Why would a propane engine need to "warm up" to idle low?
Posted: Tue Aug 31, 2021 12:35 am
Was thinking about this while driving my 460 truck today. Most of my propane engines are governed and don't really "idle" in the same way the truck does against a closed throttle plate. They all start and run great from the moment you turn them over, but most are "idling" against a governor that maintains that idle speed.
The 460 idles beautifully once it has warmed up a bit but on a cold start has a bit of a lopey idle, and prefers a little bit of throttle opening to start reliably. Otherwise it will sometimes fire a couple times and fail to catch. But in a couple minutes it starts idling nicely, it definitely doesn't have to come up to thermostat temperature or anything.
We all know carbureted gasoline engines need to warm up a bit to get good atomization of the liquid fuel in the manifold, sometimes they even need a little choke to get going on a cold start even on a warm day.
But propane is delivered as vapour and once the air/fuel mix gets into the cylinder, shouldn't it burn just the same in a cold engine on a 30C day?
Doesn't seem to be an issue with the vaporizer needing coolant heat either to deliver enough vapour, since the engine will rev smoothly and the truck can be driven just fine.
Is this normal behaviour for a carbureted propane engine, or maybe I just need to change my spark plugs? However propane keeps them clean as a whistle so I don't see how anything would need to burn off the plugs on startup. Just wondering what the mechanism would be that requires the engine to warm up at all to run smooth.
The 460 idles beautifully once it has warmed up a bit but on a cold start has a bit of a lopey idle, and prefers a little bit of throttle opening to start reliably. Otherwise it will sometimes fire a couple times and fail to catch. But in a couple minutes it starts idling nicely, it definitely doesn't have to come up to thermostat temperature or anything.
We all know carbureted gasoline engines need to warm up a bit to get good atomization of the liquid fuel in the manifold, sometimes they even need a little choke to get going on a cold start even on a warm day.
But propane is delivered as vapour and once the air/fuel mix gets into the cylinder, shouldn't it burn just the same in a cold engine on a 30C day?
Doesn't seem to be an issue with the vaporizer needing coolant heat either to deliver enough vapour, since the engine will rev smoothly and the truck can be driven just fine.
Is this normal behaviour for a carbureted propane engine, or maybe I just need to change my spark plugs? However propane keeps them clean as a whistle so I don't see how anything would need to burn off the plugs on startup. Just wondering what the mechanism would be that requires the engine to warm up at all to run smooth.