Continental's CMD-350; a 350HP multifuel engine

[davidb56]

Interesting. I thought perhaps it worked like the old International/McCormic tractors that started on gas and swapped over to diesel. They simply used an extra valve that allowed the gas side of things to work by increasing the combustion chamber volume (and hid the spark plug away from the cylinder). Then switched closed to allow the cylinder to achieve the higher compression needed of the diesel operation.

The varied oil pressure from the crank would allow it to operate more dynamically though. But I bet this setup lends to interesting failures.

I had a TD6 that worked that way. you could actually run it on gas, with less power for a while, but the gas tank only held about a gallon. I would forget to switch over sometimes. after it was warmed up, it would start on high compression with the diesel. that system would seem to be better than a variable piston compression. Spark plugs were designed to take the diesel fuel and compression abuse too. I fact, I had a Formal model H that I accidentally (I smoked pot back then) dumped 5 gallons of diesel in with about 2 gallons of gas in the tank, and cut the whole field for a few hours with no issues, other than a funny exhaust smell.

 

[rustystud]

My neighbor has a McCormick-Deering Farmall tractor that is set up that way. It’s pretty cool.

I had three 1940's IHC TD6 dozers that also started that way. My TD14 out back also started that way. Now it's a yard ornament since the differential broke.

 

[JasonS]

If you do a "google scholar" search, you can limit results to journal publications. A search for "continental aviation variable compression ratio" yields two interesting papers:

"A variable compression ratio engine development" by W. A. Wallace of Continental and F. B. Lux of the Army Tank Automotive Center; published in 1963 at the National Powerplant and Transportation Meeting. I can view but can't download the paper. However, I was able to attach two cutaway views of the piston.


"Recent Developments in Variable Compression Ratio Engines"; 660344
In an effort to produce military tank engines with more power per cubic foot of bulk and more power per pound of weight, Continental Aviation and Engineering Corp. has applied the Variable Compression Ratio (VCR) piston to an already developed, aircooled diesel engine. In this engine design, compression ratio is automatically varied within the piston by the use of hydraulic circuitry employing a control valve operating in response to changes in peak combustion pressure. To accomplish the dual objectives of smaller volume and lighter weight, Continental is developing, under U.S. Army sponsorship, an engine that is currently capable of producing 1.3 gross horsepower per cubic inch of piston displacement. Weight, including all engine and transmission cooling equipment, is 2.3 lb/gross horsepower. This paper presents the developmental background and some interesting technical details of this project.

 

[rustystud]

If you do a "google scholar" search, you can limit results to journal publications. A search for "continental aviation variable compression ratio" yields two interesting papers:

"A variable compression ratio engine development" by W. A. Wallace of Continental and F. B. Lux of the Army Tank Automotive Center; published in 1963 at the National Powerplant and Transportation Meeting. I can view but can't download the paper. However, I was able to attach two cutaway views of the piston.


"Recent Developments in Variable Compression Ratio Engines"; 660344
In an effort to produce military tank engines with more power per cubic foot of bulk and more power per pound of weight, Continental Aviation and Engineering Corp. has applied the Variable Compression Ratio (VCR) piston to an already developed, aircooled diesel engine. In this engine design, compression ratio is automatically varied within the piston by the use of hydraulic circuitry employing a control valve operating in response to changes in peak combustion pressure. To accomplish the dual objectives of smaller volume and lighter weight, Continental is developing, under U.S. Army sponsorship, an engine that is currently capable of producing 1.3 gross horsepower per cubic inch of piston displacement. Weight, including all engine and transmission cooling equipment, is 2.3 lb/gross horsepower. This paper presents the developmental background and some interesting technical details of this project.

Thanks Jason. That is really quite cool ! So the piston itself was a "self contained" unit. Wonder if any of those pistons survived.

 

[V8srfun]

Static and dynamic compression are not always the same and in most cases are not the same. Almost all modern engines have hydraulic phasers on the cam gear to change cam timing (some engines more than 60 degrees of range). That would be the easiest way to change dynamic compression by effecting your valve closing time to allow some of the compression stroke to happen while the valves are not yet closed.

Volvo had a production gas engine with variable compression where it actively changed the combustion chamber volume with a really complicated cylinder head design that I don’t believe was all that reliable.

I don believe it has been done before but it would be possible to use both the Honda vtec type system or a Jake brake overhead type system to modify valve timing to change your static compression.

Nissan infinity is currently using a pivot on the crank shaft to alter compression ratio of one of their 4 cylinder turbo gas engines.