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I was reading about AaronGTR's failed gaskets in his thread in the performance section.
Some members speculate that the failure was due to lean condition. They said the lean condition would result in excessively high combustion pressures, leading to the gasket failure.
This doesn't make sense to me. I'm not arguing, just inquiring.
My understanding: A lean condition will cause problems because it increases the combustion temperatures. Increased temperatures can create hot spots and increase the burn rate: both which can cause pre-ignition and detonation. The main reason excess fuel cools the charge is because it absorbs significant heat as it vaporises and also increases the matter in the chamber. This extra matter requires more heat to change temperature (eg. heat sink).
AaronGTR said no knock was logged during failure, and assuming his sensor is accurate, then being leaner than suggested 11.5 did not cause detonation.
It was then stated that excessive pressure due to a lean condition (not necessarily knock) caused the gasket failure.
I agree that chamber pressure will rise as the mixture approaches stoich. This is mostly due to increasing temps (PV=nRT: this tells us that increasing T increases P), and as I described above, less fuel increases the temp. Pressure will also raise (to a lesser degree) because less O2 is displaced by the excess fuel (O2 is the limiting reagent, more O2 means a greater rxn, means more energy released).
However, the combustion pressure is the force that is being measured on a dyno in tq. There are other members who have recorded higher tq numbers on a dyno (indicating higher combustion pressures) yet their gaskets did not fail. This is why I agree with Aaron; the lean* condition did not cause the failure. I would appreciate any comments, especially pointing out my misunderstandings.
*lean being relative (in this case greater than 11.5)
Some members speculate that the failure was due to lean condition. They said the lean condition would result in excessively high combustion pressures, leading to the gasket failure.
This doesn't make sense to me. I'm not arguing, just inquiring.
My understanding: A lean condition will cause problems because it increases the combustion temperatures. Increased temperatures can create hot spots and increase the burn rate: both which can cause pre-ignition and detonation. The main reason excess fuel cools the charge is because it absorbs significant heat as it vaporises and also increases the matter in the chamber. This extra matter requires more heat to change temperature (eg. heat sink).
AaronGTR said no knock was logged during failure, and assuming his sensor is accurate, then being leaner than suggested 11.5 did not cause detonation.
It was then stated that excessive pressure due to a lean condition (not necessarily knock) caused the gasket failure.
I agree that chamber pressure will rise as the mixture approaches stoich. This is mostly due to increasing temps (PV=nRT: this tells us that increasing T increases P), and as I described above, less fuel increases the temp. Pressure will also raise (to a lesser degree) because less O2 is displaced by the excess fuel (O2 is the limiting reagent, more O2 means a greater rxn, means more energy released).
However, the combustion pressure is the force that is being measured on a dyno in tq. There are other members who have recorded higher tq numbers on a dyno (indicating higher combustion pressures) yet their gaskets did not fail. This is why I agree with Aaron; the lean* condition did not cause the failure. I would appreciate any comments, especially pointing out my misunderstandings.
*lean being relative (in this case greater than 11.5)
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