This is the story about the differences between diesel and gasoline engines: Diesel engines burn diesel fuel and gasoline engines burn gasoline.
Short and sweet, eh?
Actually, there’s quite a bit more to the story.
Different ways of igniting the fuel
Outside of differences in the fuel used, the most notable difference between diesel and gas engines is the way each ignites the fuel.
Diesel engines compress air in the combustion chamber until the temperature of the air increases enough to ignite the fuel (sprayed into the combustion chamber by the injector). Gasoline engines, on the other hand, use spark plugs that ignite a mixture of fuel and air at just the right time. In the engineering world, we describe the methods of ignition as compression ignition and spark ignition.
So, is that enough, or are you interested in more? If so, keep reading.
Diesels = more durable construction
Diesels are low-rpm, high-torque engines built to last much longer, in general, than gasoline engines. Engineers typically use bigger, heavier and stronger components since diesels are largely designed to work – and work hard.
It’s not uncommon to get 300,000 miles out of the diesel engine in a turbo diesel pickup and 1 million miles out of a diesel engine in an over-the-road truck. Impressive, but even more so when you consider those trucks are pulling or hauling heavy loads.
Modern diesel engines in turbo diesel pickups are typically rated at 400-plus hp and 900 ft. lb. of torque. An over-the-road truck engine can make more than 600 hp and 2,000-plus ft. lb. of torque. Those are huge numbers when compared to the typical big-block gasoline engine’s 400 hp and 500 ft. lb. of torque. True, horsepower is similar, but diesel engines excel at producing torque. And if we know anything about pulling and hauling, torque rules.
Turbos and direct injection
So we’ve established that the diesel engine is a big, bad, powerful long-lasting engine. But here are a couple more technologies that set diesels apart from gasoline engines.
Most diesel engines are equipped with a turbocharger and direct fuel injection.
Yeah, I know; you’re saying, “But wait…there are turbocharged, direct-injected gasoline engines out there, too.”
You are correct, but they’ve only entered the scene over the past couple years. The turbocharger jamming more air into the cylinder and the injectors spraying fuel directly into the combustion chamber help accomplish a lot of things.
• Increased power
• Reduced emissions
• Better fuel economy
• Easy-to-control injection timing
Now you see why the gasoline-engine world is copying the diesel-engine world.
So, why don’t we all drive diesels?
Right about now you’re asking, “Gee whiz, if diesel engines are so great, why aren’t we all driving diesel-powered vehicles?”
The answer is history and economy of scale.
Historically, diesels have a bad rep
Gasoline engines in general are much quieter, and most Americans enjoy listening to the radio in their vehicle without having to turn it up to blaring levels to drown out engine noise. Diesel engines have come a long way with recent technology to make them quieter. But it’s not likely they will ever be as quiet as gasoline engines.
Many people also still associate diesels with the sooty, smelly engines of years past. Thanks to modern exhaust treatment devices and the introduction of low-sulfur diesel fuel, today’s production diesels are much cleaner.
It’s hard to fit a diesel engine in a small car
Additionally, we are moving to smaller vehicles for improved fuel economy. It’s hard to take a large diesel engine and shrink it to fit today’s small vehicles. Yes, some auto manufacturers are playing in this realm, but small diesel vehicles are few and far between compared to their gasoline counterparts. Can you image trying to put a diesel engine into a Mercedes Smart Car? The engine would consume the car and you’d have to ride on the roof. A convertible of sorts, I guess.
Speaking of big, powerful diesels, check out our recap from the 2016 Diesel Power Challenge recap.