1.   By the time we reach Soho, our engine is emitting oily smells and making puzzling sounds.

2.   These are just the conditions that cause gasoline engines to emit relatively high levels of pollutants.

3.   Infrared detection is also difficult because its turbofan engine emits little heat.

4.   This nearly exhaust-free engine emits one-tenth the harmful gases accepted internationally as standard vehicle pollution.

5.   Two-stroke engines generally emit more smoke than four-stroke engines.