IS THERE A DIESEL IN YOUR FUTURE?
Recently, the buzz in engines has been around diesels, especially in Europe. Remember when we talked about the infrastructure for alcohol fuel? Well, the problem is much easier with diesel because Jet A is already commonly available and, in fact, is the only aviation fuel available in some parts of the world. Jet A is quite close to diesel fuel, and most diesels need only a new fuel pump to deal with the different lubricating properties of Jet A. Why are diesels such an appealing alternative? For starters, there has been a tremendous improvement in the performance of modern automotive turbocharged diesels. Technologies such as common rail injection, casting techniques and the introduction of low-sulfur diesel fuel have combined to make modern automotive diesels quiet, powerful, economical, and not nearly as heavy as those of a generation ago.

The turbocharged 135 horsepower, jet fuel operated, aircraft engine “CENTURION 1.7” (by Thielert Aircraft Engines GmbH) had already been certified in Europe to JAR-E for jet fuel and diesel when the validation to FAR 33 for the US-market was issued in October 2003. This engine is currently powering the 4-place Diamond DA40 Diamond Star (shown above) and the 4-place DA42 Twin Star, twin engine aircraft. Additionally, on October 28th, 2004, the 310 HP V8 jet fuel engine CENTURION 4.0 was certified in Europe.

At the small end of the scale, there are several automotive diesels currently being tested that may work nicely for 1-2 seat aircraft. An example shown below is the Opel turbo-diesel being converted for use on the Dutch RangeR kitplane.

  THE BOTTOM LINE?
We will see more and more aircraft being fitted with automotive-based diesels. As the price of Avgas rises in the US, the level of interest there will grow with time.

HYBRIDS
If they are so hot in cars, what about light aircraft? Hybrids, or electric/internal combustion combination powerplants, are currently the darling of the automotive scene in the US. From an aviation point of view, the Achilles heel of hybrids is the weight of the battery pack and electric

The Thielert engine started life powering the humble Mercedes-Benz, A-class automobile.

The most successful aviation diesel, the Thielert Centurion (pictured above), is an aviation adaptation of a Mercedes-Benz automotive engine. The automotive parentage is, I think, a key to the near term success of new technology aviation diesels. Thielert has proven that it is possible to take mass-market engine technology and adapt it to general aviation requirements. The French SMA diesel engine, a design not derived from an automotive base, has had great difficulty in getting traction in the market. The manufacturer has recently gone into a form of bankruptcy, so it remains to be seen if they survive or not. The fact is that general aviation is a tiny market compared to the automotive world. If we want to reap the benefit of the progress made there, it will probably be necessary to adapt automotive technology and components instead of designing a bespoke aviation engine. Conventional wisdom used to have it that auto engines would not work, as they are designed to loaf along at, say, 25% power, while aviation motors are loaded up at 75% power for most of their life. The success of the Thielert shows that properly done, this is no longer necessarily true. The low fuel burn of the Thielert engine when compared to the equivalent Lycoming is really impressive. The performance of the new Diamond DA-42 Twin Star has made people sit up and pay attention to the potential of aviation diesels.