why does sifferent types of vehicle engine produce different exhaust emissions?

Answer 1

It is generally called efficiency
If an engine is set up correctly and run at its best efficiency, which is mot flat out or on tick over.
you will get the least emissions and the best MPG at a certain point

Answer 2

All your answers are from the chemistry salters open book paper, i advise you do not copy any of these as yahoo answers is a place where the examiners check first, and there is also the hundreds of students doing open book paper have already copied the same answers.