Andy Blyth Posted August 15, 2011 Share Posted August 15, 2011 With a bit of spare time, I set up a test rig this afternoon to characterise the stock 440cc injectors, as part of my move to a standalone ECU. First up is a measurement of the injector flow at a range of rail pressures from 1.5 bar to 4.5 bar: The measurements were taken by using an adjustable fuel pressure regulator to set the rail pressure with one injector on (the pressure is different with the injector off and on due to the design of the FPR). For each test, the injector was opened for 30 seconds into a 250cc graduated cylinder. The cylinder was marked every 2cc so the best measurement I could take was to the nearest cc. Each reading was doubled to get the flow in cc/min. The next bit took forever! I set up a standalone ECU to open the injector at 50% duty cycle at a frequency of 50 Hz (equal to sequential injection at 6000 RPM) for 40 seconds. This was carefully chosen to maximise the use of the graduated cylinder and to maximise the effect of the injector dead times to improve accuracy. I applied a bit of maths to the volume measured compared to the expected volume in the ideal case (i.e. no dead time) to calculate the dead time. The pressure was varied between 1.5 bar and 4.5 bar again and the voltage was varied between 8V and 15V - this should also account for dead times during cranking. The calulated dead times based on my measurements are as follows: In picture form: As you can see, the graph isn't perfectly smooth. I believe this is due to my measurements only being made to the nearest cc. For some of the "strange" points, I retested to ensure that the result was repeatable. I've given the "raw" measurements so that you can choose to apply some smoothing of the data if you wish. Quote Link to comment Share on other sites More sharing options...
Homer Posted August 15, 2011 Share Posted August 15, 2011 When you say dead time, is this the same as injector lag? Very interesting read, kudos for posting your findings Quote Link to comment Share on other sites More sharing options...
Scott Posted August 15, 2011 Share Posted August 15, 2011 That's all way over my head. However I'm in to find out if someone points out how much fuel the stock injectors can flow in relation to BHP in the 2JZ Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 15, 2011 Author Share Posted August 15, 2011 When you say dead time, is this the same as injector lag? Yes, just different names for the same thing. Basically it's the correction that an ECU has to apply to the command going to an injector to account for the mechanical effects. For example, if you had a rail pressure of 3 bar (compared with intake manifold pressure) and a battery voltage of 14V, the dead time would be 0.58 ms (from above). If the ECU determined that at a particular engine speed and load that it wanted 2 ms worth of fuel, it would have to command the injector to open for 2.58 ms to get the desired fuel quantity. If it only commanded 2 ms, it would only get (2 - 0.58 = 1.42) ms worth of fuel and the mixture would be leaner than expected. Quote Link to comment Share on other sites More sharing options...
Ian C Posted August 15, 2011 Share Posted August 15, 2011 Top work Good to see that 2.5bar (36psi) static pressure pretty much equates to 440cc, that certainly validates the work you've done. Did you notice any significant change in the spray pattern as the pressures increased? I understand that's the biggest risk to ramping up the pressure significantly, the spray distribution goes to pot. Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 16, 2011 Author Share Posted August 16, 2011 That's all way over my head. However I'm in to find out if someone points out how much fuel the stock injectors can flow in relation to BHP in the 2JZ It's possible to do a quick back-of-an-envelope calc for this. Assuming a Brake Specific Fuel Consumption of 0.65 for a intercooled, turbocharged petrol engine we get: 0.65 [lbs/bhp.hr] = 0.295 [kg/bhp.hr] = 0.0492 [kg/bhp.hr] per injector = 8.207 E-4 [kg/bhp.min] per injector = 1.108 E-3 [litres/bhp.min] per injector (assuming density of 0.741 kg/litre from V-power datasheet) = 1.108 [cc/bhp.min] per injector. At 3 bar (standard FPR pressure) you are flowing 465 cc/min, therefore you should be able to support (465/1.108) = 420 bhp. At 4 bar you are flowing 546 cc/min, therefore you should be able to support (546/1.108) = 493 bhp. If you get less conservative and use a BSFC of 0.6, the power figures become 455 bhp and 534 bhp for 3 and 4 bar respectively. Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 16, 2011 Author Share Posted August 16, 2011 Top work Good to see that 2.5bar (36psi) static pressure pretty much equates to 440cc, that certainly validates the work you've done. Did you notice any significant change in the spray pattern as the pressures increased? I understand that's the biggest risk to ramping up the pressure significantly, the spray distribution goes to pot. Yes there was a distinct difference in the spray quality as the pressure was varied. At the lower pressures (1.5 and 2 bar) the flow was mainly in two jets without much "spray." As the pressure reached 3 bar, the jets turned more into a cone of spray with better atomisation. At 4 bar it was even more pronounced - to the extent that I would be tempted to run 4 bar rail pressure before moving to "550 cc" injectors. As a little bit of a play at the end I ramped the pressure to over 6.5 bar and saw a powerful cone of good spray when the injector was held open. When I tested it with a 50% duty cycle, the flow seemed to be much lower than at 3 bar (unfortunately I didn't get any measurements) suggesting that the dead time went through the roof. This would make them a nightmare to control. Quote Link to comment Share on other sites More sharing options...
