An apparatus that controls a swirl ratio in a diesel engine for a motor vehicle includes a first intake port that directs a first airflow into a combustion chamber, and a second intake port that directs a second airflow into the combustion chamber. The first and second intake ports are arranged to direct the first airflow and the second airflow such that a desired swirl ratio is achieved in the combustion chamber.

A method of reducing NO.sub.x in the exhaust of a diesel engine having at least one combustion chamber by introducing NH.sub.3 into the diesel engine prior to a combustion event, at least some of the NH.sub.3 injected reducing the amount of NO.sub.x in the exhaust of the diesel engine, whereby the exhaust will contain an amount of NO.sub.x that is less than if no injection of NH.sub.3 was used, and will also contain an amount of NH.sub.3 that is less than the amount injected into the diesel engine, the rest of the NH.sub.3 being consumed during the combustion event and the reduction of NH.sub.3.