The company has developed an engine and exhaust system that achieves Tier II Bin 5 emissions requirement without requiring additional filtering (aftertreatment) to remove nitrogen oxide (NOx). When used with a NOx aftertreatment, the company believes it can reduce emissions to meet the toughest emissions standards -- the Super Ultra-Low Emission (SULEV) and Tier II Bin 2 requirements.

Diesels that are on par in cost and cleanliness would be serious competition for gas-electric hybrids, and in the long run may be cheaper to operate because of the lower cost of diesel fuel (in many places) and the superior gas mileage.

Memories of dirty diesels and the difficulty in meeting air quality standards has kept diesels in the minority in the U.S., but Ricardo could change that. However, the company acknowledge that it won't happen right away.

"While there clearly remain many challenges in translating this research into high volume production solutions, this achievement provides significant new confidence in the future viability of the clean diesel in North America," said Dean Harlow president of Ricardo.