Post by firegremlin on Mar 8, 2024 18:01:30 GMT -5
I need some initial guidance for this project.
We have a lightweight (I expect ~1200lb or so in the end) racecar for 24 Hours of Lemons that I'm in the early process of caging. The stock motor is rare, weak, heavy, and I really don't want to become an expert in it; once it blows up, something else will go in.
Given the size and weight of the car, I've decided to build a turbine engine for it.
Budget: The engine has to be hella lemony, to stay in the general spirit of the event, so the more used and ugly parts I can get for it, the better. We don't get a lot of scrutiny for going way over budget on fun little projects like that, but this isn't a "50K worth of machining work" kind of build.
General layout: I'm thinking a pair of automotive turbochargers; one for the gas generator, and one (sans the cold section) for the power turbine. The power turbine will bolt to a "flat" reduction gearbox that will then bolt to the factory transmission. The gearbox will be a spur gear setup with a jackshaft. I also want to use a small-ish electric motor (10hp or so) to provide initial torque at lower RPM and to absorb some power off-throttle so I can keep the gas generator spooled up.
Human factors: It's mostly me, with a few extra hands here and there. Assume reasonable automotive/fab skills, and a solid set of related tools and parts. Sketching up simple parts and jigs to be 3d-printed or sent out for waterjet cutting is not a problem. Microcontrollers/coding/data collection is also not a problem. Machining inconel turbine wheels, cutting custom gears, or doing flow analysis and actual engineering is a problem, at least right now
Time: I have about a year. The first race is in September, and the car won't see the track again until early next year. It would be nice to have the turboshaft engine ready by then.
Question #1: What would be a good non-exotic combo for the two turbochargers? My experience with turbos so far has been trying to find a mild enough compressor coupled to a lazy turbine, so most of what I have sitting around at the shop is a pile of smaller Volvo turbochargers. Now (as I understand) I need something that'll be efficient at 3+ pressure ratio while pushing at least a pound a second. Again, target power output is ~35-70hp. I want the broadest useful RPM range from the power turbine - it's a 4-speed gearbox, and we go anywhere between 35mph to 100mph in cars like this on an average track.
Question #2: What's the best way to gear the power turbine? I'm thinking of taking something like this, press-fit onto the compressor shaft, plus a polished spacer tube. The spacer would go into the far wall of the gearbox with a 'pilot bushing' around it, and pressurized oil feed. The big gear's jackshaft would just use spray-lubricated ball bearings. Common sump and oil for the "pre-gearbox" and turbo oil feed. I'd like to top out at about 10000rpm output shaft speed.
Question #3: Is ~12 gallons per hour fuel burn remotely possible, or should I just fit the largest allowed fuel cell right away? Obviously, it won't be a competitive entry, but it'd be nice to stay on the track for at least an hour between refueling.
I *think* I can build the gas generator part following other projects, that part seems reasonably straightforward. I'm mostly worried about the gearbox and picking a well-matched pair of power turbine and gas generator turbocharger. Any suggestions are welcome!
We have a lightweight (I expect ~1200lb or so in the end) racecar for 24 Hours of Lemons that I'm in the early process of caging. The stock motor is rare, weak, heavy, and I really don't want to become an expert in it; once it blows up, something else will go in.
Given the size and weight of the car, I've decided to build a turbine engine for it.
Budget: The engine has to be hella lemony, to stay in the general spirit of the event, so the more used and ugly parts I can get for it, the better. We don't get a lot of scrutiny for going way over budget on fun little projects like that, but this isn't a "50K worth of machining work" kind of build.
General layout: I'm thinking a pair of automotive turbochargers; one for the gas generator, and one (sans the cold section) for the power turbine. The power turbine will bolt to a "flat" reduction gearbox that will then bolt to the factory transmission. The gearbox will be a spur gear setup with a jackshaft. I also want to use a small-ish electric motor (10hp or so) to provide initial torque at lower RPM and to absorb some power off-throttle so I can keep the gas generator spooled up.
Human factors: It's mostly me, with a few extra hands here and there. Assume reasonable automotive/fab skills, and a solid set of related tools and parts. Sketching up simple parts and jigs to be 3d-printed or sent out for waterjet cutting is not a problem. Microcontrollers/coding/data collection is also not a problem. Machining inconel turbine wheels, cutting custom gears, or doing flow analysis and actual engineering is a problem, at least right now
Time: I have about a year. The first race is in September, and the car won't see the track again until early next year. It would be nice to have the turboshaft engine ready by then.
Question #1: What would be a good non-exotic combo for the two turbochargers? My experience with turbos so far has been trying to find a mild enough compressor coupled to a lazy turbine, so most of what I have sitting around at the shop is a pile of smaller Volvo turbochargers. Now (as I understand) I need something that'll be efficient at 3+ pressure ratio while pushing at least a pound a second. Again, target power output is ~35-70hp. I want the broadest useful RPM range from the power turbine - it's a 4-speed gearbox, and we go anywhere between 35mph to 100mph in cars like this on an average track.
Question #2: What's the best way to gear the power turbine? I'm thinking of taking something like this, press-fit onto the compressor shaft, plus a polished spacer tube. The spacer would go into the far wall of the gearbox with a 'pilot bushing' around it, and pressurized oil feed. The big gear's jackshaft would just use spray-lubricated ball bearings. Common sump and oil for the "pre-gearbox" and turbo oil feed. I'd like to top out at about 10000rpm output shaft speed.
Question #3: Is ~12 gallons per hour fuel burn remotely possible, or should I just fit the largest allowed fuel cell right away?
Obviously, it won't be a competitive entry, but it'd be nice to stay on the track for at least an hour between refueling.I *think* I can build the gas generator part following other projects, that part seems reasonably straightforward. I'm mostly worried about the gearbox and picking a well-matched pair of power turbine and gas generator turbocharger. Any suggestions are welcome!
