I got a John Deere 6068T diesel that I'm building a new CHP unit with, that will be big enough to heat both my shop and the house.
These are from Deere’s industrial lineup of G-drive and marine engines. They are HPCR with electronic unit injectors. Rated for 50,000 hrs to overhaul on irrigation or generator duty. It is 180hp @ 1,800 rpm and holds 45 liters (11.9 gallons) of oil, making it possible to run 500 hrs between oil changes. Used drain oil from the engine can go into the fuel tank, diluted with fuel and be burned. It is suitable for driving a 125KW split-phase generator and considerably more fuel efficient than our Caterpillar DE50. The 6068T is a Tier II engine, doesn't require use of DEF, 106mm bore x 127mm stroke giving it 6.8L (415 cubic inches) of displacement. It is 17:1 compression ratio, turbocharged and designed for intercooling, so heat can be extracted from the intercooler as well as the cooling system and exhaust.
The cooling loop for the engine (heating loop for the house and shop) will go thru the intercooler, then thru the engine's cooling system, then thru the exhaust cooler. Exhaust temperature @ rated load is 1,000F. The cooling system will be high pressure (25 psi) so the final stage in the loop will be heated to 280F 50/50 glycol-water that goes to the heat exchangers. We need enough radiant heat from the engine to heat the generator room and fuel system when it's below -20F outside so the engine block and exhaust manifold under the turbocharger won't be insulated. The engine weighs 1,820 lbs wet, so it has decent thermal mass as well, for continued heating of the generator room/fuel system when it is shut down without having have to use auxiliary heating to heat the room in sub-zero temps.
I chose this engine because it is near the pinnacle of current technology in diesel engines for thermal efficiency. It has 42% brake thermal efficiency at full load (fuel energy converted to mechanical power), with 28% wasted in exhaust gas, 4% going to pumping losses in a four-stoke cycle engine, 26% of fuel energy dissipating to cooling media as heat rejections to the ambient, including 3% going to mechanical losses as heat. It can be run at partial loads to adjust electrical and heating output as needed, just as efficiently as it runs at full rated load. Modern electronically controlled diesels are a total different world from the mechanical injection diesels of yesteryear, as the electronically controlled units can adjust both fuel rate and timing on-the-fly to optimize cylinder and turbocharger boost pressure and minimize emissions at partial loads. Unlike Otto-cycle engines, diesels run at peak volumetric efficiency because they are un-throttled, so they are an inherent lean-burn design with air-fuel ratios as high as 200:1 at very light loads in modern electronically controlled engines. The best an old Lister thumper could manage was ~40:1 air-fuel ratio at idle and around 15:1 at full load - not much better than a Otto-cycle engine. These new diesels run so clean they don't even leave any black soot in the exhaust pipes anymore. This particular engine can't qualify for on-road use because of NOx emissions, as it doesn't use SCR and runs extremely high combustion temperatures because it doesn't have cooled-EGR. But for a CHP unit it is perfect.
Total cost of the project I estimate at around $105,000 - the engine itself was a $27,000 component. Unfortunately, none of our existing plumbing or heat exchangers will work because they are a low pressure system. So we have to start over from scratch on the heating/cooling loops. It won't be running for this winter, but hope to have it completed for initial testing by next fall, and in full operation for next winter.
Edit: another plus with this engine is that is classified as a heavy duty industrial engine. It is used in John Deere ag and constuction equipment as well as G-drive and marine applications. It has replaceable wet cylinder liners, four valves/cylinder, the inline-six configuration has perfect primary and secondary balance without use of balance shafts, and the water pump is gear-driven instead of belt. It is very similar in design to the big block Cat (3406E/C15), which I think John Deere copied it from. But like the big block Cats, which became the first 2 million miles to overhaul engine in heavy duty trucks, this engine is designed to last with minimal maintenance.
