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Intake - Charging
In the Exercise 14 , we have looked at the compression stroke more closely. In addition to the working stroke it is particularly
exciting. It was about the temperature increase, which were ultimately caused by increasing the pressure. We want to take care of that now for the petrol and diesel engine, both without and with supercharging.
The isentropic exponent Κ the heat capacity with volume change work devided by it without volume change. Of course, the heating upto a certain temperature (= heat capacity) needs more energy with the
volume change work. See how Κ of air is calculated:
p1
(relativ) | p1
(absolut) | p2
10:1 (petrol) |
p2
13:1 (petrol) | p2
16:1 (Diesel) |
p2
19:1 (Diesel) |
| -0,1 bar | 0,8 bar | 20,1 bar | 29,0 bar | 38,8 bar | 49,4 bar |
| -0,2 bar | 0,9 bar | 22,6 bar | 32,6 bar | 43,7 bar | 55,6 bar |
| 1,0 bar | 2,0 bar | 50,3 bar | 72,5 bar | 97,0 bar | 123,4 bar |
| 1,5 bar | 2,5 bar | 62,8 bar | 90,7 bar | 121,5 bar | 154,4 bar |
| 2,0 bar | 3,0 bar | 75,4 bar | 108,8 bar | 145,5 bar | 185,3 bar |
| 2,5 bar | 3,5 bar | 62,8 bar | 126,9 bar | 170,0 bar | 216,1 bar |
| 5,0 bar | 6,0 bar | 150,8 bar | 217,6 bar | | |
The first column reflects what a measuring device would indicate. Of course in such formularies you always have to start from absolute pressure. You can also take all the pressures with 1,000 times, then you have
hPa. Not so much difference, however, whether one runs from 0.8 or 0.9 bar.
But then the charging is added, whether it is turbo or compressor. The next two lines apply to the rather moderate charge pressure of the gasoline engine. Now you know why they often take back geometric
comprssion. The knocking limit would otherwise be significantly exceeded. Exactly in pressure you can not specify it because it is still dependent on other factors such as e.g. the combustion chamber shape.
Then two lines of the diesel, crossing the higher pressure more belonguing to the truck. The same applies to the geometric compression as with the petrol engine. The diesel uses the pressures to reach its highest
torque at an early rpm and then regulate the boost pressure. However, it is also clear that this is in the case of the diesel is limited by the material (which in the meantime still better) instead of a knocking limit.
And what are the 5 or 6 bar at the bottom? This was allegedly the highest load pressure of the F1-BMW a long time ago in one of its qualifying engines. However, its geometrical translation ratio is unrecognized and if
it has destroyed not itself, too. By the way, the engine block from GG (!) descends from the first BMW 1500. But they only took not new ones but for a long time used blocks. 02/17
| All cooling ingredients of course allow a higher load pressure. |
| BMW S55 with water injection and optimized intercooling |
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