Think about this:
Shrinker Total Timing and Poor Vaporization
Its all to do with the species of gasses output from the chamber. You have to look at the percentage of each species to understand why. As a burn progresses the chemicals produced go through stages until the final outcome is for a perfect burn just water and CO2. Our engines don't get to that stage but they get to the stage of producing water and CO and CO2 and a little bit of NOx and having some O2 left over. The point to consider is that it takes time to go through the stages to get to the final result.
The most important stage is the preparation prior to ignition. When that is not right, as in this engine, the flame kernel doesn't grow fast enough and the result is a lower cylinder pressure at an equivalent crank position to a good kernel. The flame kernel is a growth of laminar conditions to around 20mm diameter, then the conditions change to turbulent flame and the speed of burn is much faster. What you have to know is its droplet size and the vaporization that influences the speed of both laminar and turbulent flames. So when an engine has large droplets its needs a lot of heat to vaporize them in the time available.
When I say to you guys that a particular engine hasn't got enough vaporization that is what I'm commenting on. How it looks inside the cylinder is like this, the AFR at ignition time is leaner than the average of the cylinder, lets say the average is 12.8 but at ignition time the AFR around the plug is AFR 14, the flame is going to grow slow and some of the flames energy is going to used in vaporizing the fuel thats not gas yet. So the flame kernel doesn't generate enough heat and you dont get a TAN plug, you also run the risk of extinguishing the flame if turbulence is poorly directed. The kernel uses up about 10% of the mixture then the conditions transition to turbulent. Once the flame is turbulent it cant be extinguished. However the conditions toward the remainder of the chamber ahead of the flame kernel front are still under vaporized, therefor requiring energy from the advancing flame front to vaporize mixture ahead of the front, not an efficient way to go. It's the burn angle duration between 10 and 90% that matters. Good burns are in the range of 15 to 25 degrees. Burns of engine with poor vaporization can be as long as 45 degrees. THAT'S WHY some engines make best power at timings like 38 to 45 degrees compared to another that best at 28 degrees.
The burn time determines the peak cylinder pressure.
