LPG mixture variation with temperature.

[Circlotron]

Been doing a bit of thinking about LPG setups with and without a cold air intake. It seems to me that as the engine temperaure goes up, naturally so does the water temperature and consequently so does the temperature of the gas coming out of the water-heated gas converter. If the engine air intake is sucking hot under-bonnet air then this air comes through the radiator and so it's temp more or less tracks the temperature of the gas coming out of the converter. So far so good.

Now consider the situation if you have a cold air intake. When the engine is cold the gas/air mixture might be just right but as the engine water heats up the gas coming out of the converter heats up and gets less dense but the cold outside air it gets mixed with with does not. Therefore the mixture goes gradually leaner the hotter the engine gets.

That means for example that you could set the idle mixture just right when cold but it just wont idle right when hot, or vice versa, good hot idle but bad cold idle because it is too rich.

Trying to think of some way to get around this. If your car has closed loop mixture control on gas then lucky for you, but even so, it probably runs open loop at idle so would still have the same problem. My best thought so far is to get some kind of very small trans cooler thingy with the s-shaped pipe and cooling fins and put it inside the airbox and run the gas through the pipe before it goes to the throttle body / mixer. That way the gas is made to equal the temperature of the air going through the cooling fins, and it tracks that temperature as it goes up and down so the air/fuel ratio should stay more constant. Any comments?

 

[CAPRILICIOUS WL]

In not that familiar with how the gas systems work However this sounds really smart.

 

[lease1]

Just go a liquid injected system

 

[Circlotron]

Just go a liquid injected system

Good solution but that would be about three time the worth of my car. I'll just go check with the missus and get back to you. :axe:

 

[Warranty Void]

most mixer systems run an input off the oxygen sensor so the mix is adjusted continually.

 

[strgas]

all good in theory as this happens on petrol to as fuel sits in the fuel rail to becomes warm due to heat soak more so on engines without a return line to the tank , as to the manifold heating as well adding to intake temp , the LPG convertor requires hot water to keep it from freezing while the gas goes from liquid to vapour , under hard accel the gas flow can increase inside the convertor and sometimes from poor water flow the convertor can start to freeze internally before the outside does causing the mixtures to run rich or lean depending on the affects of the flow , as most system fitted have a feebback setup or should have it will adjust mixtures as to the output of the O2 sensor , a colder air fuel mixturer will always run better as it able to hold more fuel in the air fuel mixture.