I hope to buy my 9A kit soon and get started, I'm still in the process of researching all the particular parts and pieces associated with building my first aircraft before writing the check - including engine choices. I was talking the other day with a friend about the Thielert turbodiesel, and possibly using it in my aircraft. We started talking about the liquid cooling loop, and he had an idea about using a liquid-liquid heat exchanger to dump the heat from the coolant into the diesel fuel in the tanks, instead of using a draggy radiator. Then the fuel can dissipate the heat through the wet wing.
Initially, I see several issues with this, all of which could be dealt with by using some good analysis and careful engineering, and a couple real nice benefits. Coolant leaks, increased vapor pressure of the fuel, CG changes, failure modes and heat exchanger design jump up real big in my mind, but the more I think about it the more I can see design changes that could handle these issues. The loss of the radiator would mean a nice decrease in drag with a redesigned cowl, and it would look pretty cool to boot. I'm not too sure about this being thermodynamically feasible, though, so I'm asking for some additional input from some guys with more engineering knowledge than me before I waste any more dreamtime on this.
The coolant loop and oil cooler on this engine will need to dump roughly 160,000 btu/hr at full power. The fuel (pump diesel or Jet A) will be stable to about 300 F, so no issue there. The coolant is thermostatically controlled to 210F nominal, 250 max,and pressurized to 25 psig. A minimum quantity of fuel would obviously be required for adequate heat removal. Assuming a high flow, low pressure fuel pump drawing from the inboard end of the tank through a heat exchanger and returning to the far outboard point of a properly baffled tank, you can assume fairly decent thermal mixing and complete bottom tank skin exposure to the slipstream. The issue then becomes twofold. Can the tank skin dump that much heat in a worst-case-scenario of a hot day with a full-power climb (think extended touch and go session here, in summertime West Texas heat) and what kind of heat exchanger/pump setup would be needed to handle that heat flow?
For takeoff/climbout on a hot day, you can safely assume (especially with cool tanks) that you'll be effectively "storing" heat for the first 10 minutes or so in the fuel, to be dumped once you climb into cool air. What would be the equilibrium temp of the fuel at common cruise conditions, say 75% power(120,000 btu/hr heat rejection), 140ish kias, and 40F OAT?
At first blush, I thought this was a pretty cool idea. Then I started seeing the problems associated with it, and thought it was a disaster looking for place to happen. Then, the more I thought about it, I starting seeing solutions to the problems posed, and now I'm back to the point of thinking it just might be feasible from a design/engineering standpoint, if the heat flows work out. Any suggestions?
Initially, I see several issues with this, all of which could be dealt with by using some good analysis and careful engineering, and a couple real nice benefits. Coolant leaks, increased vapor pressure of the fuel, CG changes, failure modes and heat exchanger design jump up real big in my mind, but the more I think about it the more I can see design changes that could handle these issues. The loss of the radiator would mean a nice decrease in drag with a redesigned cowl, and it would look pretty cool to boot. I'm not too sure about this being thermodynamically feasible, though, so I'm asking for some additional input from some guys with more engineering knowledge than me before I waste any more dreamtime on this.
The coolant loop and oil cooler on this engine will need to dump roughly 160,000 btu/hr at full power. The fuel (pump diesel or Jet A) will be stable to about 300 F, so no issue there. The coolant is thermostatically controlled to 210F nominal, 250 max,and pressurized to 25 psig. A minimum quantity of fuel would obviously be required for adequate heat removal. Assuming a high flow, low pressure fuel pump drawing from the inboard end of the tank through a heat exchanger and returning to the far outboard point of a properly baffled tank, you can assume fairly decent thermal mixing and complete bottom tank skin exposure to the slipstream. The issue then becomes twofold. Can the tank skin dump that much heat in a worst-case-scenario of a hot day with a full-power climb (think extended touch and go session here, in summertime West Texas heat) and what kind of heat exchanger/pump setup would be needed to handle that heat flow?
For takeoff/climbout on a hot day, you can safely assume (especially with cool tanks) that you'll be effectively "storing" heat for the first 10 minutes or so in the fuel, to be dumped once you climb into cool air. What would be the equilibrium temp of the fuel at common cruise conditions, say 75% power(120,000 btu/hr heat rejection), 140ish kias, and 40F OAT?
At first blush, I thought this was a pretty cool idea. Then I started seeing the problems associated with it, and thought it was a disaster looking for place to happen. Then, the more I thought about it, I starting seeing solutions to the problems posed, and now I'm back to the point of thinking it just might be feasible from a design/engineering standpoint, if the heat flows work out. Any suggestions?