For many, diesel engines are synonymous with black clouds of smog and heavy air pollution. These images are from a time, not long ago, that solidified diesel’s reputation as dirty burning fuel. A lot has changed since then, but diesel struggles to clean up its reputation. When compared to gas-powered engines, diesel has some surprising benefits.
Diesel is the hands-down winner in fuel economy
The cleanest gallon of fuel is the one that is never burned. Fuel economy is just as crucial for the environment as controlling emissions. No matter how clean a fuel burns, using less is always better.
This is where diesel is the clear winner. According to the National Center for Biotechnology Information, diesel engines are up to 25% more fuel-efficient than gas engines. Diesel fuel contains 13% more energy per gallon than gasoline.
If every full-size pickup in the U.S. were diesel, the country could save 500 million gallons of fuel. Diesel drivers pay 30% less in overall fuel costs. This savings, coupled with the higher power output of a diesel engine, is why so many commercial fleets choose this power train.
Cleaner fuel means lower emissions
Diesel fuel has been cleaned up considerably in the last ten years. Much like lead was removed from gasoline in the 1970s, a massive effort has been made to reduce sulfur in diesel fuel drastically. This sulfur was responsible for a large amount of particle matter emissions.
Ultra-low sulfur diesel (ULSD) has been standard since 2007, and improvements continue to be made. The sulfur used in this fuel has been cut by 97%, which saw soot emissions drop by 10%. Diesel has another clear advantage over gas, its refinement process.
The process of making fuel is messy and creates pollution concerns. Gasoline refinement is more complicated than diesel and produces more greenhouse gasses along the way. A cleaner refinement process paired with excellent fuel efficiency makes diesel a greener choice.
Where gasoline outperforms diesel
While huge improvements have been made to diesel fuel production and the engines that burn it, there’s a cleaner future ahead. New EPA standards seek to cut diesel emissions by another 40% by 2027. When these goals are met, diesel engines could beat gas in the one category where they still fall short, nitrogen compound emissions.
Six countries participated in a 2017 study of diesel engine pollution. The study found that gas-powered engines produce 10 times more particle matter emissions than diesel. Gas engines also found 40% more greenhouse gasses, but diesel NOx (nitrogen oxides) emissions are higher. Nitrous oxides are the one pollutant produced more by diesel engines.
The amount of nitrogen compounds produced by burning fuel directly correlates to the temperature reached. Diesel fuel burns hotter and therefore creates more NOx than burning gas. Exhaust emissions control systems can cut these emissions by up to 50%, but there’s room for more improvement.
There have been leaps in diesel emission improvement that don’t seem to impact public opinion. A single diesel truck from 1980 produces the same emissions as 60 trucks built by today’s strict emissions standards. Diesel has come a long way and should be thought of as a cleaner, non-renewable option.