this case piston has to work more to pump in gases due to larger difference in pressures(manifold and atmospheric).

Full Throttle Intake

At full throttle input or larger loads the pressure differnce is less or almost pressure inside the manifold is same as that of atmospheric pressure. So, in that case piston has to work less to pump-in fresh air-fuel mixture. Here pumping losses will be less. And here comes the benefit of Variable Valve Timing that by variable valve timing mechanism the exhaust valve early opens before BDC(Valve Lead) of the piston which releases residual gases and hence during exhaust stroke piston has to work less or piston puts less energy to pump out these gases.

The concept of pumping losses seems extremely benefial in automobile industry as because of this auto start/stop function was developed which stops the engine at lower loads and thus pumping losses are reduced. Moreover the concept of volumetric efficiency is linked to pumping losses as volumetric efficiency increase with the increase in air intake so pumping losses will be less. Due to this devices like turbochargers and superchargers are beneficial in lowering pumping losses.

How Pumping Losses Can be Reduced?

As all of us know that pumping losses affect the power, performance, and fuel consumption of an engine. Pumping losses refer to Work Done by an engine to pump in the fresh air. So here I will discuss how these losses are reduced by technologies like Variable Valve Timing(VANOS), VVT-i, i-Vtec, and Variable Valve Lift(Valvetronic) plus how the design of the engine has an impact on lowering these losses.

The Legendary technology of Valvetronic helps in reducing pumping losses as it eliminates the role of the throttle body. So, the throttle valve remains open and almost air pressure is equivalent to atmospheric pressure at the intake valve. So, in this case, pressure losses are less and the engine draws more air during intake stroke which in turn allows to increase compression ratio. Moreover, the engine has to do less work in pumping the air. This technology accomplishes the task of lowering emissions by lowering fuel consumption.

Vanos or Variable Valve Timing helps lowering pumping losses by adjusting camshaft timing. It adjusts the timing of the camshaft to pump in the air that is required according to power needs. Such as when less power is required it reduces the flow of air while during high requirement of power when the vehicle is accelerating it pumps in more air. Air intake is very important in lowering pumping losses like when an engine intake less air according to requirement it will increase pumping losses by lowering air pressure or by increasing the engine’s effort to pump in the air. On the other hand, if more air is input to the engine it will cause trouble in compression and expansion during compression and expansion stroke respectively.

Remember Both Valvetronic and VANOS works in conjunction with lowering pumping losses.

Turbocharging is another technique to lower pumping losses and increase the volumetric efficiency of an engine by increasing the amount of air intake by the power of exhaust gases this technology.

Conclusion

This concept should be explained to further understand the technoogy of BMW Valvetronic. The concept is extremely beneficial as it lead to further eliminating or minimizing the use of throttle body and also in the development of auto start/stop function in automobiles.