A small diesel engine could be great

Many avenues have been explored while looking for improved fuel economy. Ever since the CAFE standards for fuel efficiency became law, many changes have been made. One area that seems to have not received as much attention as it should is the use of a small diesel engine.

Fuel efficiency improvements


A small diesel engine could help keep up with CAFE expectations.

The automotive industry has been making many changes to the way things are done lately. Almost every auto manufacturer has a hybrid vehicle of some type, or in some cases a 100% electric. Along with these new vehicle options, they’ve changed the way they build traditional ICE vehicles too. Most new vehicles will now come with electric power steering, enhanced aerodynamics, TPMS, low rolling resistance tires, CVT, and computer programming that will improve efficiency.

small diesel engine turbo optional

A turbo will improve compression ratio.

Current gasoline engine setups

When it comes to internal combustion engines, it’s become popular to pair a small displacement engine with a turbo to get good MPG. Many companies offer a 1.8, 2.0, or 2.5 Liter engine with a turbo. The idea behind this is that the turbo can provide the additional power for accelerating and passing, while still getting good fuel efficiency at cruising speeds when the turbo isn’t needed. While this seems like a good idea, it’s still not perfect. This setup has introduced a whole new generation to the concepts of turbo lag and ceramic bearing failures.

ultra low sulfur diesel sign

Why not a small diesel engine?

What seems like a mostly overlooked option is the small diesel. A small displacement diesel engine can return great fuel efficiency numbers in turbo or normally aspirated configurations. Diesel cycle engine is more efficient for two main reasons.

– Firstly, diesel fuel has more energy in it per gallon than gasoline does. If you burn diesel it makes more heat than the same amount of gas.

-Secondly, diesels operate at higher compression ratios. It’s pretty much a rule that the higher your compression ratio is, the more efficiently your engine will burn fuel. A higher compression ratio leads to hotter and more complete combustion that allows the engine to get more power out of the same fuel.

Side-by-side, a gasoline engine and a diesel engine of the same displacement, the diesel will be roughly 30% more fuel efficient.

Drawbacks of a small diesel engine

There are a couple drawbacks to using a small diesel engine. Here are a couple bullet points to keep in mind if you are considering this type of vehicle.

  • Diesel fuel is more expensive than gasoline.

It’s mostly due to state fuel taxes, but diesel fuel can cost significantly more than gasoline in some states.

  • Emissions are an issue.

Many auto makers now use DEF as a pollution control device, but there are still particulate and other pollution concerns.

  • Diesel engines have a different power curve.

Diesels run at lower RPM, make less horsepower, and make more torque than a gasoline engine. Switching from a gasoline engine to a small diesel would require different gearing and transmission considerations.

While there are benefits and drawbacks to experimenting with a small diesel engine, it would be great if more car companies would try it. It’s a route that seems to show a lot of promise if more R&D was put into it and all of the little things were worked out.

Filed in: Diesel Engines
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