Why does everyone rant and rave about the EcoBoost?

[KennyG]

Doesn't become more efficient, just makes more power. E85 is extremely tolerant of preignition and detonation. So you can crank the cylinder pressure way up, either with boost or mechanically.

Actually Egon is correct. We use words imprecisely sometimes, but the thermodynamic efficiency of the Otto cycle is directly dependent on compression ratio. Any change that increases the compression ratio will increase efficiency. If burning ethanol will allow an otherwise unchanged engine to have a higher compression ratio, the efficiency increases. If we use efficiency to mean how many gallons of fuel we use or if we use to mean how many horsepower we get from a BTU of fuel (two very different things) then a lot of other factors like cam and ignition timing come into the mix. As noted earlier, if we have to design the engine to operate on a number of different fuels, it quickly gets very complex which is why auto manufacturers have to spend so much on engineering and testing.

 

[MossRoad]

I did just that, twice. I will not purchase a new vehicle that is not E85. I hope that you own a FFV also !

I do. Its a 2013 Impala. And the only thing that has failed on it so far is the flex fuel sensor! We NEVER use E85.

Driving 50 miles to purchase less efficient fuel is just foolish. You'd spend 2-3 gallons just on the trip, probably more in a FF vehicle. Whats the point?

 

[ultrarunner]

Looks like my E85 is on the way just in time for the Iowa caucus...

Read in the paper that the President has increased the mandate above EPA recommendations...

The story also went on to say something like an early Christmas present for middle America.

 

[buickanddeere]

Actually Egon is correct. We use words imprecisely sometimes, but the thermodynamic efficiency of the Otto cycle is directly dependent on compression ratio. Any change that increases the compression ratio will increase efficiency. If burning ethanol will allow an otherwise unchanged engine to have a higher compression ratio, the efficiency increases. If we use efficiency to mean how many gallons of fuel we use or if we use to mean how many horsepower we get from a BTU of fuel (two very different things) then a lot of other factors like cam and ignition timing come into the mix. As noted earlier, if we have to design the engine to operate on a number of different fuels, it quickly gets very complex which is why auto manufacturers have to spend so much on engineering and testing.

Increasing the compression ratio does not increase efficiency . Increasing the expansion ratio is what increases efficiency .
More compression requires more power to build higher pressure . The higher pressure generates more heat which is wasted being absorbed by the water jacket. The higher air/fuel mixture just prior to ignition also reduces the delta T ratio which also reduces the delta P ratio .
The engine makes "power" on the pressure difference between the average mean pressure of the compression stroke vs the average mean pressure of the power stroke .

 

[Egon]

Increasing the compression ratio does not increase efficiency . Increasing the expansion ratio is what increases efficiency .
More compression requires more power to build higher pressure . The higher pressure generates more heat which is wasted being absorbed by the water jacket. The higher air/fuel mixture just prior to ignition also reduces the delta T ratio which also reduces the delta P ratio .
The engine makes "power" on the pressure difference between the average mean pressure of the compression stroke vs the average mean pressure of the power stroke .

Okay; what do we have to do to increase the difference between the average mean pressure's?

 

[tcartwri]

There's also a lot less power available per standard unit of ethanol.

 

[buickanddeere]

Okay; what do we have to do to increase the difference between the average mean pressure's?

Cam timing, valve size, intake runner flow capacity and throttle opening.
This is why commercial boilers control fresh air flow instead of operating wide open. A better example would be the occasional diesel and stationary gas turbines that can throttle airflow in at part load. Also why intercoolers are used after the compressor stages on gas some gas turbines . Intercoolers on turbo or supercharged reciprocating Otto cycle engines .

 

[KennyG]

Increasing the compression ratio does not increase efficiency . Increasing the expansion ratio is what increases efficiency .
More compression requires more power to build higher pressure . The higher pressure generates more heat which is wasted being absorbed by the water jacket. The higher air/fuel mixture just prior to ignition also reduces the delta T ratio which also reduces the delta P ratio .
The engine makes "power" on the pressure difference between the average mean pressure of the compression stroke vs the average mean pressure of the power stroke .

You are just playing with words. The thermodynamic efficiency of an internal combustion engine is directly a function of the compression ratio. For a standard Otto cycle engine the expansion ratio and compression ratio are the same. Here is a derivation of the Otto cycle efficiency: http://www.engr.colostate.edu/~allan/thermo/page5/page5.html

The BMEP differences during the cycle are direct results of the cycle shape and compression ratio. If the engine is running on a modified cycle (i.e. Atkinson or Diesel) the shapes are different but the efficiency is still a function of compression ratio. The Atkinson (Miller) cycle is interesting in that the expansion ratio is not the same as the compression ratio which allows efficiency to exceed the Otto cycle but increasing the compression ratio on an Atkinson cycle engine will still increase efficiency. I assume your comments are driven by the advantages of the Atkinson cycle but the lack of torque (peak pressure) at low engine speed restrict it's application to hybrids.

 

[buickanddeere]

I did not want to confuse people with the Atkinson cycle name . Now tell me who cruises at full power? Cruising and most driving takes place in light duty service in a range of 20-40% of Max rated power. This is where engines with variable cam timing can be Otto at wide open but Atkinson at cruise.

 

[Egon]

Cam timing, valve size, intake runner flow capacity and throttle opening.
This is why commercial boilers control fresh air flow instead of operating wide open. A better example would be the occasional diesel and stationary gas turbines that can throttle airflow in at part load. Also why intercoolers are used after the compressor stages on gas some gas turbines i. Intercoolers on turbo or supercharged reciprocating Otto cycle engines .

Think the fuel supply is also controlled on boilers with the oxygen lagging, or is it leading? Memory fails at times.