Thermodynamics of a supercharged car, powered by compressed petroleum gas.
January 17, 2011 7:09 PM Subscribe
Thermodynamics of a supercharged car, powered by compressed petroleum gas.
I dropped out of engineering before I had a keen grasp on thermodynamics, so I have a question for the hive. (I'll explain in layman's terms so those readers along for the ride can get a grip on things, along with those who have a chance of actually solving this problem!)
So, firstly a supercharger compresses the intake charge. This compression raises the temperature. As a result, an intercooler is usually employed to reduce the temperature of the intake charge.
Secondly, the LPG (liquefied petroleum gas, in the USA I think you guys use propane as the equivalent) is vaporised in a converter. This is like a refrigerator, so the converter will actually freeze if not for the hot fluid from the radiator being piped through it.
It would seem to me that a supercharged (or turbocharged) car powered by LPG is in the unique position of being able to cool the intake charge, not just with ambient temperature air, but with a refrigerator - the vaporising fuel. It could even be done with existing componentry. A "water-to-air" intercooler could be used, but rather than piping the water down to a front-mounted radiator, it could be piped through the gas converter instead.
So here is my question(s):
1. How much energy would the vaporising LPG "eat"?
2. How much energy needs to be removed from the intake charge (compressed to say, 10 PSI above atmosphere) to sufficiently cool it?
Basically, would the vaporising LPG have a substantial enough effect on the intake temps to make the design worthwhile, and would the compressed intake charge provide enough energy to ensure the converter wouldn't freeze over? Feel free to ask for data estimates if required.
Thanks for your help :)
I dropped out of engineering before I had a keen grasp on thermodynamics, so I have a question for the hive. (I'll explain in layman's terms so those readers along for the ride can get a grip on things, along with those who have a chance of actually solving this problem!)
So, firstly a supercharger compresses the intake charge. This compression raises the temperature. As a result, an intercooler is usually employed to reduce the temperature of the intake charge.
Secondly, the LPG (liquefied petroleum gas, in the USA I think you guys use propane as the equivalent) is vaporised in a converter. This is like a refrigerator, so the converter will actually freeze if not for the hot fluid from the radiator being piped through it.
It would seem to me that a supercharged (or turbocharged) car powered by LPG is in the unique position of being able to cool the intake charge, not just with ambient temperature air, but with a refrigerator - the vaporising fuel. It could even be done with existing componentry. A "water-to-air" intercooler could be used, but rather than piping the water down to a front-mounted radiator, it could be piped through the gas converter instead.
So here is my question(s):
1. How much energy would the vaporising LPG "eat"?
2. How much energy needs to be removed from the intake charge (compressed to say, 10 PSI above atmosphere) to sufficiently cool it?
Basically, would the vaporising LPG have a substantial enough effect on the intake temps to make the design worthwhile, and would the compressed intake charge provide enough energy to ensure the converter wouldn't freeze over? Feel free to ask for data estimates if required.
Thanks for your help :)
I think the system you're describing with a converter is for vapour injection, but the state of the art for LPG is liquid phase injection.
posted by onya at 7:56 PM on January 17, 2011
posted by onya at 7:56 PM on January 17, 2011
LPG is not widely available as an automotive fuel.
LPG is quite widely available in Australia due to favourable tax status making it about half the price of petrol, it's commonly used by taxis.
posted by onya at 8:02 PM on January 17, 2011 [1 favorite]
LPG is quite widely available in Australia due to favourable tax status making it about half the price of petrol, it's commonly used by taxis.
posted by onya at 8:02 PM on January 17, 2011 [1 favorite]
Ok, not specific data related, but more overall:
Basically, would the vaporising LPG have a substantial enough effect on the intake temps to make the design worthwhile, and would the compressed intake charge provide enough energy to ensure the converter wouldn't freeze over
Part of the issue (in considering the value of the system) is that you're not considering the energy involved to compress the LPG. Not adding up the full system energy requirements, as it were. The intercooler is relatively established in terms of power consumption (and the merits and issues compared to a turbocharger are well established) but the main advantage of both systems over the LPG process is that the action of driving along takes away the heat disadvantage of the compression process - basically, returning the compressed charge back to close to ambient temperature is 'free' other than a slight additional drag for the extra radiator. The energy to cool the LPG comes directly from the engine - losses are inherent in that process that won't be recovered and no free energy is available to help with that.
