17-07-2015, 02:26 PM
Having done a lot of research I am wondering if anyone has ever looked into the effects of the engine temperature on diesel knock. Diesels work best when the cylinders are hot. This means that the diesel vaporises really easily and starts combustion easily. Having a colder cylinder means that the diesel doesn't vaporise as easily and forms lots of little blobs of diesel.
These blobs ignite in a much more fierce and uncontrolled way compared to how diesel should burn which is a smooth burn which spreads outwards evenly.
Looking at mine it rarely gets about 70ish *c. This would mean that the cylinder walls are a lot cooler than they should be so would cause these small blobs to exist. Also when engine temps are colder the injector moves earlier in the cycle. This basically is to compensate for how much longer it takes the diesel to ignite from these blobs rather than a fine mist and vapour.
It may not get rid of the physical injector rattle noise but may help with diesel knock if I am to make the engine run at the correct operating temperature of around 86c-90c which is what the gauge shows and also most thermostats are supposed to begin to open at 86c.
Another possibility is that the temperature sensors on these cars are rubbish. This would be the worse issue to have as if the temperatures are reading low the injection timing would move further forwards in the cycle even though the cylinders are reaching a good temperature. If this is the case then the explosion will occur quickly like it should but too far forwards in the cycle of the engine.
I am not really sure how much of a difference it would make in the real world but I am damn tempted to give it a go and see if I can make my HDI run at its correct temperature which I am convinced should still be higher than what it currently sits at now.
These blobs ignite in a much more fierce and uncontrolled way compared to how diesel should burn which is a smooth burn which spreads outwards evenly.
Looking at mine it rarely gets about 70ish *c. This would mean that the cylinder walls are a lot cooler than they should be so would cause these small blobs to exist. Also when engine temps are colder the injector moves earlier in the cycle. This basically is to compensate for how much longer it takes the diesel to ignite from these blobs rather than a fine mist and vapour.
It may not get rid of the physical injector rattle noise but may help with diesel knock if I am to make the engine run at the correct operating temperature of around 86c-90c which is what the gauge shows and also most thermostats are supposed to begin to open at 86c.
Another possibility is that the temperature sensors on these cars are rubbish. This would be the worse issue to have as if the temperatures are reading low the injection timing would move further forwards in the cycle even though the cylinders are reaching a good temperature. If this is the case then the explosion will occur quickly like it should but too far forwards in the cycle of the engine.
I am not really sure how much of a difference it would make in the real world but I am damn tempted to give it a go and see if I can make my HDI run at its correct temperature which I am convinced should still be higher than what it currently sits at now.
