If you can predict the pressure then you have predicted the power(less
friction
if you use IMEP) normally the equation is reversed using stated power to
compute the BMEP (Brake meam effective pressure) . This is often used
as a reality check on advertised power of normally aspirated engines
(with boosted or nitro'd engines you can dial any amount of power
you want - right up to distruction) - I once wrote an article for
Contact
magazine titled "Seperating the BS from BHP with BMEP"
Wankels are pressure/area/volume expansion engines like all the
rest, and the same rules apply - Vance
Norman DeBoer writes:
Thank you Vance for your response. Yes, all that you say is correct.
The first item P = 146 is the predicted pressure (IMEP) for the Zoche
Aero
Diesel engine. All the rest of the parameters are given or are claimed
(300 HP). Could something like the PLANK/33000 formula be developed for
the
Rotary Engine?
As inferred above, all the same basic rules apply to any form of
positive
displacement expansion engine. Since we do not have classic bore and
stroke, the
equivalent is the swept volume of an individual cylinder/chamber cubic
inches, divided
by 12 (this is our LA) NK then becomes the number of expansion
completions (power
strokes) per turn of a reference shaft times the rpm of that shaft. The
Wankel output shaft
turns 3 times for each turn of the trochoid rotor, and each of those
turns makes 3 complete 4 stroke cycles (3 power" strokes") for each of
the two rotors in
a Mazda 13B. so there are 2 power expansions per each turn of the output
shaft.
Each expansion displacement is half the "rated "1.3 liter displacement,
or 39.65 cubic inches
thus with 133 psig bmep (typical normally aspirated value for a
production automobile engine),
and 6000 rpm we have:
133 psig * (39.65/12 ) * 2 per rev * 6000 rpm / 33000 = 159.8 hp
Which is about what a late model stock RX7 engine will do.
Vance
====================================================
Vance:
Is this what the formula should be for a 20B then?
133 psig * (39.65/12 ) * 3 per rev * 6000 rpm / 33000 = 221.6 hp
1.3 Liter 1.2 Liter 1.9 Liter
RPM PSIG 13B HP RPM PSIG 12A HP RPM PSIG 20B HP
800 133 21.3 800 133 19.7 800 133 29.6
900 133 24.0 900 133 22.2 900 133 33.2
1000 133 26.6 1000 133 24.6 1000 133 36.9
1100 133 29.3 1100 133 27.1 1100 133 40.6
1200 133 32.0 1200 133 29.6 1200 133 44.3
1300 133 34.6 1300 133 32.0 1300 133 48.0
1400 133 37.3 1400 133 34.5 1400 133 51.7
1500 133 40.0 1500 133 36.9 1500 133 55.4
1600 133 42.6 1600 133 39.4 1600 133 59.1
1700 133 45.3 1700 133 41.9 1700 133 62.8
1800 133 47.9 1800 133 44.3 1800 133 66.5
1900 133 50.6 1900 133 46.8 1900 133 70.2
2000 133 53.3 2000 133 49.3 2000 133 73.9
2100 133 55.9 2100 133 51.7 2100 133 77.6
2200 133 58.6 2200 133 54.2 2200 133 81.3
2300 133 61.3 2300 133 56.6 2300 133 85.0
2400 133 63.9 2400 133 59.1 2400 133 88.7
2500 133 66.6 2500 133 61.6 2500 133 92.3
2600 133 69.2 2600 133 64.0 2600 133 96.0
2700 133 71.9 2700 133 66.5 2700 133 99.7
2800 133 74.6 2800 133 69.0 2800 133 103.4
2900 133 77.2 2900 133 71.4 2900 133 107.1
3000 133 79.9 3000 133 73.9 3000 133 110.8
3100 133 82.6 3100 133 76.3 3100 133 114.5
3200 133 85.2 3200 133 78.8 3200 133 118.2
3300 133 87.9 3300 133 81.3 3300 133 121.9
3400 133 90.6 3400 133 83.7 3400 133 125.6