So, I guess what I am getting at is that LPG is not an 'extra power' system. It has major additional penalties in equipment (the tank and converter and the packaging difficulties and compromises inherent in that system) and doesn't really give you a power advantage - most of the technology efforts in LPG development has been in getting them to compete in terms of power to efficiency figures. Intercoolers are a definite power add in terms of net energy usage, LPG is not at present. Yes, on paper it looks like it is, but the extra weight and energy requirements just allow you to use an alternative fuel rather than gain power.
posted by Brockles at 8:12 PM on January 17, 2011
Basically, would the vaporising LPG have a substantial enough effect on the intake temps to make the design worthwhile, and would the compressed intake charge provide enough energy to ensure the converter wouldn't freeze over
Part of the issue (in considering the value of the system) is that you're not considering the energy involved to compress the LPG. Not adding up the full system energy requirements, as it were. The intercooler is relatively established in terms of power consumption (and the merits and issues compared to a turbocharger are well established) but the main advantage of both systems over the LPG process is that the action of driving along takes away the heat disadvantage of the compression process - basically, returning the compressed charge back to close to ambient temperature is 'free' other than a slight additional drag for the extra radiator. The energy to cool the LPG comes directly from the engine - losses are inherent in that process that won't be recovered and no free energy is available to help with that.
So, I guess what I am getting at is that LPG is not an 'extra power' system. It has major additional penalties in equipment (the tank and converter and the packaging difficulties and compromises inherent in that system) and doesn't really give you a power advantage - most of the technology efforts in LPG development has been in getting them to compete in terms of power to efficiency figures. Intercoolers are a definite power add in terms of net energy usage, LPG is not at present. Yes, on paper it looks like it is, but the extra weight and energy requirements just allow you to use an alternative fuel rather than gain power.
posted by Brockles at 8:12 PM on January 17, 2011
@onya: I meant that LPG is not widely available in many North American markets. At present there is only one factory CNG-powered car available here (a Honda Civic variant). Due to the lack of availability, OEMs are not inclined to design their cars to run on that fuel... unless it gives a CAFE advantage like E85. Incidentally, ethanol is attractive for charge cooling due to its extremely high latent heat of vaporization compared to gasoline.
In my excitement about a car-related thermodynamics question I didn't even come close to answering the OP's question, so here goes. The numbers you are interested in are the latent heat of vaporization of liquid propane and the specific heat capacity of gaseous propane (at ~25psia) and the specific heat capacity of air at ~25psia. You would also need to know the stoichiometric fuel/air ratio for LPG or whatever other fuel you are interested in.
The incoming air is at an elevated temperature. It transfers energy to vaporize the fuel. The fuel vaporizes then the energy transfer from the air to the fuel continues until they reach a common temperature. The first part of the energy transfer to the fuel takes place at constant temperature, during the fuel's phase change. This is the latent heat of vaporization. The second part of the energy transfer takes place at ~constant pressure. Assuming good mixing this is a relatively straightforward problem to work out numerically but I don't have access to reliable figures on my gf's laptop. I will post a numerical example tomorrow from my office where I have access to more reliable data than Wolfram, ETB and Wikipedia.
I think I know what issue Brockles is alluding to. One issue that interferes with fuel-based charge cooling (as opposed to an intercooler or other refrigerant loop) is that you are required to use a stoichiometric fuel/air blend. This is necessary so that the 3-way catalyst can appropriately oxidize unburned fuel, carbon dioxide and reduce NOx emissions. Current 3-way catalysts don't work well with excess air or rich mixtures. If the fuel required for the given amount of air can't charge cool it enough then you don't reap any benefit or exploit any synergy that outstrip the advantage of liquid fuels.
