Transient boost pressure (turbocharged gasoline)
Transient boost pressure (turbocharged gasoline)
(OP)
If I subject a gasoline engine to a step change in throttle input (almost closed to wide open) at constant engine speed, what would be the expected shape of the boost pressure vs time curve (assuming no change in wastegate position and stoichiometric operation throughout)?
My thinking is that it should be a step followed by an s-shaped curve. The step is caused instantly by the throttle openning. The gradient should then increase with time as the operating points of the compressor and turbine gradually move from the low to high efficiency parts of their maps. And then the gradient should decrease as the turbo speed settles. This gives a nice smooth s-shaped curve.
Does anyone have any experience of these sorts of transient measurements? Or any useful theories about what should happen and why?
My thinking is that it should be a step followed by an s-shaped curve. The step is caused instantly by the throttle openning. The gradient should then increase with time as the operating points of the compressor and turbine gradually move from the low to high efficiency parts of their maps. And then the gradient should decrease as the turbo speed settles. This gives a nice smooth s-shaped curve.
Does anyone have any experience of these sorts of transient measurements? Or any useful theories about what should happen and why?





RE: Transient boost pressure (turbocharged gasoline)
I'd expect a massive bog if you maintained stoich throughout, in reality.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Transient boost pressure (turbocharged gasoline)
RE: Transient boost pressure (turbocharged gasoline)
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Transient boost pressure (turbocharged gasoline)
What you are left with is an almost stagnant airstream at around atmospheric pressure up stream of the throttle, and an almost stagnant downstream flow at some reasonably low depression.
Snap the throttle open, and what happens ? A sudden spike in flow and a rapid increase in induction pressure, but it will probably depend mostly on the total volume between throttle and inlet valves, and peak flow capability through that throttle.
A really good reason to run individual throttle bodies if possible.
RE: Transient boost pressure (turbocharged gasoline)
RE: Transient boost pressure (turbocharged gasoline)
2.0L 8:1 compression TD04-G (IIRC). 4th gear pull.
CODE
2812 0 -11.8 11.5 23.63
2858 100 6.4 21.0 11.82
2897 100 8.1 19.0 11.82
2925 100 9.1 17.5 11.82
2955 100 10.7 16.5 11.36
2971 100 12.2 15.5 11.24
3016 100 12.9 15.0 11.24
3064 100 13.6 15.0 11.24
3082 100 13.9 15.0 11.24
Sorry I dont have the time to pull up data going from some throttle position that gives stoich AFR at cruise and then the changeover to WOT (wide open throttle).
I have some difficulty with your constraints:
1) constant RPM is only going to happen with a dyno that can increase load as output power/torque is increased. I dont really see that condition as having much value in the real world. And I dont know how you would test it either.
2)The AFR must go rich upon boost/WOT or else the motor will ping itself to death (at least that's what I hear).
RE: Transient boost pressure (turbocharged gasoline)
By constant RPM, I meant reasonably constant RPM, like you'd get in a high gear tip-in. Your's looks fairly constant - do you have an elapsed time column to go with it?
Again, many thanks.
RE: Transient boost pressure (turbocharged gasoline)
You're looking for 5th gear, around 2800-3000 rpm? I'll also normalize the time collumn for ya.
RE: Transient boost pressure (turbocharged gasoline)
RE: Transient boost pressure (turbocharged gasoline)
CODE
0 2834 15.7 -1.2 14.68 33
200 2842 98.0 4.2 15.83 25.5
421 2881 98.4 6.8 11.93 20
591 2867 98.4 7.8 11.93 17
761 2906 98.8 9.3 11.59 16
961 2904 98.8 10.4 11.47 16.5
1172 2934 99.2 11.6 11.24 15.5
1342 2931 99.2 12.6 11.24 14.5
1532 2981 99.2 13.5 11.24 14
1692 2993 99.2 13.9 11.24 13.5
1893 2992 99.2 14.1 11.24 13.5
2073 3025 99.2 13.9 11.24 14
2233 3062 99.2 13.8 11.24 14.5
2414 3064 99.6 13.5 11.24 14.5
2614 3072 99.6 13.5 11.24 14.5
2824 3079 99.2 13.5 11.24 14.5
3004 3112 99.2 13.5 11.24 14.5
3165 3133 99.6 13.6 11.24 14.5
3335 3150 99.6 13.6 11.24 14.5
3535 3185 99.6 13.8 11.24 14.5
3735 3183 67.5 13.6 11.24 14.5
3906 3190 0 6.2 11.24 20
4076 3182 0 -1.7 11.47 31
4276 3183 0 -5.7 25.35 23.5
4486 3183 0 -7.3 23.75 13
4677 3159 0 -8 23.75 11.5
Notes: Gear ratio in 5th is .738:1, Final drive 3.9:1. Average delta time between data points is 187msec. AFR reported using a narrow band (OEM) O2 sensor, IE: not really accurate away from stoich.
Hope thats what you were looking for.
Nick
I love materials science!
RE: Transient boost pressure (turbocharged gasoline)
Absolutely! Couldn't have asked for more. Thanks again.