pedrosixfour Posted August 16, 2011 Share Posted August 16, 2011 You guys really have a way of making a person feel decidedly thick. Top work Andy. (I think!) Quote Link to comment Share on other sites More sharing options...
Scott Posted August 16, 2011 Share Posted August 16, 2011 It's possible to do a quick back-of-an-envelope calc for this. Assuming a Brake Specific Fuel Consumption of 0.65 for a intercooled, turbocharged petrol engine we get: 0.65 [lbs/bhp.hr] = 0.295 [kg/bhp.hr] = 0.0492 [kg/bhp.hr] per injector = 8.207 E-4 [kg/bhp.min] per injector = 1.108 E-3 [litres/bhp.min] per injector (assuming density of 0.741 kg/litre from V-power datasheet) = 1.108 [cc/bhp.min] per injector. At 3 bar (standard FPR pressure) you are flowing 465 cc/min, therefore you should be able to support (465/1.108) = 420 bhp. At 4 bar you are flowing 546 cc/min, therefore you should be able to support (546/1.108) = 493 bhp. If you get less conservative and use a BSFC of 0.6, the power figures become 455 bhp and 534 bhp for 3 and 4 bar respectively. Yes there was a distinct difference in the spray quality as the pressure was varied. At the lower pressures (1.5 and 2 bar) the flow was mainly in two jets without much "spray." As the pressure reached 3 bar, the jets turned more into a cone of spray with better atomisation. At 4 bar it was even more pronounced - to the extent that I would be tempted to run 4 bar rail pressure before moving to "550 cc" injectors. As a little bit of a play at the end I ramped the pressure to over 6.5 bar and saw a powerful cone of good spray when the injector was held open. When I tested it with a 50% duty cycle, the flow seemed to be much lower than at 3 bar (unfortunately I didn't get any measurements) suggesting that the dead time went through the roof. This would make them a nightmare to control. Great information, thanks for the work you put in there. Be very interesting to see a stock fuel setup with aftermarket FPR to see how far the fuel can be taken in the real world. If they can push 450hp then the hybrid route just got a little bit cheaper Quote Link to comment Share on other sites More sharing options...
Ian C Posted August 16, 2011 Share Posted August 16, 2011 Great information, thanks for the work you put in there. Be very interesting to see a stock fuel setup with aftermarket FPR to see how far the fuel can be taken in the real world. If they can push 450hp then the hybrid route just got a little bit cheaper If I'm thinking this through correctly, wouldn't 1.2bar of boost with a 4 bar static pressure = running the injectors at 5.2bar on full boost? So starting to push the dead time issue at higher pressures, and the spray pattern? Quote Link to comment Share on other sites More sharing options...
Scott Posted August 16, 2011 Share Posted August 16, 2011 If I'm thinking this through correctly, wouldn't 1.2bar of boost with a 4 bar static pressure = running the injectors at 5.2bar on full boost? So starting to push the dead time issue at higher pressures, and the spray pattern? I was thinking more 3 bar static though. Hybrids generally only manage around 450hp? Quote Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 16, 2011 Author Share Posted August 16, 2011 If I'm thinking this through correctly, wouldn't 1.2bar of boost with a 4 bar static pressure = running the injectors at 5.2bar on full boost? So starting to push the dead time issue at higher pressures, and the spray pattern? Yes, the fuel rail will be at 5.2 bar which will make the fuel pump work harder - you'd need to check the datasheet of the pump to ensure that it can flow suffiecent fuel at that pressure. The injectors however would have 5.2 bar on the fuel side and 1.2 bar on the air side so they would only "see" 4 bars across them. They would behave the same way as they would say at idle with for example -0.75 bar on the air side and 3.25 bar on the fuel side. There's still 4 bars across the injector. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 18, 2011 Share Posted August 18, 2011 Great info Andy, yet more to add to my folder of stuff! Thanks very much for sharing this. Quote Link to comment Share on other sites More sharing options...
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