In a big picture sense, the LPG is just storing the energy that was consumed to compress it in the first place. The "cooling effect" is just a sort of refrigeration at a distance. It wasn't free.
posted by KevCed at 8:35 PM on January 17, 2011 [1 favorite]
In my excitement about a car-related thermodynamics question I didn't even come close to answering the OP's question, so here goes. The numbers you are interested in are the latent heat of vaporization of liquid propane and the specific heat capacity of gaseous propane (at ~25psia) and the specific heat capacity of air at ~25psia. You would also need to know the stoichiometric fuel/air ratio for LPG or whatever other fuel you are interested in.
The incoming air is at an elevated temperature. It transfers energy to vaporize the fuel. The fuel vaporizes then the energy transfer from the air to the fuel continues until they reach a common temperature. The first part of the energy transfer to the fuel takes place at constant temperature, during the fuel's phase change. This is the latent heat of vaporization. The second part of the energy transfer takes place at ~constant pressure. Assuming good mixing this is a relatively straightforward problem to work out numerically but I don't have access to reliable figures on my gf's laptop. I will post a numerical example tomorrow from my office where I have access to more reliable data than Wolfram, ETB and Wikipedia.
I think I know what issue Brockles is alluding to. One issue that interferes with fuel-based charge cooling (as opposed to an intercooler or other refrigerant loop) is that you are required to use a stoichiometric fuel/air blend. This is necessary so that the 3-way catalyst can appropriately oxidize unburned fuel, carbon dioxide and reduce NOx emissions. Current 3-way catalysts don't work well with excess air or rich mixtures. If the fuel required for the given amount of air can't charge cool it enough then you don't reap any benefit or exploit any synergy that outstrip the advantage of liquid fuels.
In a big picture sense, the LPG is just storing the energy that was consumed to compress it in the first place. The "cooling effect" is just a sort of refrigeration at a distance. It wasn't free.
posted by KevCed at 8:35 PM on January 17, 2011 [1 favorite]
The other commenters have gone over a lot of the material, but I'll just throw in what I've seen in the high-performance aftermarket realm.
First, your goal (cooling the charge with the fuel) is actually one of the biggest benefits of using nitrous oxide as a supplementary oxidizing agent. "Spraying" into the intercooler can have far greater gains than in a normally-aspirated application for just the reasons you're considering.
As well, using LPG in a "dual-fuel" setup is pretty common with diesels. There's a point at which heat from compression starts becoming a problem in diesel applications; LPG allows you to cool your intake charge and up your supercharging pressure even further.
posted by TheNewWazoo at 9:00 PM on January 17, 2011
First, your goal (cooling the charge with the fuel) is actually one of the biggest benefits of using nitrous oxide as a supplementary oxidizing agent. "Spraying" into the intercooler can have far greater gains than in a normally-aspirated application for just the reasons you're considering.
As well, using LPG in a "dual-fuel" setup is pretty common with diesels. There's a point at which heat from compression starts becoming a problem in diesel applications; LPG allows you to cool your intake charge and up your supercharging pressure even further.
posted by TheNewWazoo at 9:00 PM on January 17, 2011
Take the supercharger out of the equation to simplify things. (All it does is give the engine more displacement, or a higher compression ratio, depending on how you look at it.)
So, how much heat does it take to vaporize gasoline versus propane? I think the key here will be that the propane wants to be vaporized and gasoline doesn't, at STP. The propane already has (much of) the necessary heat in it, it is being kept liquid by the high pressure. So I think that you are not going to get what you want out of the propane.
There is also the air to fuel ratio. I have no idea what the masses are, but I bet that has something to do with it. There probably just isn't enough "cooling power" in the fuel to make a difference.
Regardless, the heat is still in the engine and not somewhere else.
If I'm not mistaken, you want your air charge as cool as possible so that it is more dense. So you can cram more fuel and O2 molecules into the cylinder so you get a bigger bang. So if you cool the charge inside, or almost inside, the combustion chamber, you really aren't getting more air/fuel in there.
posted by gjc at 9:24 PM on January 17, 2011
So, how much heat does it take to vaporize gasoline versus propane? I think the key here will be that the propane wants to be vaporized and gasoline doesn't, at STP. The propane already has (much of) the necessary heat in it, it is being kept liquid by the high pressure. So I think that you are not going to get what you want out of the propane.
