E3 spark plugs, will you save gas?
Omnia Gloria Fugit
Joined: May 2007
Posts: 744
From: College Station Texas
Re: E3 spark plugs, will you save gas?
Compression ratio is a calculated value based on combustion chamber volume, head gasket thickness to the previous plus the cylinder volume. Compression is determined mainly by the cam timing. They are two different things not related except by the word compression.
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Joined: Aug 2007
Posts: 215
Re: E3 spark plugs, will you save gas?
I almost hate to jump into this one, but since I've taken college course in Internal Combustion Engine design, I feel like I have to. There are some real terminology problems here.
Compression ratio a simple ratio of the maximum to minimum volume of the cylinder during the cycle. Nothing to do with timing or Otto/Atkinson/Diesel cycle as some have pointed out.
"Compression" is really meaningless. We've always used this in the shop to refer to the peak pressure recorded on the instrument during a "compression test" but what is really being measured is peak pressure.
Peak pressure will be affected by compression ratio but is also affected by valve timing when it varies as significantly from the ideal Otto cycle as the Atkinson cycle does. The real key parameter is Brake Mean Effective Pressure (BMEP) which is an expression of the average pressure force on the piston throughout the power cycle. BMEP directly converts to Horsepower at a given RPM.
The Atkinson cycle engine effectively has asymetrical compression. The effective compression ratio is lower than the physical ratio because the intake valve is held open. However, the expansion ration is still high because the exhaust valve is not opened early. This increases efficiency at the expense of power because the BMEP is reduced.
Compression ratio a simple ratio of the maximum to minimum volume of the cylinder during the cycle. Nothing to do with timing or Otto/Atkinson/Diesel cycle as some have pointed out.
"Compression" is really meaningless. We've always used this in the shop to refer to the peak pressure recorded on the instrument during a "compression test" but what is really being measured is peak pressure.
Peak pressure will be affected by compression ratio but is also affected by valve timing when it varies as significantly from the ideal Otto cycle as the Atkinson cycle does. The real key parameter is Brake Mean Effective Pressure (BMEP) which is an expression of the average pressure force on the piston throughout the power cycle. BMEP directly converts to Horsepower at a given RPM.
The Atkinson cycle engine effectively has asymetrical compression. The effective compression ratio is lower than the physical ratio because the intake valve is held open. However, the expansion ration is still high because the exhaust valve is not opened early. This increases efficiency at the expense of power because the BMEP is reduced.
Pretty Darn Active Enthusiast
Joined: Jun 2007
Posts: 311
From: Dry Heat, AZ
Re: E3 spark plugs, will you save gas?
I almost hate to jump into this one, but since I've taken college course in Internal Combustion Engine design, I feel like I have to. There are some real terminology problems here.
Compression ratio a simple ratio of the maximum to minimum volume of the cylinder during the cycle.
Nothing to do with timing or Otto/Atkinson/Diesel cycle as some have pointed out.
"Compression" is really meaningless. We've always used this in the shop to refer to the peak pressure recorded on the instrument during a "compression test" but what is really being measured is peak pressure.
Peak pressure will be affected by compression ratio but is also affected by valve timing when it varies as significantly from the ideal Otto cycle as the Atkinson cycle does. The real key parameter is Brake Mean Effective Pressure (BMEP) which is an expression of the average pressure force on the piston throughout the power cycle. BMEP directly converts to Horsepower at a given RPM.
The Atkinson cycle engine effectively has asymetrical compression. The effective compression ratio is lower than the physical ratio because the intake valve is held open. However, the expansion ration is still high because the exhaust valve is not opened early. This increases efficiency at the expense of power because the BMEP is reduced.
Compression ratio a simple ratio of the maximum to minimum volume of the cylinder during the cycle.
Nothing to do with timing or Otto/Atkinson/Diesel cycle as some have pointed out.
"Compression" is really meaningless. We've always used this in the shop to refer to the peak pressure recorded on the instrument during a "compression test" but what is really being measured is peak pressure.
Peak pressure will be affected by compression ratio but is also affected by valve timing when it varies as significantly from the ideal Otto cycle as the Atkinson cycle does. The real key parameter is Brake Mean Effective Pressure (BMEP) which is an expression of the average pressure force on the piston throughout the power cycle. BMEP directly converts to Horsepower at a given RPM.
The Atkinson cycle engine effectively has asymetrical compression. The effective compression ratio is lower than the physical ratio because the intake valve is held open. However, the expansion ration is still high because the exhaust valve is not opened early. This increases efficiency at the expense of power because the BMEP is reduced.
