This is a continuation of various posts, but I thought others might find interesting.
I put together a spread sheet model based on the sheet prepared by J.D. Estill and the Bob Dick intercooler test, feedback and discussion welcome. I do not claim that this sheet is going to give an accurate assessment of performance per say, but should help with modification assessment and help broaden some understanding of what is taking place, especially if others try it out, identify any bugs, or also come up with improvements. Nothing really new here, just a consolidation of information and tools.
The model takes advantage of some simple VB code using empirical methods developed by Crane in the Crane tech pub 410 for calculating mass flow and pressure drop. It also takes advantage of the excel goal seek function combined with some code to iterate through flow conditions to arrive at turbo exit pressure and temperature, and manifold pressure and temperature. A simple pressure drop calculation for a single exhaust pipe minus a muffler or containing a straight thru muffler is at the bottom of the sheet. The calculations rely on an accurate knowledge of volumetric efficiency, BSFC, and ideal AFR. I don’t have the experience to know what the best numbers are, and these numbers will change depending on a particular setup.
From the intercooler test I tried to piece together some information in order to have values for the heat exchanger U value and the mass flow through the cooling air side. Measured ambient conditions were not given in the test, and the intercooler does not operate under steady state conditions, so values that I came up with are rough estimates at best. The purpose of developing them was so that comparisons can be made when other variables are changed. The values are somewhat conservative in that I used the peak intercooler exit temperature conditions to calculate the U value and cooling mass flow. I have only experimented with the dut neck stock intercooler, so feedback from other users welcome who try out the other intercooler numbers. Values to plug in are included in a table on the sheet.
I have a section that does some very basic methanol evaluations. The spreadsheet assumes a pre-intercooler injection point manly because it makes the calculation simpler for cooling effects. The air exiting the compressor is hot enough to vaporize all of the methanol. I only used the latent heat of vaporization, I did not take into account the sensible heat since this would be very small, and the sheet is not that exacting to begin with. The calculation also assumes full vaporization, I don’t think you would get that post intercooler. The thing I don’t know is would you get condensation in the intercooler once you cool to the saturation point now limiting the air/meth stream cooling due to the reverse effect of the latent heat. I have also included a methanol saturation temperature based on pressure. I pulled this info off the net to make the formula, so hopefully it is accurate. I don’t know how to estimate the evaporative effects if you inject just before the TB. Your temp is well below the saturation temps from what I can tell, unless somebody has hard data to say otherwise, and at the high velocity you will be carrying over a high percentage of droplets to the cylinders. This is not a bad thing because it will evaporate in the cylinder during compression and reduce pumping losses by cooling the charge, and will still have detonation reducing effects. I just have no idea how to begin trying to calculate those effects, but the real world tells us they are beneficial.
Like mentioned in the beginning, any experienced experts please dig in and give some critical feedback. The thing I like about this hobby is trying to understand and predict the performance of the car, I hope others get some use out the tool and can help make it better.
I put together a spread sheet model based on the sheet prepared by J.D. Estill and the Bob Dick intercooler test, feedback and discussion welcome. I do not claim that this sheet is going to give an accurate assessment of performance per say, but should help with modification assessment and help broaden some understanding of what is taking place, especially if others try it out, identify any bugs, or also come up with improvements. Nothing really new here, just a consolidation of information and tools.
The model takes advantage of some simple VB code using empirical methods developed by Crane in the Crane tech pub 410 for calculating mass flow and pressure drop. It also takes advantage of the excel goal seek function combined with some code to iterate through flow conditions to arrive at turbo exit pressure and temperature, and manifold pressure and temperature. A simple pressure drop calculation for a single exhaust pipe minus a muffler or containing a straight thru muffler is at the bottom of the sheet. The calculations rely on an accurate knowledge of volumetric efficiency, BSFC, and ideal AFR. I don’t have the experience to know what the best numbers are, and these numbers will change depending on a particular setup.
From the intercooler test I tried to piece together some information in order to have values for the heat exchanger U value and the mass flow through the cooling air side. Measured ambient conditions were not given in the test, and the intercooler does not operate under steady state conditions, so values that I came up with are rough estimates at best. The purpose of developing them was so that comparisons can be made when other variables are changed. The values are somewhat conservative in that I used the peak intercooler exit temperature conditions to calculate the U value and cooling mass flow. I have only experimented with the dut neck stock intercooler, so feedback from other users welcome who try out the other intercooler numbers. Values to plug in are included in a table on the sheet.
I have a section that does some very basic methanol evaluations. The spreadsheet assumes a pre-intercooler injection point manly because it makes the calculation simpler for cooling effects. The air exiting the compressor is hot enough to vaporize all of the methanol. I only used the latent heat of vaporization, I did not take into account the sensible heat since this would be very small, and the sheet is not that exacting to begin with. The calculation also assumes full vaporization, I don’t think you would get that post intercooler. The thing I don’t know is would you get condensation in the intercooler once you cool to the saturation point now limiting the air/meth stream cooling due to the reverse effect of the latent heat. I have also included a methanol saturation temperature based on pressure. I pulled this info off the net to make the formula, so hopefully it is accurate. I don’t know how to estimate the evaporative effects if you inject just before the TB. Your temp is well below the saturation temps from what I can tell, unless somebody has hard data to say otherwise, and at the high velocity you will be carrying over a high percentage of droplets to the cylinders. This is not a bad thing because it will evaporate in the cylinder during compression and reduce pumping losses by cooling the charge, and will still have detonation reducing effects. I just have no idea how to begin trying to calculate those effects, but the real world tells us they are beneficial.
Like mentioned in the beginning, any experienced experts please dig in and give some critical feedback. The thing I like about this hobby is trying to understand and predict the performance of the car, I hope others get some use out the tool and can help make it better.
