News
Comment

Forget electrics and hybrids: take a fresh look at diesels

They're more efficient, go further, and run on cheaper fuel

  • Rudolf Diesel

Rudolf Diesel jumped or was pushed off a steamer heading from Antwerp Belgium to Harwich England on Sept. 29, 1913.

He was either destitute and depressed, or he was murdered by those who stood to lose from the wider-spread adoption of his “compression-ignition” engine.

We’ll never know.

In any event, Diesel left us a better form of engine.

Diesel’s invention was more efficient and produced more torque than contemporary steam or gasoline engines.

This soon made it the choice for stationary engines, and for larger vehicles such as trains, ships and trucks, where the greater weight of its more robust construction was of less concern than it was in smaller vehicles.

As manufacturing techniques and materials improved, the weight of the engines was reduced, and they became more popular for passenger cars.

How do diesel engines work?

Any so-called “four-stroke” reciprocating piston engine works on similar principles.

The four strokes:

1. Intake. An air-fuel mixture is introduced into the cylinder.

2. Compression. The mixture is compressed by a piston moving upwards inside the cylinder.

3. Combustion. The air-fuel mixture is ignited, and the gases that result force the piston back down the cylinder, creating torque.

4. Exhaust. The piston moves back up the cylinder, and those burnt gases are expelled from the engine.

What happens next? The other end of the piston is attached to a connecting rod, which is fitted to a crankshaft.

Think of riding a bicycle: your lower leg is the piston and connecting rod; the pedal attached to the crank turns the shaft that in turn drives the chain.

The main difference between gasoline and diesel engines is that, in a diesel, the spark is not applied to the fuel-air mixture to initiate combustion. Instead, the mixture is compressed to such a degree that the higher temperatures created cause it to ignite spontaneously.

More of the force created by the expanding product of the combustion is converted to torque, and less is lost to heat.

A diesel is about 20-per-cent more efficient than a gasoline engine.

The overriding characteristic of diesel engines is strong torque at lower revs. They also don’t need high revs to generate maximum performance.

As any fuel will only burn properly if it is mixed in correct proportion to air, and you can squirt any amount of fuel you want into a cylinder with high-pressure fuel-injection, the output of any internal combustion engine is limited by how much air you can stuff into the cylinders, to maintain the correct proportion.

Pressurizing the intake air, either by a compressor driven from the engine (called a “super-charger”) or driven by exhaust gasses (a “turbo-supercharger,” a term generally shortened to “turbo-charger”) is the answer.

Virtually all diesel engines use turbo-chargers, which are also now becoming more popular with gasoline engines, because you can get more output from less fuel.

Engines running on a diesel cycle can also use vegetable-based oils. (They smell like burned French fries.) So-called “bio-diesel,” where all or some component of the fuel is vegetable-derived, is a potential environmental advantage.

Rudolf Diesel

If diesels are this good, why aren’t all car engines diesels?

Due to the more robust construction needed to withstand the higher internal pressures involved, diesel engines are heavier and more expensive to build. The injection systems needed to introduce the fuel are more complex and expensive, too.

And they tend to be slower in acceleration off the line. But, as a friend of mine used to say, “If your car goes 0 to 100 km/h three seconds quicker than mine, then you’ll get to Montreal three seconds ahead of me. But if you have to stop to refuel and I don’t, then I beat you.”

And the meaty torque in the mid-rev ranges makes diesels very pleasant on the highway.

In earlier times, diesels were noisy, due largely to the higher pressures involved in the combustion process. Again, at highway speeds, I find this creates a nice relaxing “thrum,” although I admit it may be an acquired taste.

Newer engines are still rattly at idle, especially on a cold start. But once warmed up, they are much quieter than they were before.

When they are not properly tuned, diesel engines can emit huge clouds of black smoke: unburned carbon. Pretty rare on passenger cars these days, although you still see some trucks doing this.

My two VeeDub diesels are now three generations old, and, despite their elevated mileages, still emit no visible smoke whatsoever, and easily pass the Drive Clean test.

