When I came across this fine shot of a 1940 Dodge delivering supplies to the fast-growing Howard Johnson’s restaurant chain, I was surprised to see the “DIESEL” badge on its hood. Hmm, diesels were quite uncommon yet in the US then, and those few that did exist were very large and heavy, built by Cummins or Waukesha or such, and not likely to fit under the Dodge’s rather modest sized hood.
I did a bit of searching, and to my surprise, this diesel engine was designed and built by Chrysler, starting in 1939. For one reason or another, it was only built through 1942, and never returned after the war. But it’s a fascinating historical footnote, especially to a company that pioneered diesel engines in light trucks three times afterwards until it found lasting success ; in 1962, using a Perkins, in 1978 using a Mitsubishi, and then of course finally in 1989, using the Cummins that it still sports today.
I found a quite comprehensive article on this engine at dieselworldmag.com. In the 1930s, diesel engines in trucks were making very slow headway in the US; less than a thousand were sold per year. In Europe, much higher fuel prices made them quite common, soon to be ubiquitous. Nevertheless, the improved economics were compelling, given that diesel (fuel oil) sold for $0.04 to $0.10 per gallon compared to $0.14 to $0.16 for gasoline. And of course the diesels used significantly less of it.
Chrysler was developing a new larger heavy duty flathead six inline six truck engine in the mid thirties, with 331 cubic inches. It decided to pursue a diesel version, with a totally different ohv head, of course, but with most of the block and its components shared. The key reason they could do so was because they licensed the Lanova Air-Chamber (a variation of a precombustion chamber), which significantly softened the typical pounding of early direct injection diesel engines. This was a key factor in their decision to proceed.
Here’s how the Lanova system worked:
The Lanova Power Cell was called the Twin Cyclone by Dodge. Here’s how it worked: The injector (upper) sprays across the combustion chamber, some directly into a small prechamber called an energy cell. The air in the cell is hotter than the rest of the combustion chamber, so about 40 percent of the fuel ignites in there and the flame front travels back out of the cell into the main chamber, creating turbulence and igniting the remaining 60 percent of the charge. Dodge claimed the initial combustion created 1,100 psi pressure in the cell but when the ignition occurred in the main chamber, it was only 700 psi overall. Combustion occurred slowly and gently, but surely. As a result, the Lanova system eased the stress on engine components during the power stroke so the engine structure could be made lighter duty… and lighter. It had the added benefit of making the engine smoother and quieter, an important part of transitioning the public to diesel. The Lanova diesels also delivered among the highest diesel fuel economy among the other systems out there at the time. It had some inherent power limitations but these did not count for much until later. As higher pressure injection systems evolved and were better able to atomize fuel, the Lanova Power Cell fell to the better-breathing, direct injected combustion engines with greater power density.
Precombustion chamber and Lanova Air-Cell diesels were attractive for these qualities, allowing lower pressure pumps (cheaper) and minimizing the intense loads on the pistons and bearings, as the combustion process was slowed down. Despite the claims above, they were inherently somewhat less efficient, which is why truck engines inevitably moved to only direct injection, and eventually cars too.
The T100 331 cubic inch diesel six had a 3.75″ bore and 5″ stroke, produced 100 hp @2600rpm and 226 ft.lbs. of torque at 1000 rpm. Somewhat interestingly, this was almost exactly the same as the T80 flathead gasoline version, rated at 100 hp @2800 rpm and 230 lb.ft. @800 rpm. Both engines got slight power boosts in 1941.
In 1938, Chrysler engineers compared the full-load fuel economy of the T80 gas and T84 diesel on a dynamometer at 2400, 1600 and 800 rpm. The results were telling. At 2400 rpm, the diesel used 6.6 gallons per hour while the gas engine used 10.7 gph. Even more dramatic, at full-load 800 rpm operation, the gasser stayed at about 10.7 gph while the diesel improved to 4.3 gph.
An over-the-road comparison of two otherwise identical 3-ton trucks showed the gas version getting 3.74 mpg and the diesel 5.23 mpg. That’s a solid 40% improvement, but then flathead engines intrinsically were a bit less efficient than ohv gas engines.
This shot shows the very low camshaft position that was a hallmark of flathead engines, and thus had to be shared.
The diesel required 24 volts for starting (four 6V batteries) but had a 6V system otherwise. This necessitated two generators; one 24-volt unit (the inner one driven by two belts) and one 6-volt (the piggyback, facing backwards), the belt for which also drove the vacuum pump.
Chrysler also made marine and military versions. but total numbers were quite low. Total diesel truck production from 1939-1942 was 606 units, and perhaps a few thousand military, marine and industrial units. It’s not known just exactly why Chrysler discontinued the diesel after the war; presumably it was either the demand was too low and/or there were issues with them.
It’s also possible that the GM two-stroke diesels that GMC started offering in its trucks in 1939 had some impact, as the their compact size and greater power output put the Dodge diesel at a disadvantage. Who knows? But at least we now know that Dodge was a pioneer in diesels going way back.