But ABSOLUTELY the DCR depends on cam timing! And DCR is the only meaningful compression ratio. Detonation happens due to the DCR, nothing to do with SCR or just CR as you have defined. Unless, of course, they work out to be the same. BMEP will not tell you if you need premium to avoid detonation, DCR will. And that was the point of this discussion.
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Joined: Mar 2006
Posts: 1,401
Re: E3 spark plugs, will you save gas?
Yes, your definition of CR is exactly what I defined as SCR. It is an essentially meaningless engine parameter.
But ABSOLUTELY the DCR depends on cam timing! And DCR is the only meaningful compression ratio. Detonation happens due to the DCR, nothing to do with SCR or just CR as you have defined. Unless, of course, they work out to be the same. BMEP will not tell you if you need premium to avoid detonation, DCR will. And that was the point of this discussion.
But ABSOLUTELY the DCR depends on cam timing! And DCR is the only meaningful compression ratio. Detonation happens due to the DCR, nothing to do with SCR or just CR as you have defined. Unless, of course, they work out to be the same. BMEP will not tell you if you need premium to avoid detonation, DCR will. And that was the point of this discussion.
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Joined: Sep 2006
Posts: 1,678
From: Beautiful Pacific NW
Re: E3 spark plugs, will you save gas?
I think its 12:1 from the stuff I've seen. I think this is because its an atkinson cycle. From what I understand its the ratio of the volume of the cylinder with the piston retracted over the volume with it extended. Now in a standard Otto engine cycle, the fuel is injected with the piston retracted the valves are closed and the fuel air mixture is compressed 12x. That requires high octane fuel or the mixture will ingnite before the stroke is complete due to heat from compression.
HOWEVER... the FEH atkinson cycle pops the valves OPEN during part of the compression cycle. This is how they use a standard Otto engine linkage and still have a longer power stroke than a compression stroke. IN this case the fuel air mixture IS NOT compressed 12x. Some of it is pushed back into the manifold from what I've read and the presssure in the cylinder will not increase during that part of the stroke... lower pressure, less heat, no pre-ignition... no need for high octane fuel.
The advantage if I understand things correctly is that you get the full energy of the power stoke out and waste less of the energy compressing the fuel on the compression stroke more than is necessary. With less compression I guess you get a lot less of an OOMPH during the explosion so that might explain the lower torque at low RPM.
Now... I'm an electrical engineer.... I'm not an ICE expert. All info herein is from what I've read online, from asking my brothers and this forum. If there is an ICE expert out there that can fix any errors... I'll take no offense.
HOWEVER... the FEH atkinson cycle pops the valves OPEN during part of the compression cycle. This is how they use a standard Otto engine linkage and still have a longer power stroke than a compression stroke. IN this case the fuel air mixture IS NOT compressed 12x. Some of it is pushed back into the manifold from what I've read and the presssure in the cylinder will not increase during that part of the stroke... lower pressure, less heat, no pre-ignition... no need for high octane fuel.
The advantage if I understand things correctly is that you get the full energy of the power stoke out and waste less of the energy compressing the fuel on the compression stroke more than is necessary. With less compression I guess you get a lot less of an OOMPH during the explosion so that might explain the lower torque at low RPM.
Now... I'm an electrical engineer.... I'm not an ICE expert. All info herein is from what I've read online, from asking my brothers and this forum. If there is an ICE expert out there that can fix any errors... I'll take no offense.
Due to the more complete BURN of the A/F mixture during the power stroke an Atkinson cycle engine can barely keep the catalyst up to operational temperature let alone run a turbocharger.
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Joined: Sep 2006
Posts: 1,678
From: Beautiful Pacific NW
Re: E3 spark plugs, will you save gas?
Wrong, compression ratio has always been maximum volume/ minimum volume. Our ICE has a compression ratio of approximately 12.7 to 1. This would normally cause to much compression and would result in preignition (pinging) but they hold the intake valve open MUCH longer to allow a large percentage of the intake charge to renter the intake to reduce the compression not the compression ratio. This results in a longer burn time and a large delta volume (like a diesel) To under stand this concept you must understand that gasoline has a much larger expansion rate than most ICEs can efficiently use. This is why allot of the fuel is turned into unused heat. If one could give the gasoline a larger delta volume more of the energy would be used to generate power. (again like a diesel) BTW this might be the reason E30 seems to work out the same as pure gasoline.
This results in about 15% better fuel burn BUT lower horsepower esp at low rpm because of the reversion back into the intake disrupts the air flow.
This results in about 15% better fuel burn BUT lower horsepower esp at low rpm because of the reversion back into the intake disrupts the air flow.
