The Diesel Dilemma

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Diesel-powered cars could be the ticket – as far as giving us very high-mileage cars (50-plus MPGs) with excellent power/performance and without the liabilities of hybrids – including the additional expense/complexity of having two powerplants (a gas engine and an electric motor) in the same vehicle – or the compromised economy/performance of hybrids at highway speeds.

But, as my week in the just-launched 2014 Chevy Cruze diesel made all-too-plain, the government is making it very hard to make a case for diesel-powered cars.

I’ll explain.

The Cruze I test drove (read the review here) comes with two features that many potential buyers may not like. Unfortunately, they are not optional. If you buy the car, you’re stuck with them – just like Claymores in the dashboard (air bags), always-on headlights (Daytime Running Lamps) and other such things force-fed to the American car buyer.

The first of these features is a particulate (soot) trap built into the exhaust system. It must be periodically “regenerated.” Very high heat (from driving the car) is used to burn off accumulated soot, thereby preventing it from pouring out of the tailpipe. This is the chief reason why modern diesel cars don’t smoke – unlike the diesel-powered infamies of the past. This is wonderful. Except for one thing. If you don’t drive the car long enough or fast enough (20-30 minutes continuously at speeds of 30 MPH or more) the “regeneration” cycle won’t work as designed. The accumulated soot isn’t burned off. Instead, it builds up inside the system. Which makes the system unhappy. And that makes the car’s computer – which controls everything – unhappy. In turn, you will soon be unhappy. Because the car’s computer will flash a “trouble code” (a dashboard warning light will appear) and it will then limit how fast the car can be driven – until you take it in to Mr. Goodwrench to get that Great GM Feeling.

If you do a lot of highway driving, you may never have this problem. But people who only use the car to commute, who do mostly stop-and-go driving, may be in for an unwelcome surprise. I wrote a column a few weeks ago (see here) about the DC ambulance that went kaput by the side of the road – with a dying patient inside – as a result of the vehicle’s computer getting pissy because the “regeneration” cycle never had a chance to do its thing – the ambulance being used infrequently and mostly driven for short distances at lower speeds. That was a Ford. Be advised the “regeneration” thing is by no means just a GM thing. It is becoming a universal thing – because it is the only thing that keeps particulate emissions in line with what the EPA demands. You can agree or not that curbing soot to nil is a good thing. The question is whether it’s smart to be so strict if the only way to do it is to make diesel-powered cars vulnerable to random unplanned pit stops. Because buyers aren’t going to like that. And once word gets out, they may not buy diesel-powered cars. Which kind of makes the whole exercise pointless. Unless the point of the exercise is to strangle diesel-powered cars in the crib, before they get a chance to win hearts and minds – and achieve widespread consumer acceptance.

The next diesel “feature” is potentially much more of a consumer turn-off: Urea injection.

You’ve no doubt heard about catalytic converters. All gas-powered cars have these devices. They catalytically (chemically) convert exhaust gasses from obnoxious and harmful to not-obnoxious and harmless – which is why the better part of any modern car’s exhaust stream (upwards of 95 percent) is composed of water vapor and carbon dioxide, both compounds having no ill effect on the quality of the air we breathe. Well, urea injection in diesel engines works on a similar principle. By spraying a shot of urea – basically, horse pee – into the hot exhaust stream, the exhaust gas is chemically changed to more benign compounds. But unlike the gas-engined car’s catalytic converter – which requires no periodic maintenance – a diesel-powered car’s urea injection system requires regular topping-off of the urea tank. In the Cruze, there’s a filler neck in the trunk. The tank holds about five gallons of the stuff – which is typical.

So, what’s the problem?

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