pressure vs crank angle (p-theta )diagram for a 4 cylinder naturally aspirated diesel

monty37

I want to plot a cylinder pressure vs crankangle diagram for a 4 cylinder naturally aspirated diesle engine ,do I require AVL boost for this ?and how can you plot it manually?

OldEngr63

I need to be sure we are speaking the same language here. When you say "AVL," I hear AV List, a maker of precision instruments in Austria; is that what you mean? If not, please clarify.

It is virtually impossible to get a cylinder pressure - crank angle plot for a running engine by hand. You simply cannot record the data fast enough. For a non-running engine, you could acquire the data on a static basis, point-by-point, but once you reach the firing point, with no fuel the pressures are way off; with fuel the engine begins to run, so you cannot keep up with the data.

Typically the data is acquired on one cylinder only, and the other cylinders are assumed to be similar. If you really want to measure all four cylinders, you are looking at a lot more data acquisition equipment.

Tell me more about what you have in mind, and clear up what you mean by AVL, and maybe we can go further with this.

monty37

Well I meant AVL BOOST (virtual engine simulation tool) was used to plot the pressure vs crank angle .In my case it is a naturally aspirated four cyl diesel engine ,one of my profs told me I dont have to go for AVL i can plot it theoritically..but I felt it would not be possible as there are 4 cylinders involved where pressure has to be plotted

OldEngr63

I am not acquainted with the simulation tool you speak of, so it is a good thing I ask for clarification of that point.

If you know what cylinder pressure is when the valves close, then you can plot the pressure during the compression stroke by simply assuming an adiabatic compression and calculating the necessary pressure points for each crank angle. If you then know the firing pressure, you can assume an adiabatic expansion down to the point where the valves open and thus be able to calculate all of the required points for each crank angle on the power stroke.

The fact that there are four cylinders involved really makes no difference. Ideally, they are all alike, but simply phased differently.

monty37

Well I get your point ,If I know the cylinder pressure and firing pressure at a particular crank angle for each cylinder I can plot pressure vs crank angle .

I also seem to have little idea of AVL as i found it being used in a paper though I could not imagine why was it necesary if this plot was possible theoritically.

Is the plot we get calculating manually approximate?

OldEngr63

Sure, it is approximate to reality. All theoretical curves are approximations to reality. If you make actual measurements, they will deviate slightly. Then, are you seeing reality, or measurement error?