For anything other than a 4 cylinder engine, or multiples thereof, this would be true. With 4 cylinders when the intake charge is being forced back out by the upward movement of the pistion the "opposite" piston is on an intake cycle thereby creating the extra "room" and suction for the aforementioned outflow.
With any other than a 4 cylinder (or...) you would need to use some sort of reed flap valve, commonly used in 2 cycle engines, to prevent reverse flow through the throttle body/intake.
The reduction in power/performance is due strictly to the fact that a 2.3L Atkinson cycle engine only has the "lungs" of a 1.6L engine. You gain some of that back as a result of the lowered pumping losses, "virtual" 10:1 compression ratio and thereby a more effective "burn" of the A/F mixture.
Even so the resulting power loss would not be acceptable to the owners were it not for the "makeup" provided by the AC electric motors.
Last edited by wwest; Jan 8, 2008 at 11:48 PM.
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Joined: Sep 2006
Posts: 1,678
From: Beautiful Pacific NW
Re: E3 spark plugs, will you save gas?
At: http://www.fordvehicles.com/suvs/escape/features/specs/
The plain I4 Escape has a 9.7:1 compression ratio.
The plain V6 Escape has a 10:1 compression ratio.
The FEH has a 12.3:1 compression ratio.
But an "effective", useful, compression ratio of only 9.7:1.
The FEH is an extra "low compression" engine.
The FEH does not knock under heavy acceleration with 85 octane,
Probably because shortly after you fuel with 85 octane the engine ECU "learns" that in order to prevent knock/ping when under "load" it enriches the mixture. It would also tend to spend less time in O/D than otherwise and the downshift schedule/mapping would be revised to prevent knock/ping due to lugging.
which is what I use whenever I can find it, and I use it at sea level sometimes.
( I fill up in the Mtns. and drive to Los Angeles, for Example )
Additional Info:
While the physical dimentions of the FEH may indicate a 12.3:1 ratio, due to the Atkinsen valve timing, the actual compression realized is something lower.
The plain I4 Escape has a 9.7:1 compression ratio.
The plain V6 Escape has a 10:1 compression ratio.
The FEH has a 12.3:1 compression ratio.
But an "effective", useful, compression ratio of only 9.7:1.
The FEH is an extra "low compression" engine.
The FEH does not knock under heavy acceleration with 85 octane,
Probably because shortly after you fuel with 85 octane the engine ECU "learns" that in order to prevent knock/ping when under "load" it enriches the mixture. It would also tend to spend less time in O/D than otherwise and the downshift schedule/mapping would be revised to prevent knock/ping due to lugging.
which is what I use whenever I can find it, and I use it at sea level sometimes.
( I fill up in the Mtns. and drive to Los Angeles, for Example )
Additional Info:
While the physical dimentions of the FEH may indicate a 12.3:1 ratio, due to the Atkinsen valve timing, the actual compression realized is something lower.
Ridiculously Active Enthusiast
Joined: Sep 2006
Posts: 1,678
From: Beautiful Pacific NW
Re: E3 spark plugs, will you save gas?
Back in the days of ignition systems using a single coil with distributor, points and condensor, having the most optimal spark plug and spark plug gap was an absolute necessity.
Nowadays with a coil/plug and solid state CD ignition systems almost any modern spark plug will remain fully operational beyond 100,000 miles.
K&N
It costs us $250,000 to rent a Porsche GT3 for running the 24 hours of Daytona and we tyically run a K&N filter for best performance. Those engines will be torn down and rebuilt immeduately after the race.
During the race the throttle will be WIDE open a lot more of the time yours would likely be in a whole year.
Remember that in the normal case your throttle valve will be the major restriction to intake airflow.
Nowadays with a coil/plug and solid state CD ignition systems almost any modern spark plug will remain fully operational beyond 100,000 miles.
K&N
It costs us $250,000 to rent a Porsche GT3 for running the 24 hours of Daytona and we tyically run a K&N filter for best performance. Those engines will be torn down and rebuilt immeduately after the race.
During the race the throttle will be WIDE open a lot more of the time yours would likely be in a whole year.
Remember that in the normal case your throttle valve will be the major restriction to intake airflow.
2008 Escape Hybrid Owner
Joined: Mar 2007
Posts: 280
From: San Diego, California, USA
Re: E3 spark plugs, will you save gas?
So is Compression measured in PSI or PSIG?
Wikipedia says "The compression ratio is a single number that can be used to predict the performance of any engine". A bold statement when there are other engine parameters that are evem more important, ie. displacement.
Wikipedia says "The compression ratio is a single number that can be used to predict the performance of any engine". A bold statement when there are other engine parameters that are evem more important, ie. displacement.
Last edited by DavidH; Jan 9, 2008 at 03:42 AM. Reason: typo
