gasoline efficiency

[dragonstar57]

what if you supercooled the air intake ports?

that would allow increased density of 02 in the engine so wouldn't that increase efficiency?

[Dekan]

what if you supercooled the air intake ports?

that would allow increased density of 02 in the engine so wouldn't that increase efficiency?

 

Is there a theoretical, or practical, limit to how efficient a gasoline engine can be - I mean if it's a car engine.

 

Suppose the engine only uses "regular" gasoline. No high-energy fuel additives like borane. And the engine is confined to breathing normal atmospheric air - ie no pure oxygen artificially bled into its intakes. (Supercooling would be allowed, if the engine itself generated the power to supercool its intakes - but would that make sense thermodynamically)

 

How many mpg could such an engine provide?

 

Bearing in mind, that the engine has to be in a car which is a practical consumer-product. Say a 4/5-seater car, capable of a reasonable cruising speed, like 60mph. And able to run up reasonably steep hills without stalling.

[dragonstar57]

Is there a theoretical, or practical, limit to how efficient a gasoline engine can be - I mean if it's a car engine.

 

Suppose the engine only uses "regular" gasoline. No high-energy fuel additives like borane. And the engine is confined to breathing normal atmospheric air - ie no pure oxygen artificially bled into its intakes. (Supercooling would be allowed, if the engine itself generated the power to supercool its intakes - but would that make sense thermodynamically)

 

How many mpg could such an engine provide?

 

Bearing in mind, that the engine has to be in a car which is a practical consumer-product. Say a 4/5-seater car, capable of a reasonable cruising speed, like 60mph. And able to run up reasonably steep hills without stalling.

my thinking was it could become part of the existing air-conditioning system and that might increase mpg by perhaps as much as 5.

it seems like it would make a pretty big difference

[PaulS1950]

Cooling the intake air makes it denser, requiring more fuel to keep the mixture right for burning. It increases power but decreases mileage.

Keeping the intake air at close to 200F will do a better job of providing good mileage and if the engine is designed for the specific rpm range in use you can get fairly good mileage. Lets say we need to run between 20 and 70 mph and that we have electronic fuel injection. An engine with high compression (around 9 - 10:1) will make better use of the fuel it consumes by compressing the mixture for more efficient burning and more extracted heat. With a four speed transmission (manual or auto with locking converter) where 3rd is 1:1 and 4th is .75:1 (overdrive) you could use a rear gear ratio of 2.80 - 3:1 and tune a moderate sized engine at 2000 rpm to get good mileage on the highway in overdrive and still get reasonable performance and mileage around town in second and third gear. Keeping engine temps around 200 to 250F and the intake charge at 200F using 10w-30 synthetic oil in an engine that reduces internal friction and you would get near the best that is possible through exhaustive tuning of the injection parameters and engine management (ignition and valve timing).

Other factors are tire pressure, alignment settings, weight of vehicle and driver and the largest factor of all, the driver. Gradual acceleration and decelleration, long following distances so you don't have to use your brakes often or hard will go a long way to increase the mileage in any vehicle.

[dragonstar57]

Cooling the intake air makes it denser, requiring more fuel to keep the mixture right for burning. It increases power but decreases mileage.

Keeping the intake air at close to 200F will do a better job of providing good mileage and if the engine is designed for the specific rpm range in use you can get fairly good mileage. Lets say we need to run between 20 and 70 mph and that we have electronic fuel injection. An engine with high compression (around 9 - 10:1) will make better use of the fuel it consumes by compressing the mixture for more efficient burning and more extracted heat. With a four speed transmission (manual or auto with locking converter) where 3rd is 1:1 and 4th is .75:1 (overdrive) you could use a rear gear ratio of 2.80 - 3:1 and tune a moderate sized engine at 2000 rpm to get good mileage on the highway in overdrive and still get reasonable performance and mileage around town in second and third gear. Keeping engine temps around 200 to 250F and the intake charge at 200F using 10w-30 synthetic oil in an engine that reduces internal friction and you would get near the best that is possible through exhaustive tuning of the injection parameters and engine management (ignition and valve timing).

Other factors are tire pressure, alignment settings, weight of vehicle and driver and the largest factor of all, the driver. Gradual acceleration and decelleration, long following distances so you don't have to use your brakes often or hard will go a long way to increase the mileage in any vehicle.

the idea of having to add more gas seems flawed as the normally unburned gas will 02 to react with and less gas could be used to remove heat problems

[CaptainPanic]

Supercooling your air inlet is a little pointless, because your refrigeration cycle will completely ruin the fuel economy of your car. Also, if you look at the formula of the Carnot efficiency of a heat engine, then you might notice that it only matters what your high temperature is (the hot reservoir, the combustion) and what the temperature of your cooling (the cold reservoir, which is the outside air) is. For Carnot, it is not relevant that you supercool your air first, as this happens within the system, and is therefore irrelevant.

 

Actually, the engine itself might be more efficient if you use the supercooled air as a cold reservoir, but if you look at the whole system, then your only cold reservoir is the outside air.

[dragonstar57]

it seems that this conversations has several assumptions going on.

1. I an assuming that there is un-combusted fuel leaving with the exhaust

2. it seems some are assuming that either their is no unburned fuel or that supplying with more/denser 02 supplies would either not burn the unburned fuel or doing so would not improve efficiency

there are many threads where someone comes up with an idea of how to get more 02 to the engine and thinks that it would improve efficiency and everyone says it wont work. can someone explain why extracting more energy from a given amount of fuel would not increase efficiency?