In IC engine 1. the ideal air capacity of a two-stroke engine is the mass of air required to concurrently fill the total cylinder volume at inlet temperature and exhaust pressure 2. with increase in air-fuel ratio beyond the value for maximum power, there is a fall in power developed and this fall is more with higher values of air-fuel ratio. 3. the volumetric efficiency of the engine depends on the design of intake and exhaust manifold. Which of the above are correct?

Option 3 : 2 and 3 only

The ideal air capacity corresponds to filling the displaced volume (piston swept volume) with fresh mixture at inlet temperature and exhaust pressure.

The variation power with air fuel ratio is shown in the graph below.

[ alt="F3 M.J Madhu 04.05.20 D4" src="//storage.googleapis.com/tb-img/production/20/05/F3_M.J_Madhu_04.05.20_D4.png" style="width: 375px; height: 248px;">

It is observed from the graph that with increase in air-fuel ratio beyond the value for maximum power, there is a fall in power developed and this fall is more with higher values of air-fuel ratio.

In the internal combustion engines the air-fuel mixture or only air is drawn during the intake stroke due to the low pressure environment created by the downward movement of the piston. This amount of intake air is usually less than the theoretical amount of air. The volumetric efficiency is the ratio of intake air and the theoretical capacity.

It is affected by the parameters such as compression ratio, engine speed air-fuel mixture temperature and the pressure ratio of exhaust to intake manifold.