How modern diesel engines are going green

Once used primarily in heavy-duty trucks, diesel is becoming more popular in passenger cars in Canada. Diesel engines are more efficient and get better fuel economy, and as a result, have longer range on a tank than comparable gasoline engines.

However, to meet strict North American emission standards, they require some extra exhaust treatment. Automakers use a Selective Catalytic Reduction (SCR) system. This includes the use of diesel exhaust fluid, or DEF, a pre-mixed solution of urea mixed with water, and sold under brand names such as AdBlue.

“By the nature of their combustion process, diesel engines put out different emissions than gasoline engines,” says Thomas Tetzlaff, public relations manager for Volkswagen Canada. “Injecting very minute quantities of urea cleans up the nitrates in the exhaust and allows us to reach emissions levels that were previously impossible in a diesel car. All our diesels are certified in all U.S. states, including California, which has the strictest laws on the planet.”

Diesel exhaust contains oxides of nitrogen, or NOx, a compound that contributes to smog. When small quantities of DEF are injected into the exhaust after it leaves the engine, it produces a chemical reaction that converts the NOx into nitrogen and water vapour, both of which are harmless.

The DEF isn’t added to the fuel tank, and it doesn’t travel into the engine. Instead, it’s added to a special reservoir, with the filler neck located beside the fuel filler, in the trunk, or under the hood, depending on the vehicle and the manufacturer. It’s automatically dispensed into the exhaust system as needed.

Although it’s easy for drivers to add their own fluid, manufacturers size the reservoir so it will generally need filling at the same time the car is due for its scheduled maintenance, so the dealer can top it up at that time. “We have a large-capacity tank located in one of the fenders,” Tetzlaff says. “It’s filled up mostly once a year, and it’s no more difficult than adding windshield washer fluid, and not a lot more expensive.”

When the reservoir starts getting low, the vehicle will warn the driver several thousand kilometres in advance, and continue with regular warnings as the fluid level drops.

If the reservoir runs dry, the car will continue to run, but once it’s shut off, it won’t start again until the DEF is replenished. The fluid can be purchased at dealerships, auto parts stores, and many gas stations.

Other changes

  • All diesel sold in Canada must be ultra-low-sulphur, which doesn’t have the “rotten egg” smell associated with diesel used in the past.

  • Diesel engines use compression heat to ignite the fuel, and don’t have spark plugs.

  • Unlike older models, modern diesel engines start right away, without waiting for the glow plug to warm up.

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