- #1
NTL2009
- 624
- 384
- TL;DR Summary
- For an automobile ICE, could gasoline be vaporized with a hot plate in a small chamber just before the intake valve to improve mpg at cruising speeds?
Here's a video by “driving 4 answers” who seems to me to be well versed on the details of Internal Combustion engines. The video does cover something that's a bit shrouded in 'conspiracy theory', and he touches on that, but of course for phys.org, I'm only interested in the actual science involved.
He analyzes the claim of achieving 100 mpg with a 427 cubic inch V8 1970 Ford Galaxy in 1977. Only the fuel supply system was modified. I was surprised that he feels the claim could have been realized. The car appears to vaporize the fuel (versus atomizing in a conventional carburetor or fuel injector). He claims a fully vaporized fuel is homogeneous, which burns faster and cleaner with no pockets of lean/rich, and can theoretically run lean, 40:1 ( versus a conventional ~ 22:1 limit ?). He doesn't mention, but I assume there is much lower throttle pumping loss for better mpg.
While he acknowledges it could be done, he says one drawback is very poor performance. I think because vaporized fuel takes up a large volume, so you can only get a relatively small amount of fuel in a cylinder, so limited power. And I think that is why a large V8 was used. That also makes sense from a Brake-Specific Fuel Consumption (BSFC) viewpoint - that big V8 running near open throttle and near full load (at reduced horsepower) would put the engine at an efficient part of the curve. Of course, you can get high mpg by trading acceleration and using a small conventional engine, but you wouldn't get the claimed advantages of fuel vaporization.
OK, so acceleration would be unacceptable. He goes on to say this could be addressed by using fuel injection to accelerate and start the engine, but he seems to poo-poo this as being too complex, and fuel vapors are unsafe. But I think he overstates this. Could there be a pre-combustion chamber on each cylinder, maybe the same volume of the cylinder, or somewhat larger, to hold a supply of vaporized fuel? I could envision a hot plate in that chamber (before the intake valve), and a fuel injector spraying a fine mist onto the hot plate to vaporize that fuel. It would supply just enough fuel for cruising power, the rest of the fuel for acceleration would be supplied by a separate injector that would not cool the plate. The fuel would have time to vaporize as it would be a continuous process. For a pre-combustion chamber the same size as the cylinder, assume 1800 RPM at cruise, at 2 revs per combustion, so 1800/60 = 30 revs/second, so ~ 1/15th of a second (67 ms) to vaporize the fuel. And at 100 mpg and 60 mph ( 1 mile-per-minute), that's 1/100th of a gallon per minute (let's switch to metric at this point!) or ~ 38 ml, divide by 4 cylinders, round to 10 ml, divide by 60 for 0.167 ml/second. I assume that would be do-able, but don't really know. I don't see where this would be a big safety issue, or overly complex.
A pre-combustion chamber would also address the issue he raises that not all components of the fuel vaporize at the same temperature. He claims these components would build up, and have to be drained collected - which would be impractical. But with the pre-combustion chamber, anything not fully vaporized would just be drawn into the engine in atomized form. I don't see a problem here. He seems to be envisioning a large chamber of vaporized fuel supplying all cylinders.
But, it seems we would still need a large displacement engine to get enough horsepower even for cruising speeds due to the volume of the vaporized fuel. That would be a major disadvantage. As I understand, 0.5 L per cylinder is a sort of practical limit for passenger cars engines, and moving to a V8 would be impractical in cost and size for most cars today. Would a supercharger be able to compensate for this, forcing more air/fuel into the cylinder, so maybe a 4 cylinder or V6 could work? Pollution control is another whole story.
Also, for reference, vaporization was used in some early stationary engines (“surface plate carburetor), so it's far from a new idea. But I also wonder, wouldn't running from propane or methane provide similar benefits as attributed to vaporizing gasoline? It's vapor already, right? And flex -fuel engines exist, but I never heard that they run higher efficiency on vapor?
This is really just a mental exercise / thought experiment. But that video made me very curious. Thoughts?
He analyzes the claim of achieving 100 mpg with a 427 cubic inch V8 1970 Ford Galaxy in 1977. Only the fuel supply system was modified. I was surprised that he feels the claim could have been realized. The car appears to vaporize the fuel (versus atomizing in a conventional carburetor or fuel injector). He claims a fully vaporized fuel is homogeneous, which burns faster and cleaner with no pockets of lean/rich, and can theoretically run lean, 40:1 ( versus a conventional ~ 22:1 limit ?). He doesn't mention, but I assume there is much lower throttle pumping loss for better mpg.
While he acknowledges it could be done, he says one drawback is very poor performance. I think because vaporized fuel takes up a large volume, so you can only get a relatively small amount of fuel in a cylinder, so limited power. And I think that is why a large V8 was used. That also makes sense from a Brake-Specific Fuel Consumption (BSFC) viewpoint - that big V8 running near open throttle and near full load (at reduced horsepower) would put the engine at an efficient part of the curve. Of course, you can get high mpg by trading acceleration and using a small conventional engine, but you wouldn't get the claimed advantages of fuel vaporization.
OK, so acceleration would be unacceptable. He goes on to say this could be addressed by using fuel injection to accelerate and start the engine, but he seems to poo-poo this as being too complex, and fuel vapors are unsafe. But I think he overstates this. Could there be a pre-combustion chamber on each cylinder, maybe the same volume of the cylinder, or somewhat larger, to hold a supply of vaporized fuel? I could envision a hot plate in that chamber (before the intake valve), and a fuel injector spraying a fine mist onto the hot plate to vaporize that fuel. It would supply just enough fuel for cruising power, the rest of the fuel for acceleration would be supplied by a separate injector that would not cool the plate. The fuel would have time to vaporize as it would be a continuous process. For a pre-combustion chamber the same size as the cylinder, assume 1800 RPM at cruise, at 2 revs per combustion, so 1800/60 = 30 revs/second, so ~ 1/15th of a second (67 ms) to vaporize the fuel. And at 100 mpg and 60 mph ( 1 mile-per-minute), that's 1/100th of a gallon per minute (let's switch to metric at this point!) or ~ 38 ml, divide by 4 cylinders, round to 10 ml, divide by 60 for 0.167 ml/second. I assume that would be do-able, but don't really know. I don't see where this would be a big safety issue, or overly complex.
A pre-combustion chamber would also address the issue he raises that not all components of the fuel vaporize at the same temperature. He claims these components would build up, and have to be drained collected - which would be impractical. But with the pre-combustion chamber, anything not fully vaporized would just be drawn into the engine in atomized form. I don't see a problem here. He seems to be envisioning a large chamber of vaporized fuel supplying all cylinders.
But, it seems we would still need a large displacement engine to get enough horsepower even for cruising speeds due to the volume of the vaporized fuel. That would be a major disadvantage. As I understand, 0.5 L per cylinder is a sort of practical limit for passenger cars engines, and moving to a V8 would be impractical in cost and size for most cars today. Would a supercharger be able to compensate for this, forcing more air/fuel into the cylinder, so maybe a 4 cylinder or V6 could work? Pollution control is another whole story.
Also, for reference, vaporization was used in some early stationary engines (“surface plate carburetor), so it's far from a new idea. But I also wonder, wouldn't running from propane or methane provide similar benefits as attributed to vaporizing gasoline? It's vapor already, right? And flex -fuel engines exist, but I never heard that they run higher efficiency on vapor?
This is really just a mental exercise / thought experiment. But that video made me very curious. Thoughts?