3500 133 93.2 3500 133 86.2 3500 133 129.3
3600 133 95.9 3600 133 88.7 3600 133 133.0
3700 133 98.5 3700 133 91.1 3700 133 136.7
3800 133 101.2 3800 133 93.6 3800 133 140.4
3900 133 103.9 3900 133 96.0 3900 133 144.1
4000 133 106.5 4000 133 98.5 4000 133 147.8
4100 133 109.2 4100 133 101.0 4100 133 151.4
4200 133 111.9 4200 133 103.4 4200 133 155.1
4300 133 114.5 4300 133 105.9 4300 133 158.8
4400 133 117.2 4400 133 108.4 4400 133 162.5
4500 133 119.9 4500 133 110.8 4500 133 166.2
4600 133 122.5 4600 133 113.3 4600 133 169.9
4700 133 125.2 4700 133 115.7 4700 133 173.6
4800 133 127.8 4800 133 118.2 4800 133 177.3
4900 133 130.5 4900 133 120.7 4900 133 181.0
5000 133 133.2 5000 133 123.1 5000 133 184.7
5100 133 135.8 5100 133 125.6 5100 133 188.4
5200 133 138.5 5200 133 128.1 5200 133 192.1
5300 133 141.2 5300 133 130.5 5300 133 195.8
5400 133 143.8 5400 133 133.0 5400 133 199.5
5500 133 146.5 5500 133 135.4 5500 133 203.2
5600 133 149.1 5600 133 137.9 5600 133 206.9
5700 133 151.8 5700 133 140.4 5700 133 210.5
5800 133 154.5 5800 133 142.8 5800 133 214.2
5900 133 157.1 5900 133 145.3 5900 133 217.9
6000 133 159.8 6000 133 147.8 6000 133 221.6
6100 133 162.5 6100 133 150.2 6100 133 225.3
6200 133 165.1 6200 133 152.7 6200 133 229.0
6300 133 167.8 6300 133 155.1 6300 133 232.7
6400 133 170.5 6400 133 157.6 6400 133 236.4
6500 133 173.1 6500 133 160.1 6500 133 240.1
6600 133 175.8 6600 133 162.5 6600 133 243.8
6700 133 178.4 6700 133 165.0 6700 133 247.5
6800 133 181.1 6800 133 167.5 6800 133 251.2
6900 133 183.8 6900 133 169.9 6900 133 254.9
7000 133 186.4 7000 133 172.4 7000 133 258.6
7100 133 189.1 7100 133 174.8 7100 133 262.3
7200 133 191.8 7200 133 177.3 7200 133 266.0
7300 133 194.4 7300 133 179.8 7300 133 269.6
7400 133 197.1 7400 133 182.2 7400 133 273.3
7500 133 199.8 7500 133 184.7 7500 133 277.0
7600 133 202.4 7600 133 187.2 7600 133 280.7
7700 133 205.1 7700 133 189.6 7700 133 284.4
7800 133 207.7 7800 133 192.1 7800 133 288.1
7900 133 210.4 7900 133 194.5 7900 133 291.8
8000 133 213.1 8000 133 197.0 8000 133 295.5
8100 133 215.7 8100 133 199.5 8100 133 299.2
8200 133 218.4 8200 133 201.9 8200 133 302.9
8300 133 221.1 8300 133 204.4 8300 133 306.6
8400 133 223.7 8400 133 206.9 8400 133 310.3
8500 133 226.4 8500 133 209.3 8500 133 314.0
8600 133 229.0 8600 133 211.8 8600 133 317.7
8700 133 231.7 8700 133 214.2 8700 133 321.4
8800 133 234.4 8800 133 216.7 8800 133 325.1
8900 133 237.0 8900 133 219.2 8900 133 328.7
9000 133 239.7 9000 133 221.6 9000 133 332.4
9100 133 242.4 9100 133 224.1 9100 133 336.1
9200 133 245.0 9200 133 226.6 9200 133 339.8
9300 133 247.7 9300 133 229.0 9300 133 343.5
9400 133 250.4 9400 133 231.5 9400 133 347.2
9500 133 253.0 9500 133 233.9 9500 133 350.9
9600 133 255.7 9600 133 236.4 9600 133 354.6
9700 133 258.3 9700 133 238.9 9700 133 358.3
9800 133 261.0 9800 133 241.3 9800 133 362.0
9900 133 263.7 9900 133 243.8 9900 133 365.7
10000 133 266.3 10000 133 246.3 10000 133 369.4
If you could keep the bmep at that value over those rpm values, which you
cannot,
then those numbers would be valid. You lose bmep at low rpm because the
port timing will cause back flow, and at higher rpm because you cant "suck"
a full "breath" that fast. This is like the previous posting - Vance
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