Discussion
There's been a lot of discussion lately on this forum about engines running lean and destroying themselves.
I've been concerned about my engine which is in the high horsepower range and I am using -6 fuel lines.
However, since my engine is fuel injected, and fuel pressure is over 40 pounds, I'm not concerned for the following reasons.
At 40 pounds pressure, and having twin lines feeding the pump,(one from each tank) I think that is far more fuel available than the engine can consume.
Now, let me really add something to this discussion.
What I'm going to talk about applies to all engines, but in this case, I'm only going to refer to normally aspirated engines (non supercharged, or turbo charged) to keep it simple.
I believe a lean mixture will not harm an engine, but detonation will.
Any experienced pilot of a complex aircraft (usually one with fuel injection and constant speed prop) has had to study this in order to get their pilot's license.
An aircraft engine is usually working at a level of output equal to the amount of oxygen available.
At sea level, this is 100% possible rated h.p.. At about 6000 feet, you're down to about 75% power depending on the efficiency of your engine. All aircraft have charts showing your power and fuel burn at various altitudes, manifold pressure, and rpm settings.
All aircraft have some sort of leaning device to compensate for the lack of oxygen as the plane gains altitude. If this was not possible, the mixture would get richer as the plane climbs due to the thinning air.
For years the method of leaning the correct amount was by watching the Exhaust Gas Temperature gauge (EGT) which was usually a single probe in what was determined to be the hottest header. You would lean to maximum temp, then richen back to about 25' of temperature. That is called running rich of peak.
You could also use your ears, and keep leaning until the engine sounded a little rough, then richen till the roughness went away.
Most aircraft now are using a monitor that will show at one time all the cylinder head temps (cht) and egt's of each cylinder using electronic graphs. I mention this because this has been a valuable method of showing the results of leaning.
The efficient use of fuel in an aircraft is very important for the obvious reasons, and for years everyone basically burned more fuel than they had to just to be on "the safe side". However, within the last ten years or so, the two major aircraft engine suppliers has given pilots the option to start leaning on the lean side of peak, claiming you WILL NOT harm the engine, and you can extend your range with only a slight loss of speed and power.
I have to say that I agree, and am sort of a testiment to the fact that it works. I've done 12 Atlantic crossings in my single engine Mooney, and ferried numerous other single engine aircraft across the pond, some as far away as Egypt from the U.S. using this method.
This is the reasoning.
Let's say for example that your ideal mixture is 15/1 for cruising. An ideal max power might be 12/1, and max leaning for range is 18/1. This is what the engine monitor will show. At 12/1, your cylinder head temp might be higher because the engine is working harder, but the egt will be cooler because the fuel is not burning efficiently and is also acting as a coolant. At 15/1 your cht will be high because your combustion is at the best ratio and will burn the hottest, therefore your egt will be high also.
At 18/1, your cht will be lower, as will be your egt, because it is not burning at the most efficient ratio.
Therefore, how can you burn a piston, or overheat an engine if by leaning the mixture, the flame is not hot enough to create that amount of heat.
That's the reason for my previous statement, that knocking, or pre-ignition is the only thing that will really destroy an engine quickly.
I believe a knock sensor that retards the ignition will help save alot of engines.
Feel free to jump in with your comments.
Regards
Jack
I've been concerned about my engine which is in the high horsepower range and I am using -6 fuel lines.
However, since my engine is fuel injected, and fuel pressure is over 40 pounds, I'm not concerned for the following reasons.
At 40 pounds pressure, and having twin lines feeding the pump,(one from each tank) I think that is far more fuel available than the engine can consume.
Now, let me really add something to this discussion.
What I'm going to talk about applies to all engines, but in this case, I'm only going to refer to normally aspirated engines (non supercharged, or turbo charged) to keep it simple.
I believe a lean mixture will not harm an engine, but detonation will.
Any experienced pilot of a complex aircraft (usually one with fuel injection and constant speed prop) has had to study this in order to get their pilot's license.
An aircraft engine is usually working at a level of output equal to the amount of oxygen available.
