I wrote a rant on Ethanol fuels ....

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5946

Yup Elvis, that does happen in todays world often enough. Sad

Dimitri

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5946

Paul ... just a update ... I got my SAE Automotive Engineering International in the mail today.

So they list for the Chevy Cruze:

Fuel energy theoretically:
Energy into the Piston = 38%
Energy wasted due to Exhaust and Coolant losses = 62%

BUT ...

Mechanical energy losses of the car:
Engine & pumping = 37%

This gives us 24% fuel energy efficiently out of the engine similar to what I was quoting before, a little better actually (verse 20% that I've heard modern engines are at), still nothing to brag about. But still a relative improvement.

Then the rest of the energy losses:
Electrical Loads = 3%
Drive Train and Chassis = 2%
Transmission and Final Drive = 18%
Tire Rolling Resistance = 12%
Aerodynamic Drag = 17%

So engine + everything else losses is 89% of the energy out of the fuel, out of the 38% theoretical maximum.

Leaving you with only 11% of the fuel energy that the pistons transfer in kinetic energy that moves the car, and allows to accelerate etc.

So the actual energy of the fuel that you end up actually using that is not due to efficiency losses, is a fraction of a percentage over 4%.

Dimitri

Elvis

still beats walking!!!...lol.

PaulS

Dimitri wrote:

Paul ... just a update ... I got my SAE Automotive Engineering International in the mail today.

So they list for the Chevy Cruze:

Fuel energy theoretically:
Energy into the Piston = 38%
Energy wasted due to Exhaust and Coolant losses = 62%

BUT ...

Mechanical energy losses of the car:
Engine & pumping = 37%

This gives us 24% fuel energy efficiently out of the engine similar to what I was quoting before, a little better actually (verse 20% that I've heard modern engines are at), still nothing to brag about. But still a relative improvement.

Then the rest of the energy losses:
Electrical Loads = 3% Under what conditions?
Drive Train and Chassis = 2% Under how much acceleration?
Transmission and Final Drive = 18% Under what acceleration / load?
Tire Rolling Resistance = 12% At what air pressure? how much weight? at what speed?
Aerodynamic Drag = 17% At what speed, altitude?

So engine + everything else losses is 89% of the energy out of the fuel, out of the 38% theoretical maximum.

Leaving you with only 11% of the fuel energy that the pistons transfer in kinetic energy that moves the car, and allows to accelerate etc.
So the actual energy of the fuel that you end up actually using that is not due to efficiency losses, is a fraction of a percentage over 4%.
4% for the efficiency of the entire vehicle but we were discussing the efficiency of the engine and how adding compression could improve it and what the effects of water injection (through whatever means) would have on the efficiency of the engine. NOT THE WHOLE VEHICLE.
Dimitri

Now, I must say that fuel is completely consumed so however the vehicle uses it there is no energy left over at all. It is all used up getting from point A to point B. The vehicle will use more gas going 100 miles at 150 mph then it would at 50 mph because it is more efficient at lower speeds down to about 40 - 45 mph depending on the drag coefficient, the weight being moved, and the specifics of the engine and fuel being used.
You used up all those words to confuse the issue and never addressed one point that I made - done!

I thought you were an engineer not a politician. HP = PLAN/33000
Pressure x Length of stroke in feet x Area of cylinder x Number of power strokes per minute /33000
That formula is in every mechanical engineering manual I have ever seen be it Kent's or Perry's or any other that I have read. Without doing anything else but increasing the pressure the engine will make more power - all other things being equal. Above 16:1 compression there is a point of diminishing returns in that it takes closer to the same power to compress the gasses as you get from the added compression but it doesn't reach equalibrium past 21:1 compression ratios.

Chevrolet engines may not have been the best choice for this discussion because I don't like them but I will use your example. In the last 50 years Chevrolet has improved their engine and total vehicle efficiency by several percentage points. If they used modern technology they could improve efficiency even more but it is more expensive to use that technology and they are already having trouble making a profit. They still have that pesky bail-out loan to repay.

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5946

GM's figures for efficiency design, based on the same old "combined highway/city" style of testing that is so very common today.

Confuse what issue? The fact that water injected (aka fluid injection) has came and went in modern engines for both planes and cars? Things such as intercoolers were found to be better for production engines.

Fact is there is so much losses with the rest of the vehicle as GM's own data shows, that cranking up a engine from 24% to 26% fuel efficiency means very little if its even achievable with water injection.

Which is why a lot of the work now is being focused on things such as dual clutch transmissions on small cars, etc, as its easier to fix a mechanical system them squeeze every last fraction of a percent of efficiency out of the engines burn cycle which thermodynamics tends to get in the way of.

Dimitri

PaulS

Dimitri,
IF that actual efficiency of the Chevrolet engine is just a net value of 24% then making it just 5% more efficient is a gross gain of over 20% in the amount of fuel to move the vehicle because if you are actually moving the vehicle currently with 24% then a gross increase of 5% would be 20.8% increase in the amount of fuel to move the vehicle. So instead of getting just 17 mpg you could be getting 20.5mpg. By working at it from the other end you would have to remove much more losses amounting to 19.968% improvement in efficiency.
Maybe that is why Chevrolet needs a bailout and Ford doesn't.

Elvis

well a chevy or a ford would be just fine to go HUNTING in.....