There is also the air to fuel ratio. I have no idea what the masses are, but I bet that has something to do with it. There probably just isn't enough "cooling power" in the fuel to make a difference.
Regardless, the heat is still in the engine and not somewhere else.
If I'm not mistaken, you want your air charge as cool as possible so that it is more dense. So you can cram more fuel and O2 molecules into the cylinder so you get a bigger bang. So if you cool the charge inside, or almost inside, the combustion chamber, you really aren't getting more air/fuel in there.
posted by gjc at 9:24 PM on January 17, 2011
Response by poster: Thanks for the answers so far everyone, let me attempt to clarify some issues:
1. LPG is very widely available in Australia. It's a much cheaper source of fuel for us (roughly half the cost of petrol).
2. Due to its availability, there are hundreds of thousands of cars with an LPG system already installed (including mine, of course!). The vast majority of those cars use a converter to facilitate the phase change from liquid to gas, and then a carburettor/throttle body to mix the air and fuel in the correct ratio.
3. The compression of the fuel is performed by the petroleum company long before it gets pumped into the car. We don't have to "pay" (in energy or money) to receive it in liquid form.
4. "If I'm not mistaken, you want your air charge as cool as possible so that it is more dense." Correct. That is the whole and sole goal of this experiment.
5. gjc is probably right, for the purposes of the thought experiment we can probably remove the supercharger, and we can also assume that the ideal air/fuel ratio is 14:1.
I guess the simplest possible form of this question is:
Will the vaporisation of 1 unit of LPG reduce the temperature of 14 units of air by an appreciable amount?
posted by autocol at 10:52 PM on January 17, 2011
1. LPG is very widely available in Australia. It's a much cheaper source of fuel for us (roughly half the cost of petrol).
2. Due to its availability, there are hundreds of thousands of cars with an LPG system already installed (including mine, of course!). The vast majority of those cars use a converter to facilitate the phase change from liquid to gas, and then a carburettor/throttle body to mix the air and fuel in the correct ratio.
3. The compression of the fuel is performed by the petroleum company long before it gets pumped into the car. We don't have to "pay" (in energy or money) to receive it in liquid form.
4. "If I'm not mistaken, you want your air charge as cool as possible so that it is more dense." Correct. That is the whole and sole goal of this experiment.
5. gjc is probably right, for the purposes of the thought experiment we can probably remove the supercharger, and we can also assume that the ideal air/fuel ratio is 14:1.
I guess the simplest possible form of this question is:
Will the vaporisation of 1 unit of LPG reduce the temperature of 14 units of air by an appreciable amount?
posted by autocol at 10:52 PM on January 17, 2011
Will the vaporisation of 1 unit of LPG reduce the temperature of 14 units of air by an appreciable amount?
If I am getting the slant of your question correct, it won't be able to make any difference. The air is already inside the combustion chamber at that stage so you are dealing with a fixed volume of LPG and a fixed volume of (compressed or not, depending on supercharger) charge air. So the vaporisation won't give any advantage from cooling the air anyway because it won't allow the usual advantage (increased air volume in the cylinder) because the valves are shut. No more air can get in, so you're just cooling (to whatever degree) a fixed volume of air that will just get heated by the burn in a couple of milliseconds anyway.
posted by Brockles at 7:26 AM on January 18, 2011
If I am getting the slant of your question correct, it won't be able to make any difference. The air is already inside the combustion chamber at that stage so you are dealing with a fixed volume of LPG and a fixed volume of (compressed or not, depending on supercharger) charge air. So the vaporisation won't give any advantage from cooling the air anyway because it won't allow the usual advantage (increased air volume in the cylinder) because the valves are shut. No more air can get in, so you're just cooling (to whatever degree) a fixed volume of air that will just get heated by the burn in a couple of milliseconds anyway.
posted by Brockles at 7:26 AM on January 18, 2011
Best answer: In what follows, I used the following subscripts, hopefully with some continuity
a=air
f=fuel
l=liquid
g=gas
b=boiling
p=constant pressure (for specific heat capacity)
fg=boiling phase change
ma*cp,a*(Ta,in-Ta,out) = mf*[cpf,g*(Tf,out-Tb,f)+hfg,f+cpf,l*(Tb,f-Tf,in)]
The above is the energy balance I described. The change in temperature of the air is equal to the change in enthalpy of the fuel. The first c*ΔT term in the square brackets is the sensible change from boiling to the final mixture temperature. The second term is the latent heat of vaporization of the fuel. The second c*ΔT term (the third term) in the square brackets is the sensible change of liquid fuel from input temperature to boiling temperature.
