Discussion and questions related to the course Understanding AFR
How can i find the max EGT limit for a particular engine ? what should i consider for EGT limitations?
Exhaust gas temperature or EGT is one of those parameters that is often mentioned but seldom discussed. In particular, the specific EGT will be influenced by both the air-fuel ratio and the ignition advance. we have a webinar 067 which covers this to help you learn the effects of far and ignition timing on the EGT there is plenty of links to what tuners think is the safest EGT but there is so many factors involved to work out for different types of engines such as NA TURBO size of turbines back pressure fuel type etc,
check out the webinar and hopefully, it will give you what your after
Not sure exactly what is concerning you?
In no particular order.
Exhaust valve material - they will weaken at high temperatures and the alloy used will affect their maximum operating temperature. Wider exhaust seats and bronze guides that are correctly clearanced will help pull heat out of the valve.
The exhaust manifold design, material, and build quality - restrictive designs hold the hot gas in them longer which transfers more heat into the manifold and not through the turbine. Again, the material used is important as a higher expansion alloy will expand more and so stress welds and parent material more and increase the probability of cracking at stress risers - careful design can help here. There are some manifolds for sale, some from 'reputable' suppliers, that have poor welding penteration, or wall thicknesses are inadaquate, or have other problems that can cause failure under high loads.
Something that many overlook is the turbo-charger itself - turbine, followed by oil/bearing temperature and turbine housing. Turbine wheels are made of a variety of alloys, even ceramics, and these lose strength, even melt, at excessive EGTs - the reputable manufacturers will have a maximum sustained temperature for EGT and some will have slightly higher temp's for SHORT bursts - there will be a little wiggle room but they should be a good guide. As you will gather, the higher the EGT, the hotter the turbo-charger and this is going to put a lot of heat into bearings and oil - make sure you are using a GOOD quality synthetic with an adaquate supply of CLEAN oil and the drain has plenty of capacity as this will reduce coking and other problems - if practical, if there will be sustained hoigh temperatures, a water cooled bearing may be worth considering. The last thing is the turbine housing as different manufacturersw will use different quality casting and cast iron/stainless steel - some cheap 'chinese' housings may develop cracking over time.
All things being equal, I would probably consider the turbine wheel temperature limit the most critical, assuming the rest isn't significantly compromised.