2014 Audi A7 TDI

Today, if you're a car company and you offer a diesel engine in this market, you have to go to great lengths to show consumers that it's less harmful to the environment than a gas-powered engine. That's why marketing types have come up with TDI Clean Diesel and EcoDiesel and BlueTec and so on, rather than just plain old "diesel." How much cleaner are today's oil burners, though?

Well, according to a study from the UK's Society of Motor Manufacturers and Traders, these torquey engines are cleaner than they've ever been. Diesel engines sold in Great Britain churn out 21 percent fewer pollutants than diesels sold in 2003. At the same time, fuel efficiency is up 27 percent compared to ten years ago.

Overall, the average diesel in the UK pumps out just 128.3 grams of carbon dioxide per kilometer, which is down nearly 30 percent since 2000, according to SMMT. It also marks the first time average diesel emissions have dipped below 130 g/CO2 per kilometer. To put that level of cleanliness into perspective, a gas-powered compact crossover like the Ford Kuga – our Ford Escape – produces 179 g/CO2 when fitted with a 1.6-liter EcoBoost four-cylinder.

"Motorists today benefit from much cleaner diesel cars than those that were on the market even ten years ago," Peter Fouquet, President of Bosch UK told HybridCars.com. "As diesel car sales continue to rise, we are focused on constantly innovating new technologies that help reduce emissions from diesel cars and make them cheaper to run."