If we assume that Ta,out=Tf,out=Tout and we use the following physical properties from Heywood's book on IC engines
(mf/ma)stoich.=0.0638
hfg,f= 426 kJ/kg
cpf,l= 0.63 kJ/(kg*K)
cpf,g= 2.2 kJ/(kg*K)
cp,a= 1.0 kJ/kg*K
Tb,f= 231 K (at atmospheric pressure)
Using Ta,in= 350 K = 77°C (seems reasonable for post-compressor)
Assume Tf,in is 25 degrees below boiling. The amount below boiling (in the intake) will be proportional to the pressure the LPG is under. The colder the LPG is coming in, the colder the air will be. However, the sensible change due to this is significantly smaller than the phase change (hfg,f is 200x greater than cpf,l).
Solving for Tout= {cp,aTa,in-(F/A)stoich.*[hfg,f+cpf,l(Tb,f-Tf,in)-cpf,g*Tbf]}/{cp,a+(F/A)stoich.*cpf,g}. Note that by dividing through by amount of fuel and air this assumes only the stoichiometric ratio, not any particular unit of air. (I think this is what you want, could one unit of fuel cool the appropriate amount of air)
Tout=310K = 37°C. Or, in other words a potential for a ΔT of ~40°. However, gasoline liquid evaporation shows comparable capacity for charge cooling. In practice, much of the heat of vaporization comes actually from the intake port walls, not from the charge. In such a case the realized charge cooling would be less.
Incidentally, even if LPG came into the engine at absolute zero, Tout would be 303K, which emphasizes my point that phase change is the dominant cooling mechanism.
I hope this answers your questions, and that my effort to type it up was clear enough.
posted by KevCed at 7:40 AM on January 18, 2011
a=air
f=fuel
l=liquid
g=gas
b=boiling
p=constant pressure (for specific heat capacity)
fg=boiling phase change
ma*cp,a*(Ta,in-Ta,out) = mf*[cpf,g*(Tf,out-Tb,f)+hfg,f+cpf,l*(Tb,f-Tf,in)]
The above is the energy balance I described. The change in temperature of the air is equal to the change in enthalpy of the fuel. The first c*ΔT term in the square brackets is the sensible change from boiling to the final mixture temperature. The second term is the latent heat of vaporization of the fuel. The second c*ΔT term (the third term) in the square brackets is the sensible change of liquid fuel from input temperature to boiling temperature.
If we assume that Ta,out=Tf,out=Tout and we use the following physical properties from Heywood's book on IC engines
(mf/ma)stoich.=0.0638
hfg,f= 426 kJ/kg
cpf,l= 0.63 kJ/(kg*K)
cpf,g= 2.2 kJ/(kg*K)
cp,a= 1.0 kJ/kg*K
Tb,f= 231 K (at atmospheric pressure)
Using Ta,in= 350 K = 77°C (seems reasonable for post-compressor)
Assume Tf,in is 25 degrees below boiling. The amount below boiling (in the intake) will be proportional to the pressure the LPG is under. The colder the LPG is coming in, the colder the air will be. However, the sensible change due to this is significantly smaller than the phase change (hfg,f is 200x greater than cpf,l).
Solving for Tout= {cp,aTa,in-(F/A)stoich.*[hfg,f+cpf,l(Tb,f-Tf,in)-cpf,g*Tbf]}/{cp,a+(F/A)stoich.*cpf,g}. Note that by dividing through by amount of fuel and air this assumes only the stoichiometric ratio, not any particular unit of air. (I think this is what you want, could one unit of fuel cool the appropriate amount of air)
Tout=310K = 37°C. Or, in other words a potential for a ΔT of ~40°. However, gasoline liquid evaporation shows comparable capacity for charge cooling. In practice, much of the heat of vaporization comes actually from the intake port walls, not from the charge. In such a case the realized charge cooling would be less.
