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Diesel Tuning Fundamentals: Effect of Fuel Pressure on Engine Performance

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Effect of Fuel Pressure on Engine Performance


00:00 - In this demonstration we're going to have a look at the effect of fuel pressure on the fuel injection pulse width and we're also going to see how the fuel pressure affects the power the engine produces during a full power ramp run.
00:12 So let's get our engine up and running and we'll start by looking at the effect on the injection pulse width.
00:18 We'll start our test here with our engine operating at 2000 RPM.
00:22 And I'm using a reasonable amount of load, we're delivering 60 milligrams of fuel.
00:27 On the right hand side we can see that our injection event is starting 11.7 degrees before TDC.
00:33 We can see that it's finishing 2.5, 2.6 degrees before TDC.
00:38 So our full injection pulse width there, our injection event, is all dealt with before the piston reaches TDC.
00:44 At the bottom here we've also got our injection pressure, our fuel pressure, and we can see at the moment we're sitting at around about 160 megapascals.
00:55 So what we're going to do now is head across to our fuel pressure target table.
00:58 And I've highlighted all of the cells that surround the area we're operating in just so we don't end up with any effects of interpolation.
01:05 What I'm going to do is just reduce the target in all of those cells by 80 megapascals.
01:12 So that's quite a dramatic change in our fuel pressure.
01:15 Let's head back across to our timing table and we'll have a look and see how that's affected our injection timing.
01:22 What we'll do is we'll just pause our time graph, I'll bring the engine back down to idle and shut it down, and we can have a look at this time graph in a little bit more detail.
01:32 So here we can see the area before we've made that change, we can see our injection pulse width starting, our injection event I should say starting at 11.5 degrees, finishing 2.5 degrees before TDC.
01:46 And directly below that we can see our injection fuel pressure at that point, 160 megapascals as we've already discussed.
01:53 Once we can see our new target takes place, we drop down to 80 megapascals, we can see our fuel pressure follows that target which we've requested from our target table.
02:04 And we can see that our start of injection event doesn't change, we're still 11.5, 11.6 degrees before TDC.
02:11 But we can see that in order to get the same mass of fuel delivered into the cylinder, our injector needs to now be open a lot longer, in this case we've increased our injection pulse width by about five degrees in terms of our engine cycle time.
02:28 So we're now closing the injector around about 2.5 degrees after top dead centre.
02:33 Directly above this we can actually see our injection pulse width.
02:37 Prior to dropping the fuel pressure, we're around about 0.75 milliseconds, in order to get that same mass of fuel into the engine, we need to extend that out to 1.17 milliseconds.
02:49 So that's our first test there.
02:50 No real big surprises but we see that as the fuel pressure drops, the injection pulse width needs to increase in order to get the fuel into the engine.
02:59 Let's have a look now and we'll see how our fuel pressure affects that engine performance under a wide open throttle ramp run on our dyno.
03:06 Before we complete our first run on the dyno let's head back across to our fuel pressure target table.
03:11 And we can see here that in the areas that we're going to be operating at during a wide open throttle ramp run, above 2200 RPM and 80 milligrams of fuel delivery, we are running a target fuel pressure of 195 megapascals.
03:27 That's relatively close to the maximum value we can run here on our Toyota 1KD engine.
03:34 Let's get our first run underway, and we'll check out the results.
04:02 OK we've got our first run complete there and we can see on our dyno we registered 181.7 horsepower or 135.5 kilowatts at the rear wheels.
04:11 We've also got our boost pressure up there just as a reference so we'll be able to see if there's any effect on our boost pressure, make sure for our second run that our parameters are as close to identical as we can get them.
04:24 What I'm going to do is save that run and I'll call that base run.
04:29 We'll make a change now to our fuel pressure, and we'll perform another run and see the effect of that change.
04:35 So let's jump back into our laptop software and what I'm going to do here is in the entire area of that target table that we'll be operating at under wide open throttle ramp run, what we're going to do is reduce our fuel pressure target by 50 megapascals.
04:51 So remember this is going to require a larger injector pulse width to deliver the same amount of fuel, which will have the effect of retarding the injection timing or the end of injection point and this has the fuel burning later in the engine cycle, moving our 50% burn point later in the combustion cycle.
05:11 Let's get our second run underway and we'll see the effect of reducing that fuel pressure.
05:37 Alright so we can see our second run's complete there on our dyno.
05:40 We've got 167.2 horsepower at the rear wheels this time.
05:43 Remembering our first run we had So that's a reasonably significant drop in power just for the fact that we've dropped our fuel pressure by 40 megapascals.
05:54 And we can see as well our boost pressure was almost identical on those two runs, we've got a slightly lazier response as we've come up on boost, but predominantly throughout the run the boost pressure has overlaid right on top of the previous run.
06:08 So we're delivering exactly the same mass of fuel into the engine.
06:11 We're only delivering it at a lower fuel pressure hence affecting our injection pulse width and that's given us that dramatic effect on our power.
06:20 Of course we'd also expect to see that exhaust gas temperature and our emissions affected by this change as well.
06:26 So it is important to understand that when we are adjusting the fuel pressure, that these changes are not taking place in isolation, but rather they have an effect on other aspects of the engine's operation as well.

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