# What data do I need to plot a BSFC map

I have an 4 stroke spark ignition engine simulator which takes user inputs and outputs performance data.

I need rpm, torque and brake specific fuel consumption (bsfc) to plot the bsfc map. I am able to plot torque and bsfc against rpm respectively without any problems.

Since a contour plot requires x(rpm), y(torque) and z(bsfc) where z is a function of x and y, how can I express bsfc in terms of rpm and torque or can I take advantage of the simulator to produce raw data required to plot the map saving me trouble in deriving the equation. If its the latter, how can I obtain bsfc data? What parameters should I change or keep constant?

• Unless you change some other parameter (e.g. throttle position), you'll always get the same bsfc and torque at any given rpm from the simulation (no contour possible). – Dan Apr 27 '15 at 5:04
• Does changing the intake pressure simulates changing the throttle position? – Eugene Apr 27 '15 at 13:11
• That would be similar and should get the variation that you need to produce a contour plot. For a given RPM, throttle position (TP) will vary manifold air pressure (MAP) and that's what'll control power/BSFC. The only difference here is that, for a given TP, MAP will change with RPM. Changing MAP should be close enough for your purposes, I think. I am a little surprised that your simulator doesn't include a throttle. It's a pretty important component of most spark ignition engines. – Dan Apr 27 '15 at 18:04
• OK, that's a start. So I have a multiple curves on the torque and SFC graph for different pressure, then how would I translate them into a contour map? Say I'm plotting torque against rpm from 1000-6000rpm (at increments of 10rpm) with throttle wide open (ambient pressure) this graph would envelope the SFC contour. Since this graph has 500 points, I would need SFC data of 500x500? How would I get it? Plot SFC against rpm from 1000-6000rpm for pressure ranging from 100kpa-50kpa with decrement of 0.1 kpa? How would this then fit into the contour plot? Sorry, I don't know how to plot contour plot – Eugene Apr 27 '15 at 20:14
• yeah... how to contour plot is plot is going to be program specific and you don't seem to have a great handle on what a contour plot is. They show variation of one variable (BSFC,z) in terms of two others (rpm, torque=x,y). You'll have curves in x,y which correspond to constant values of z (like a map showing terrain). Your program is going to need a list of the (x,y,z) points and then it'll generate the plot. It may also be necessary to interpolate onto a uniform grid of x,y. Really, take the time to go and understand contour plots first, then this'll make more sense. – Dan Apr 27 '15 at 20:33