Diesels are more environmentally friendly when it comes to emissions of carbon dioxide. Because diesel engines are more efficient overall than gasoline engines, they use about 20-per-cent less fuel, and produce roughly 20-per-cent less CO2.

Diesels do have one emissions issue: Air is about 78-per-cent nitrogen and, when combustion takes place inside the cylinder, the higher temperature in a diesel engine creates more oxides of nitrogen as a by-product.

Collectively, these are referred to as NOx. These are major contributors to the formation of smog, and are the most difficult of diesel emissions to control.

The solution is a mixture of 32.5-per-cent urea in water, injected into the exhaust stream.

Urea is a chemical compound containing hydrogen, nitrogen and oxygen. It is most commonly used as a fertilizer for its nitrogen content. It converts the NOx into pure nitrogen and carbon dioxide, which are natural components of our atmosphere.

The solution must be metered ever so precisely into the exhaust system. Typically, the tank holds enough urea for about 15,000 km of driving, and is refilled as part of routine maintenance.

One concern about diesels remains: The fuel stinks. It isn’t the urea; it’s the sulphur in the diesel.

Today’s ultra-low sulphur fuels have reduced this problem significantly, but my VeeDubs both have boxes of latex gloves, which I use for re-fuelling purposes. You also have to be careful not to step in any puddles near the diesel pump in your Gucci loafers.

But the main reason we don’t have more diesels in Canada is Americans don’t want them, and our small auto market doesn’t justify the investment by car manufacturers.

Why don’t Americans like diesels?

Consumers in the U.S. had an unfortunate experience with General Motors diesels, under the Oldsmobile brand. In an attempt to mitigate the impact of the OPEC oil crisis of the 1970s, the carmaker converted gasoline engines to diesels. The engines were very sensitive to improper maintenance. Americans generally were not used to maintaining their engines, and they often blew up.

Also, gasoline in the U.S. is effectively free, compared to what we and most of the rest of the world pays.

So there is little incentive for Americans to buy more fuel-efficient vehicles when they cost more, as diesels do.

Lack of demand means lack of supply. So diesel fuel is not as widely available in the U.S. as it is here. There, you may have to go to a truck stop. Not that handy.

Diesel fuel also tends to be more expensive than gasoline in the U.S.

The higher initial cost of diesel engines, exacerbated by expensive urea-injection systems, means you do have to drive a lot of klicks to make the pay-back work.

But this makes them ideal for commuters who cover long distances.

That’s why the Volkswagen TDI Diesel Golf or Jetta is the official car for commuters who make their way into Toronto from such places as Barrie. (I swear, a third of the cars on Hwy. 400 are TDIs.)

Do diesels have a future? Beyond a doubt!

It would help if the U.S. government would stop messing about with higher fuel-economy mandates, and simply raise the price of fuel.

That would improve the pay-back ratio for alternate fuels, and the market would sort the economics out in a few months.

On a level playing field, I think diesels would swamp hybrids or electrics. Even with massive subsidies for electric and hybrid vehicles, Americans still buy more diesel automobiles than the other two technologies combined.

And new developments are on the horizon.

With its SkyActiv Diesel, coming later this year in the Mazda6, Mazda has figured out how to ignite diesel fuel at a lower-than-usual compression ratio (14.7 to 1, versus the more common 16:1 to 20:1).

The lower the internal pressure, the lower the temperature of combustion, and the less NOx is likely to form. Mazda claims its engine can meet up-coming U.S. emissions standards without urea-injection, which will knock maybe $1,000 off its cost.

If this engine works, if Chevy’s Cruze Diesel sells well, if Volkswagen ever gets around to building enough TDI engines to meet world-wide demand, there just may be a diesel engine in your future.

Lucky you! Rudolf Diesel would be a happy man.

Rudolf Diesel

wheels@thestar.ca

Follow Wheels.ca on
Facebook
Instagram #wheelsca
Twitter

 

Show Comments