D
dangnm
Guest
There is an old motorhead rule that goes something like this
"Never run lean or yer gunna burn a hole in yer pistons"
To avoid confusion, when referrig to this post, the definition of LEAN will be considered A/F greater than stoich and RICH will be considered less than stoich
In the application I'm working on a lean burn with max lambda of 1.1 would be very advantageous however before breaking this rule I want to ensure that I understand the problem entirely.
Emissions aside, With instrumentation of a N/A engine I have found the following.
While running rich:
Power increases as A/F in decreased until roughly 13.5:1 (.9 Lambda)
Exhaust temperatures decrease
From A/F of 13.5 to 14.7 the amount of ignition timing that could be added without detonation did not change.
Increasing intake air temperature requires retardation to prevent detonation
While running lean:
Power decreased
Exhaust temperatures ???? <-- (no instrumentation at time)
Ignition timing required retardation to prevent detonation.
Increasing intake air temperature requires retardation to prevent detonation
From this testing I believed that the motorhead rule evolved due to the following two reasons.
1) Decreased resistance to knock may result in detonation causing engine damage.
2) Motorhead carburated systems typically run rich .8-.9 lambda to take advantage of the power gains running leaner causes EGT's to increase which may lead some to believe that if you go too lean you will "melt the pistons"
I have read the following which seems to be a reasonable explanation of change in knock resistance.
A lean air/fuel mixture burns with most efficiency, so much that the insulating boundary layer also gets consumed and the flame front touches the metal walls. At those locations, there is a dramatic rise in temperature, high enough to cause subsequent charges of air and fuel to spontaneously ignite.
Question 1: is this explanation of the decreased knock resitance correct
Question 2: If detonation and EGT's are controlled will damage still occur.
Question 3: What is the chemical/thermodynamic reason for the increase of power when running with enrichment?
On the surface one would expect that the complete combustion of a stoichiometric fuel/air ratio would produce the maximum power.
"Never run lean or yer gunna burn a hole in yer pistons"
To avoid confusion, when referrig to this post, the definition of LEAN will be considered A/F greater than stoich and RICH will be considered less than stoich
In the application I'm working on a lean burn with max lambda of 1.1 would be very advantageous however before breaking this rule I want to ensure that I understand the problem entirely.
Emissions aside, With instrumentation of a N/A engine I have found the following.
While running rich:
Power increases as A/F in decreased until roughly 13.5:1 (.9 Lambda)
Exhaust temperatures decrease
From A/F of 13.5 to 14.7 the amount of ignition timing that could be added without detonation did not change.
Increasing intake air temperature requires retardation to prevent detonation
While running lean:
Power decreased
Exhaust temperatures ???? <-- (no instrumentation at time)
Ignition timing required retardation to prevent detonation.
Increasing intake air temperature requires retardation to prevent detonation
From this testing I believed that the motorhead rule evolved due to the following two reasons.
1) Decreased resistance to knock may result in detonation causing engine damage.
2) Motorhead carburated systems typically run rich .8-.9 lambda to take advantage of the power gains running leaner causes EGT's to increase which may lead some to believe that if you go too lean you will "melt the pistons"
I have read the following which seems to be a reasonable explanation of change in knock resistance.
A lean air/fuel mixture burns with most efficiency, so much that the insulating boundary layer also gets consumed and the flame front touches the metal walls. At those locations, there is a dramatic rise in temperature, high enough to cause subsequent charges of air and fuel to spontaneously ignite.
Question 1: is this explanation of the decreased knock resitance correct
Question 2: If detonation and EGT's are controlled will damage still occur.
Question 3: What is the chemical/thermodynamic reason for the increase of power when running with enrichment?
On the surface one would expect that the complete combustion of a stoichiometric fuel/air ratio would produce the maximum power.