At sea level, this is 100% possible rated h.p.. At about 6000 feet, you're down to about 75% power depending on the efficiency of your engine. All aircraft have charts showing your power and fuel burn at various altitudes, manifold pressure, and rpm settings.
All aircraft have some sort of leaning device to compensate for the lack of oxygen as the plane gains altitude. If this was not possible, the mixture would get richer as the plane climbs due to the thinning air.
For years the method of leaning the correct amount was by watching the Exhaust Gas Temperature gauge (EGT) which was usually a single probe in what was determined to be the hottest header. You would lean to maximum temp, then richen back to about 25' of temperature. That is called running rich of peak.
You could also use your ears, and keep leaning until the engine sounded a little rough, then richen till the roughness went away.
Most aircraft now are using a monitor that will show at one time all the cylinder head temps (cht) and egt's of each cylinder using electronic graphs. I mention this because this has been a valuable method of showing the results of leaning.
The efficient use of fuel in an aircraft is very important for the obvious reasons, and for years everyone basically burned more fuel than they had to just to be on "the safe side". However, within the last ten years or so, the two major aircraft engine suppliers has given pilots the option to start leaning on the lean side of peak, claiming you WILL NOT harm the engine, and you can extend your range with only a slight loss of speed and power.
I have to say that I agree, and am sort of a testiment to the fact that it works. I've done 12 Atlantic crossings in my single engine Mooney, and ferried numerous other single engine aircraft across the pond, some as far away as Egypt from the U.S. using this method.
This is the reasoning.
Let's say for example that your ideal mixture is 15/1 for cruising. An ideal max power might be 12/1, and max leaning for range is 18/1. This is what the engine monitor will show. At 12/1, your cylinder head temp might be higher because the engine is working harder, but the egt will be cooler because the fuel is not burning efficiently and is also acting as a coolant. At 15/1 your cht will be high because your combustion is at the best ratio and will burn the hottest, therefore your egt will be high also.
At 18/1, your cht will be lower, as will be your egt, because it is not burning at the most efficient ratio.
Therefore, how can you burn a piston, or overheat an engine if by leaning the mixture, the flame is not hot enough to create that amount of heat.
That's the reason for my previous statement, that knocking, or pre-ignition is the only thing that will really destroy an engine quickly.
I believe a knock sensor that retards the ignition will help save alot of engines.
Feel free to jump in with your comments.
Regards
Jack
knock sensors are notouriously difficult things to setup properly on modified engines, and are only really effective at low engine speeds as they have a hard time picking out the knocking from all the other noises at WoT.
A restriction in the fuel supply leading to an over lean mixture at high engine rpm may well lead to severe detonation and subsequent damage before a knock sensing rig will come into effect.
There are some other strategies - wide band lambda sensors, ion sensors and even exhaust gas temps can be used by a decent ecu to adjust fuelling as required.
For a fuel injected setup you need to make sure that your pumps, fuel lines, etc will supply all the injectors at a 100% duty cycle + a significant safety margin.
I've had problems on my current car with reaching the limits of the feed pumps in the fuel tank.
>> Edited by Miraz on Monday 13th January 08:05
A restriction in the fuel supply leading to an over lean mixture at high engine rpm may well lead to severe detonation and subsequent damage before a knock sensing rig will come into effect.
There are some other strategies - wide band lambda sensors, ion sensors and even exhaust gas temps can be used by a decent ecu to adjust fuelling as required.
For a fuel injected setup you need to make sure that your pumps, fuel lines, etc will supply all the injectors at a 100% duty cycle + a significant safety margin.
I've had problems on my current car with reaching the limits of the feed pumps in the fuel tank.
>> Edited by Miraz on Monday 13th January 08:05
Jack,
From what I can tell from your posting, you've just contradicted yourself. You started by saying that pilots use a fairly seat of the pants method of figuring out the correct fuel mixture, and the theory has always been to err on the side of running too rich, just to be on the safe side. Then a couple of aircraft manufacturers have come up with advice that says that you can run a bit leaner than you have been. That doesn't mean that you can run a lean mixture, just that you don't have to run it as rich as you used to.
