Diesel engines are inherently more efficient than those that combust gasoline. A properly designed diesel engine will always do a better job than a gasoline-powered equivalent of converting heat into mechanical torque and power.
The heightened efficiency of diesel engines relative to those that are fueled by gas is an advantage, in general, when it comes to environmental impact. Because diesel engines combust less fuel in order to do a given amount of work, they tend to put less of a burden on the environment by default.
An Effective Solution to Black Smoke Produces Another Problem
This is particularly true of various substances that are thought to contribute the most to global-scale environmental challenges. Diesel engines that operate near the stoichiometric limit of the associated heat-engine cycle, though, are prone to producing unpleasantly smoky exhaust that is heavy with soot and partially combusted hydrocarbons.
The solution to this formerly common problem is to instead run such engines at considerably leaner air-to-fuel ratios. Diesel engines that are tuned to tolerate especially lean fuel loads, however, end up generating harmful, though less-obvious substances of other kinds.
By far the most dangerous of these are the members of a family of compounds known as nitrogen oxides. In addition to contributing to the greenhouse effect, nitrogen oxides encourage the development of smog when broken down by the sun. Since lean-running diesel engines produce at least an order of magnitude more nitrogen oxides than those that combust gasoline, the environmental import of these facts is significant.
The Best Way to Reduce the Emission of Nitrogen Oxides
Fortunately, recent decades have seen the development of a number of technologies that can be used to help reduce the magnitude of this problem. Selective catalytic converters found in many vehicles can be adjusted to help break down nitrogen oxides as they pass through in a vehicle’s exhaust.
Many diesel-powered trucks and even some cars now include significantly more effective systems. When a substance known as “diesel exhaust fluid” is injected into an exhaust stream, it can neutralize nitrogen oxides with the help of the ambient heat. This solution is has been employed with success to clean up the emissions streams of millions of commercial vehicles.