Incidentally, even if LPG came into the engine at absolute zero, Tout would be 303K, which emphasizes my point that phase change is the dominant cooling mechanism.
I hope this answers your questions, and that my effort to type it up was clear enough.
posted by KevCed at 7:40 AM on January 18, 2011
@Brockles: The advantage of charge cooling is increased density for more power, but it can also mitigate engine knock. That can allow more aggressive (or even just closer-to-optimal) spark timing, or more boost pressure. This means that a cooler charge can improve efficiency or power even if it does not directly increase the amount of charge in-cylinder.
posted by KevCed at 7:43 AM on January 18, 2011
posted by KevCed at 7:43 AM on January 18, 2011
Response by poster: KevCed, brilliant work!
I don't know how you managed to type out an equation so beautifully on the web, I can never get it to look how I want it to!
A change in temperature of 40 degrees is beyond my expectations by quite a bit. I'd imagine by the time the inefficiencies of the cooling system are accounted for, the real world change might be closer to 20 degrees, but that's still enough to make a significant difference to the power output of the engine.
I'm going to make one. Thanks very much for your help.
Brockles, the vaporisation of the LPG takes place in a seperate unit, before it is introduced to the intake charge. (This is not a direct liquid injection system, though they are starting to appear). The vaporisation will be used to cool a body of fluid, which via an intercooler will cool the intake charge. Make sense?
posted by autocol at 3:52 PM on January 18, 2011
I don't know how you managed to type out an equation so beautifully on the web, I can never get it to look how I want it to!
A change in temperature of 40 degrees is beyond my expectations by quite a bit. I'd imagine by the time the inefficiencies of the cooling system are accounted for, the real world change might be closer to 20 degrees, but that's still enough to make a significant difference to the power output of the engine.
I'm going to make one. Thanks very much for your help.
Brockles, the vaporisation of the LPG takes place in a seperate unit, before it is introduced to the intake charge. (This is not a direct liquid injection system, though they are starting to appear). The vaporisation will be used to cool a body of fluid, which via an intercooler will cool the intake charge. Make sense?
posted by autocol at 3:52 PM on January 18, 2011
It was my pleasure, however I must issue the following disclaimer:
I am a mechanical engineer but I don't endorse the construction of the propane charge cooler. My assistance with calculations was for illustration purposes. Any subsequent use of my comments is undertaken at your own risk.
I would be extremely careful to avoid potential backflow of propane when the engine is operating at low manifold air pressure (i.e. negligible boost). It is easy to become complacent with automotive fuels. The reason we're hooked on hydrocarbon fuels is that they have truly staggering energy density, around 40-50 MJ/kg for most liquid hydrocarbons. When you fill up your car there is a ~10MW flow of energy going through the filler nozzle. (i.e. chemical enthalpy). On their own hydrocarbons are actually pretty stable, which is why they persist in the ground for millions of years "awaiting" extraction. When mixed with a suitable oxidizer, like a hot post-compressor air flow they become very willing to react. I advise caution.
Also: I used the sub tags to pretty it up for web consumption.
I might not be completely opposed to hearing how it turns out.
posted by KevCed at 5:02 PM on January 18, 2011
I am a mechanical engineer but I don't endorse the construction of the propane charge cooler. My assistance with calculations was for illustration purposes. Any subsequent use of my comments is undertaken at your own risk.
I would be extremely careful to avoid potential backflow of propane when the engine is operating at low manifold air pressure (i.e. negligible boost). It is easy to become complacent with automotive fuels. The reason we're hooked on hydrocarbon fuels is that they have truly staggering energy density, around 40-50 MJ/kg for most liquid hydrocarbons. When you fill up your car there is a ~10MW flow of energy going through the filler nozzle. (i.e. chemical enthalpy). On their own hydrocarbons are actually pretty stable, which is why they persist in the ground for millions of years "awaiting" extraction. When mixed with a suitable oxidizer, like a hot post-compressor air flow they become very willing to react. I advise caution.
