Lubrication and Cooling

[SteamFreak]

I am looking to refit a diesel engine for uniflow steam. Steam will be at 385-400 degrees F and rpm will likely be in the 500 range at full power (estimate). My inquiry surrounds what oil I can use for lubrication. It can't vaporize at 400-450 degrees F. It cannot require heating to pump and if its possible to use the original oil pump, thats good too.

The Second part is cooling. With 390 degree F steam, I'm operating with a working substance far below the 1300-1500 F compressed air at the pre-ignition and even farther below that of the combustion cycle. Can I get away with just letting the oil cool the engine (along with, perhaps, a fan to drive exterior air over the engine?) and do away with the circulating jacket water? Or can I have a cooling tank and sea water heatexchanger to induce natural circulation? Or, perhaps, can I simply cycle my feed water for the boiler through the jacket before it is forced into the boiler, using the water pump to maintain a constant flow? If I circulate the feed water through the jacket, should I pre-heat it to avoid some sort of thermal shock?

Alot of questions and please don't hesitate to give detailed answers and reasoning... I've spent 3 years sailing on ships and 2 years running a small steam launch.

[fredrosse]

This has been done many times. The engine will not need cooling, in fact you want to insulate the cylinders and head from any cooling effect.

Finding oils suitable for your service depends on several engine parameters. If you can keep your crankcase and above 220F then no water will accumulate, and many IC engines routinely operate with oil temperatures well above 220F. The problem of oil finding its way into the boiler (for condensing systems) is usually a greater concern.

I had an industrial engine conversion to Uniflow Steam running on 150 PSI saturated steam to generate power at my house. This engine ran with pure mineral oil to allow separation of the water that could find its way into the oil sump. The engine used poppet valves, and no oil was injected into the steam. There is an ASME paper on this system.

Look on the internet at the "Whitecliffs" project. They used a three cylinder diesel engine conversion to run a 25,000 watt generator at 1500 RPM on Solar Generated Steam.

[SteamFreak]

I wasn't so much worried about water accumliation in the crank as I was introduction of oil to the feed water. Did the mineral oil vaporize into the feed system?

[fredrosse]

Pure mineral oil will not form an emulsion with the feedwater, therefore it can be separated from the feedwater by ordinary skimming and a disposable paper (or cloth) filter. When the filter becomes saturated with oil, replace it, and throw the wet oily filter into the furnace. Look at how oil removal was done on the Liberty Ships of WWII. The old "towel and excelsior" filters generally removed enough of the oil that the boiler did not suffer. I understand that some of the new poly plastics have an even greater affinity to attract and hold oil.

[SteamFreak]

Ah... I had not known that about mineral oil. We use oil-absorbant pads we call diapers to mop up oil and if the mineral oil does not emulsify, then skimming seems precisely the thing to do. Just as side query though, how well does mineral oil vaporize? Mind you, I'd not like to have to carry significant quantities of mineral oil because it boils off when in contact with the steam.