Diesel and gas worlds apart

Long a favourite with Europeans, diesel power has far fewer fans in Canada, where it's more often associated with work trucks and tractor trailers. But that may change, as drivers come to appreciate diesel's better fuel economy ratings, and more automakers offer diesel-powered models.

While both fuels are made from crude oil, there are crucial differences between gasoline and diesel. Each requires a vastly different engine design,

"Gasoline does not have a lot of the heavier molecules that diesel has, and diesel doesn't have the volatile molecules that gasoline has," says David MacMillan, manager of fuels quality for Suncor Energy Products. "Diesel is a more dense fuel than gasoline. It's harder to set diesel on fire because it's not as volatile." MacMillan notes that diesel also boils at a higher temperature than gasoline.

The fuel is named for German engineer Rudolf Diesel. He wasn't impressed with early gasoline engines, which produced far more heat than power. His new engine design was patented in 1892, but wasn't really viable until 1923, when Robert Bosch developed an effective injection pump to spray the fuel in.

The big difference between gasoline and diesel engines is combustion. Both use the fuel to move pistons up and down, turning a central crankshaft; its spinning motion is eventually used to turn the vehicle's wheels. In a gasoline engine, fuel is mixed with air, compressed, and then set alight by a spark plug. A diesel engine first compresses air, which heats it up; the fuel is then injected, where it's ignited by the heat.

Diesels make most of their power at lower engine speeds, which is why they're ideal for trucks, which need to be able to move heavy loads from a standstill. They also get better fuel economy: diesel fuel contains about 10 per cent more energy than gasoline, and the engines are higher-compression and more efficient.

But they do have disadvantages. They tend to be heavier and more expensive than gasoline engines, their exhaust requires more treatment to meet emissions standards, and downtown dwellers frequently have trouble finding stations that sell the fuel.

There's also consumer reluctance among buyers who don't realize that the engines have improved considerably.

Unlike diesels in the past, they're now only marginally noisier than gasoline, there's no waiting for a glow plug to warm the engine before starting, they no longer spew sooty exhaust, and the new, ultra-low-sulphur diesel fuel that's been mandated in Canada since 2006 doesn't stink like the old fuel did.

There's also interest in biodiesel, a renewable fuel made from plants, animal fat or even algae.

"There are regulations that are coming into force in the next few years that will require renewable content in diesel," says Ken Mitchell, fuels engineer for Shell Canada. "It's relatively easy to make it from canola, soy, tallow, or anything like that."

The biodiesel fuel is rated by its content – B5 is 5 per cent biodiesel, 95 per cent petroleum biodiesel – and Mitchell warns not to go any higher unless it's recommended in your owner's manual.

"There's a lot of talk about B20 (20 per cent biodiesel), and at that level you could have an issue with seals or leaks, or injectors plugging, so it's best to find out what the manufacturer recommends.

"You hear about people running their VWs on french fry oil, but they're handymen and they're modifying their engines. It's way too thick to go through a normal diesel injection system, and they put heaters in the fuel. If it gets cold out, the stuff gets solid."

Several manufacturers currently offer diesels in cars and SUVs, including Volkswagen, Audi, BMW, Mercedes-Benz and Jeep. With many cleaner engines now meeting strict U.S. standards, it's probable that even more of these efficient models will be coming to North American showrooms in the future.

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