Also: I used the sub tags to pretty it up for web consumption.
I might not be completely opposed to hearing how it turns out.
posted by KevCed at 5:02 PM on January 18, 2011
One thing to consider is low temperature operation at low boost levels - will there still be enough energy to prevent freeze-up?
Years ago I was running a dual-fuel vehicle and one cold morning set off and switched [too soon as it turned out] to LPG [we usually started on petrol]. As we'd switched to LPG before the engine coolant was warmed up, we froze the vaporizer into a solid block of ice.
You may need to consider this sort of thing if you end up idling for an extended period in low temperatures.
posted by HiroProtagonist at 5:42 PM on January 19, 2011
Years ago I was running a dual-fuel vehicle and one cold morning set off and switched [too soon as it turned out] to LPG [we usually started on petrol]. As we'd switched to LPG before the engine coolant was warmed up, we froze the vaporizer into a solid block of ice.
You may need to consider this sort of thing if you end up idling for an extended period in low temperatures.
posted by HiroProtagonist at 5:42 PM on January 19, 2011
Response by poster: KevCed, fortunately I will not be manufacturing (nor tampering with) any of the equipment that actually processes the fuel. The entire fuel vaporisation and delivery system is a professionally installed system that is already in-situ in the vehicle. All I will be doing is introducing a water-to-air intercooler between the supercharger and the throttle-body, and plumbing the water through the converter instead of radiator fluid.
Also, I promise not to blow myself up.
I also promise to let you know what happens. That may not be for six months :)
(You know, life and stuff!).
posted by autocol at 7:34 PM on January 19, 2011
Also, I promise not to blow myself up.
I also promise to let you know what happens. That may not be for six months :)
(You know, life and stuff!).
posted by autocol at 7:34 PM on January 19, 2011
Response by poster: Hiro, an excellent point and one I had indeed considered.
One of my favourite features of LPG powered cars is that, in the event of a cracked radiator resulting in fluid loss, usually the converter freezes over before the engine is damaged by overheating! I should know, it's happened to me twice.
I'm not sure if it will be possible to calculate if this will be a problem in other way other than simply giving it a try. One solution if it does pose a problem would be to introduce a thermostat of some sort that opens at low temperatures, allowing a bit of warm radiator fluid into the cooling system if the converter is likely to freeze up.
Hopefully that's not going to be necessary, as it just adds another level of complexity I'd like to avoid. Still, it was a good point, thank you.
posted by autocol at 7:38 PM on January 19, 2011
One of my favourite features of LPG powered cars is that, in the event of a cracked radiator resulting in fluid loss, usually the converter freezes over before the engine is damaged by overheating! I should know, it's happened to me twice.
I'm not sure if it will be possible to calculate if this will be a problem in other way other than simply giving it a try. One solution if it does pose a problem would be to introduce a thermostat of some sort that opens at low temperatures, allowing a bit of warm radiator fluid into the cooling system if the converter is likely to freeze up.
Hopefully that's not going to be necessary, as it just adds another level of complexity I'd like to avoid. Still, it was a good point, thank you.
posted by autocol at 7:38 PM on January 19, 2011
This thread is closed to new comments.
This is possible but not widely used at the present for a few reasons:
1) LPG is not widely available as an automotive fuel. It's an infrastructure issue and LPG is restricted from use in some parking structures I have heard
2) Gaseous fuels have lower volumetric energy density than liquid fuels. This reduces vehicle range
3) Gaseous fuel engines can suffer from reduced output because the gaseous fuel displaces some air in the charge in a way that liquid fuels don't. This is part of the reason to use a forced induction strategy like turbo- or supercharging.
The basic idea of fuel evporation for charge cooling is one of the primary motives for the move to gasoline direct injection.
With higher CAFE standards you'll see more downsized, turbocharged engines and I believe more LPG for knock mitigation. Propane (and methane from CNG) have nice octane numbers and good emissions characteristics compared to many liquid fuels.
posted by KevCed at 7:54 PM on January 17, 2011