The first truck I ever drove (in Vietnam in 1968) was an Army two-and-a-half-ton cargo vehicle powered by a multifuel diesel engine. It sounded more like a car engine than a truck diesel and would burn anything but high-octane gasoline. Even more interesting was that even though the engine used compression ignition, it didn’t require fuel with a high cetane rating.

In 1973, I interviewed Max Fiedler, a local engineer who wanted to produce a small diesel engine he said was very light, would run more quietly than a standard diesel engine and would do so without smoke. Fiedler’s engine defied all the standard diesel rules about how the injection system should work. He used very low injection pressures – 1,200 psi or less.

Today’s diesels use 26,000 to 30,000 psi. Normal diesels use the timing of the fuel injection to control the timing of the combustion. I thought the engine might smoke or knock due to poor atomization, but a demonstration dispelled that concern. The little machine started and ran smoothly with no diesel knock or smoke – white or black.

Fiedler bolstered my confidence in him by presenting me with a copy of his 1939 paper, published by Philadelphia’s respected Franklin Institute. I have since read extensively about advanced diesel combustion systems. I discovered, for example, that Sigfried Meurer, the German engineer who masterminded the engine used in my Army truck, agreed with Fiedler on most of the basic points of his theory.

The theory is quite simple: If you can thoroughly mix diesel fuel with air, you will prevent combustion knock and diesel smoke. Reducing audible knock also reduces nitrogen oxide emissions.

Few engineers today discuss Fiedler or Meurer, but there is a rapidly growing body of research based on their work. It’s called HCCI, or “homogeneous charge, compression ignition,” sometimes called “pre-mix” diesel combustion.

Beginning in the early 1990s, Japanese engineers picked up the idea – or perhaps even reinvented it. In 1999, a group of engineers from Nissan Motor Co, Ltd. and the Musashi Institute of Technology published a paper on the MK engine – a small, direct-injection, turbocharged car engine. The engine uses cooled EGR – as much as 32 percent of the volume of gases taken in through the valves is recycled exhaust – and its injection system has some basic similarities to Fiedler’s.