HiPerTEC,
It wasn't the OPOC, but it was for TACOM and it was called the TRC Engine (Turbo Rotary Compound). It was an opposed piston, uniflow 2-cycle reciprocator coupled with a (Wankle type) compressor/expander.
To make it capable of withstanding the high peak cycle pressures (275 bar)it was intended to operate at, each piston had two con rods. And the single cylinder test rig had a total of four gear-synchronized, counter rotating cranks. In theory, opposed piston engines have excellent dynamic balance, but in order to improve scavenge efficiency, we usually ran the intake and exhaust pistons up to 10 degrees out of phase. To make matters worse, the combined reciprocating mass (30 lbs?) of each piston/conrod assembly was very high, so the the unbalance forces (shaking) due to the intake/exhaust pistons being out of phase was quite high.
The test rig was a 124 cu.in. single cylinder unit, and each of the four cranks had it's own 90 lb. flywheel. But even with all of that flywheel mass it still shook the entire building when it ran.
The thing that always scared me the most was starting it up. It had a very low compression ratio (12:1, the rest of the compression/expansion work was to be performed by the Wankle unit) but utilized very high levels of manifold pressure (8 bar), so it was a bear to start. The test rig had no starter, so we would motor it up to speed using the DC dyno, set the externally supplied intake air pressure and temperature to spec, and then begin to turn up the rail pressure control on the 25 ksi fuel injection system. All of a sudden the thing would light off with a deafening roar and everybody in the control room would jump, even though they had been through the start-up drill dozens of times before.
Now that I look back on that program, I'm amazed we never had a serious accident in the test cell. The high pressure common rail fuel system was state of the art for 1993, but it was still a development unit. Being a test rig, we were constantly tearing the engine down for inspection and when we would reinstall the common rail fuel system, it would usually take 4 or 5 attempts to get all of the 25ksi fuel fittings to seal properly. The fuel pump was engine driven, so we would have to motor up the engine to pressure check the fuel system. I don't know if you've ever seen a leak from a 25ksi fuel system, but one second it's fine and the next instant there's a huge cloud of super-atomized fuel surrounding the engine inside the enclosed test cell. Perfect conditions for a huge explosion. Luckily we never had an explosion. Maybe God takes pity on fools.
Sorry to ramble on, but it was a great program to be involved in and I worked with a lot of sharp guys from Detroit Diesel and Sandia Labs.
