Clean Diesel Cars: Fact or Fiction?
When controversy arose in 2015 regarding clean diesel cars and engine emissions, it reignited the long-standing debate regarding diesel engines, fuel and pollution.
A variety of factors influence the amount of pollution any engine or fuel source produces. Diesel proponents point to the higher mpg ratings and more complete combustion attributed to diesel engines, and many potential buyers assume these factors automatically make diesel cleaner and more efficient.
Are clean diesel engines fact or fiction? Let’s take a look.
Carbon dioxide (CO2). Diesel fuel is less refined, denser and has a higher carbon content than gasoline. As a result, every gallon of diesel burned produces more soot and an average of 13% more CO2 than a gallon of gas. Because gasoline is more highly refined and more uniform in composition, it’s also easier to control and clean the exhaust before it’s released into the air. In fact gas engines have become so efficient, the air they expel is cleaner than the ambient air in most cities.
Nitrogen oxides (NOx). Diesel engines generate high levels of heat to achieve combustion, but heat also increases NOx production. These pollutants were at the heart of the emissions controversy, when independent tests indicated some diesel cars emitted up to 35 times more NOx pollutants than the established maximum level.
NOx contaminants increase airborne particulates, contribute to smog and encourage ozone to form at ground level. They’ve also been associated with asthma attacks, bronchitis, respiratory ailments and cardiovascular issues, which according to the EPA can lead to hospitalization and even death. The young, the old and those with pre-existing conditions are at greatest risk.
Sulfur. Diesel fuel tends to be high in sulfur, which produces more soot and a distinctive smell when it burns. Modern diesels do emit fewer sulfur-based pollutants due to advanced filters that trap sulfur-laden exhaust and the switch to ultra-low sulfur diesel (ULSD) fuel.
In Europe, close to half the cars on the road are diesel powered. Until recently European emission regulations focused almost exclusively on fuel efficiency and reduced carbon emissions, two criteria modern diesel cars have been explicitly engineered to address. In the US, less than 5% of cars are diesel, in part because vehicles must meet a broader range of strict standards designed to improve overall air quality as well as mileage.
There’s no doubt about it. Modern diesels are cleaner than ever before, but there’s room for improvement and new technologies are in the development pipeline. In the meantime, diesel carmakers are working to find ways to maximize fuel efficiency, reduce emissions and sustain performance to overcome the same challenges all auto makers face.