Hi,

Generally, the p-theta data we get is the one averaged over a few cycles for a particular cylinder. There will be some variation from cylinder to cylinder. Hence it will be okay to take the average of the p-theta data from individual cylinders. This will be more accurate if the data is acquired simultaneously from all cylinders (of course this requires a costly experimental setup). If not, you can take the average of multiple data sets from individual cylinders (e.g. 3 each from cylinders 1, 2 and 3) maintaining the operating conditions constant throughout the trial.

Depends on how you want to present the data. If you want to present the data for each cylinder separately, record few cycles and take a average of the same for individual cylinders.

If you want to present it as a whole for that particular engine (normally done this way), then take the average of each cylinder and then take the average of all the three cylinders' pressure value for the corresponding Crank angle values.