Measurement & Instrumentation


Clean Diesel: Marketing Nonsense or Viable Alternative?

by Pramod Dibble 09 Dec 2014
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When confronted with marketing of any kind, I find myself becoming increasingly skeptical. The incentive for misrepresenting the truth (i.e. lying) is massive, and repercussions seemingly nonexistent. This is particularly true in scenarios where a product or service has a very pervasive reputation and the provider of that product or service begins an antonym-based branding campaign, i.e. “clean” coal, “child-safe” cyanide, “non-proliferatable” plutonium (I made some of those up). But this skepticism does not necessarily indicate that the marketing word is inaccurate. After all, scientific breakthroughs can eliminate or alleviate the problems a product or service once had, and it seems unjust of me to simply discount a new discovery based on past biases.

                A slew of car manufacturers including Volvo, Audi, BMW, Chevrolet, and Jeep have begun introducing “clean” diesel cars. And while the perception of diesel cars is smog-generating, noisy, and very “meh” cost-to-value ratio, these new models are significantly different from the old ones that a new analysis seems necessary. Such as it is, this analysis follows.

                Diesel contains roughly 13-14% more carbon dioxide than an equivalent quantity of gasoline; it follows logically that the diesel engine must be a minimum of 13-14% more efficient than the gasoline engine in order to be less environmentally harmful. But good news, diesel engines are typically 20-30% more efficient than gasoline engines as a result of the fuel injection process; high pressure/temperature air injection (diesel) as opposed to spark plug ignition (gasoline).While good for efficiency, this process results in a unique “knocking” sound which some consumers find unpleasant; the characteristic noisiness of diesel engines. So far, the diesel engine is 6-13% more fuel efficient than the gasoline engine: diesel 1, gas 0. Unfortunately, diesel currently cost 20-25% more than gasoline, so you’ll still be spending more at the pump than your gas-using friends. Diesel 1, gas 1.

Diesel is a natural lubricant, thereby potentially extending the longevity of the engine itself, though this rarely translates into consumer savings, as the components are more expensive, resulting in fewer but costlier maintenance events. Tax incentives for “clean diesel” vehicles have expired, and most consumers pay far more for a diesel vehicle than they would for one running gasoline, predominantly a consequence of no manufacturer currently making a low-cost option. This may change is if the technologies catch on and become commoditized. I’m calling this a wash: diesel 1, gas 1.

Biodiesel, the truly “clean diesel” tends to comprise less than 5% of any diesel fuel; any more than that and the natural lubrication diesel provides is reversed and engines need prohibitively high maintenance and care. “Clean” diesel (aka ultra-low sulfur diesel) contains 97% less sulfur than traditional diesel, and 40% less particulant; which is an awesome development. However, smog-causing nitrus-oxide (NOx) levels are unchanged. Again, a wash.

In conclusion, “clean” diesel is very clean when compared to conventional diesel engines, and more or less comparable to gasoline ones if we take both cost-to-own and environmental impact into consideration. However, when compared to other emerging car-fuel technologies like all-electric, hydrogen, and even hybrid electric-gasoline, “clean” diesel is a distant last (CO2 emissions from “clean diesel” vehicles are about 50% higher than a comparable hybrid-electric vehicle). The concept of a hybrid diesel-electric car is an intriguing one, and I would like to see more work in that area. But if your priority is environmental consciousness, and you’re in the market for a luxury car, you can do much better than “clean” diesel.

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