Diesel vs gasoline, which engine to choose?

Posted by Krzysztof Lis on August 2, 2010

If you’re at the moment in your life when you’re looking for a new car, and believe you’re going to use it for a while, you should make a wise choice. If you don’t want an electric or hybrid vehicle, you don’t have much to choose from, but only gasoline (spark ignition) or diesel (compression ignition) engines. Which one should you buy?

There is no simple answer to that question. Those engines differ a lot in power/torque and efficiency/MPG, the fuels cost is also different. There are many additional questions you might ask to help you make a decision, e.g. do you want to spend more on the engine that will be more efficient and use cheaper fuel?

So let’s take a look at this question only from one point of view: the ability to use alternative fuels if standard fuels become very expensive or even unobtainable.

There are many different alternative car fuels, biodiesel, ethanol, methanol, compressed natural gas, hydrogen, liquefied petroleum gas (propane) and many more. Are those fuels suitable for both diesel and gasoline engines?

Well, many are suitable. For example, wood gas, CNG and LPG may be used in both diesel and spark ignition engines. If you don’t want to make serious adjustments to your engine, than the gasoline engine would be better, as the compression ignition engine needs some source of ignition — a small pilot dose of diesel fuel. If there’s no diesel, you won’t run your compression ignition on any alternative gaseous fuel without installing an entire ignition system: coil, spark plugs, controller, etc.

Think about all the alternative fuels you can make on your own, that is:

• vegetable oil / biodiesel,
• alcohol – ethanol,
• wood gas,
• biogas.

Only two of those fuels will work well in a standard diesel engine, the vegetable oil and biodiesel. The rest require some extra diesel (biodiesel) fuel for the pilot injection.

You should also take into account the amount of work and energy to produce your alternative fuel. The ethanol can be made of any sugar-containing biomass, from rotten fruits to garlic… The wood gas can be made of almost any hardwood, preferably dry one. Biogas can be produced from virtually any biomass, including human and animal waste. Yet the biodiesel can be made only from vegetable oils or animal fats, and it narrows your feedstock a lot.

So if you only think about producing your fuel in the uncertain future, choose spark ignition engine. You will be able to use a variety of alternative fuels, and not be limited to one.