Discussion
The power developed and the exhaust gas temperature of a diesel engine compared to a spark ignition engine of the same size and running at the same speed respectively, are
Answer: D
Compared with the spark ignition engine, the diesel engine has lower power and lower exhaust gas temperature.
A diesel engine must run with considerable excess air to burn its fuel cleanly, so for the same swept volume and speed it burns less fuel per cycle than a petrol engine working near the chemically correct mixture. Its power output per unit displacement is therefore lower, which is why diesel engines are built heavier and larger for the same power.
Its exhaust is cooler because of the much higher compression and expansion ratio: the gases expand further and do more work before the exhaust valve opens, and the excess air dilutes them. The pairs with 'higher' get one or both of these comparisons the wrong way round.
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