If you're running fuel injection, and you have a fuel pressure sensor (which I guess you do), and the pressure in your fuel rail is 40psi, then you aren't going to have a problem with running lean (assuming your fuel injection is set up to deliver the correct dose of fuel on each pulse). However, if you noticed the fuel pressure dropping significantly below 40psi, would you feel confident to keep on driving, or would you pull over and stop? I know what I would do.
James
From what I can tell from your posting, you've just contradicted yourself. You started by saying that pilots use a fairly seat of the pants method of figuring out the correct fuel mixture, and the theory has always been to err on the side of running too rich, just to be on the safe side. Then a couple of aircraft manufacturers have come up with advice that says that you can run a bit leaner than you have been. That doesn't mean that you can run a lean mixture, just that you don't have to run it as rich as you used to.
If you're running fuel injection, and you have a fuel pressure sensor (which I guess you do), and the pressure in your fuel rail is 40psi, then you aren't going to have a problem with running lean (assuming your fuel injection is set up to deliver the correct dose of fuel on each pulse). However, if you noticed the fuel pressure dropping significantly below 40psi, would you feel confident to keep on driving, or would you pull over and stop? I know what I would do.
James
James.
Good points, but it wasn't so much a matter of contradicting myself, but the fact that as monitoring technology changed, it allowed pilots to adjust fuel more precisely. It also basically removed the myth that running lean would be harmful to the engine.
The biggest problem that aircraft engines have is an uneven distribution of air to each cylinder because of intake manifold design (moreso than automotive engines) which compounds the problem due to the fact that normally each fuel nozzle is the same size. EFI systems have not yet reached production aircraft which use a servo that senses air flow, then meters fuel to a spider (distribution block) that has a fuel line running from it to each nozzle which is located in the cylinder head just before the intake valve. A company the last few years will size fuel injector nozzles for you based on results you send them determined by in flight tests. To do this test, you have to have one of these graphic engine monitors, and a digital fuel flow meter. You fly level, and keep leaning back at intervals until the engine almost stops, or you can't take the roughness any more. You have to write down all cylinder head temps,rpm drop, and egt's for each change, then their computer will determine the correct size injector so that each cylinder will run at the same temperature, not necessarily the same power output.
Even a car with EFI is only monitoring the exhaust temp from the combination of four cylinders, and using that data in combination from other sources to pulse the injectors.
One time when I had the Cobra on a driveline dyno, we actually gained power at full throttle by dropping the fuel pressure from 50 lbs to 38 lbs. Better fuel to air ratio.
If I was driving along and the fuel pressure started dropping, I believe at this time with my way of thinking and there was somewhere I had to get to (hot date), I'd just keep driving unless the roughness became so bad, I felt the vibration might damage the car.
I realize that we're talking about two different type of engines that operate in two different enviroments, but I believe the same combustion principles apply.
I've wondered if running lean would cause detonation. It would be interesting to see some data on that.
Just a little more fuel for thought!!
Jack
>> Edited by USCANAM on Monday 13th January 13:16
Good points, but it wasn't so much a matter of contradicting myself, but the fact that as monitoring technology changed, it allowed pilots to adjust fuel more precisely. It also basically removed the myth that running lean would be harmful to the engine.
The biggest problem that aircraft engines have is an uneven distribution of air to each cylinder because of intake manifold design (moreso than automotive engines) which compounds the problem due to the fact that normally each fuel nozzle is the same size. EFI systems have not yet reached production aircraft which use a servo that senses air flow, then meters fuel to a spider (distribution block) that has a fuel line running from it to each nozzle which is located in the cylinder head just before the intake valve. A company the last few years will size fuel injector nozzles for you based on results you send them determined by in flight tests. To do this test, you have to have one of these graphic engine monitors, and a digital fuel flow meter. You fly level, and keep leaning back at intervals until the engine almost stops, or you can't take the roughness any more. You have to write down all cylinder head temps,rpm drop, and egt's for each change, then their computer will determine the correct size injector so that each cylinder will run at the same temperature, not necessarily the same power output.
Even a car with EFI is only monitoring the exhaust temp from the combination of four cylinders, and using that data in combination from other sources to pulse the injectors.
One time when I had the Cobra on a driveline dyno, we actually gained power at full throttle by dropping the fuel pressure from 50 lbs to 38 lbs. Better fuel to air ratio.
If I was driving along and the fuel pressure started dropping, I believe at this time with my way of thinking and there was somewhere I had to get to (hot date), I'd just keep driving unless the roughness became so bad, I felt the vibration might damage the car.
I realize that we're talking about two different type of engines that operate in two different enviroments, but I believe the same combustion principles apply.
I've wondered if running lean would cause detonation. It would be interesting to see some data on that.
Just a little more fuel for thought!!
Jack
>> Edited by USCANAM on Monday 13th January 13:16
First, I just want to thank Stig for posting Ultima's response to fueling requirements and fuel line size. Ted's been doing this for a while now, and I've spoken to him in the past about a few blown motors on his demo cars. Good engine builders know what kills their motors, and for us novices a good look at the plugs will get you off on the right start. I've not experienced inadequate fueling on my little 530hp powered Ultima with the AN6 size hose.
I think the general concensus of this forum has been to equate inadequate fuel with burned pistons and valves. To tell you the truth, though, I'm more concerned with improper timing of spark and fuel than I am running too lean. The timing on chevy's are often over advanced. In my experience, detonation and preignition is what really hurts a motor. In fact, a quick search on preignition brought up a few interesting articles that explains this better than I can
www.streetrodstuff.com/Articles/September_2000/Engine_Basics_I.php
www.aera.org/Members/EngineTech/engine.htm
In my case, running too rich or too lean, is very easily identified with my stack injection. If its too rich, then you hear "popping" out the exhaust, if its too lean, then you hear a "crackling" or "popping" through the stacks. Its really pretty easy to listen for, though, a little embarressing when experienced in public!
Actually kind of fun until the neighborhood banned me from testing so close to home ;(
I'm sure the Amerispeed motors have the timing preset, but the timing needs to be checked (like most things) every once in a while. Also, you need to pay special attention to the spark plugs and octane fuel your using. I don't know what your situation in the UK is like, but watered down bad gas (petrol) does get sold here. Most of the guys who are serious about checking their timing, don't just check it at idle but they check it at 3500rpm. I think as long as you know what to listen for, and you can read spark plugs at a basic level, then you should be fine. I just don't see poor fueling being a main concern for most people.
Cheers!
-Mack
I think the general concensus of this forum has been to equate inadequate fuel with burned pistons and valves. To tell you the truth, though, I'm more concerned with improper timing of spark and fuel than I am running too lean. The timing on chevy's are often over advanced. In my experience, detonation and preignition is what really hurts a motor. In fact, a quick search on preignition brought up a few interesting articles that explains this better than I can
www.streetrodstuff.com/Articles/September_2000/Engine_Basics_I.php
www.aera.org/Members/EngineTech/engine.htm
In my case, running too rich or too lean, is very easily identified with my stack injection. If its too rich, then you hear "popping" out the exhaust, if its too lean, then you hear a "crackling" or "popping" through the stacks. Its really pretty easy to listen for, though, a little embarressing when experienced in public!
Actually kind of fun until the neighborhood banned me from testing so close to home ;( I'm sure the Amerispeed motors have the timing preset, but the timing needs to be checked (like most things) every once in a while. Also, you need to pay special attention to the spark plugs and octane fuel your using. I don't know what your situation in the UK is like, but watered down bad gas (petrol) does get sold here. Most of the guys who are serious about checking their timing, don't just check it at idle but they check it at 3500rpm. I think as long as you know what to listen for, and you can read spark plugs at a basic level, then you should be fine. I just don't see poor fueling being a main concern for most people.
Cheers!
-Mack
Strange isn't it? You know who the guy to talk to about these issues? Grumpyvette over at www.chevytalk.com performance forum. He's a pretty smart dude...
Cheers!
-Mack
Cheers!
-Mack
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