http://not2fast.wryday.com/turbo/glo...rbo_calc.shtml

This program seems to be well done, and includes effects of water injection (Ken).

Notes:

1) use 94mm bore and stroke, 4 cyl, for 1.3L rotary simulation. Argue someplace else.

2) use sfc of about .65 and a/f of 10:1 for starts, but these 2 variables are related. Running leaner makes more hp more efficiently, and the sfc must be increased to properly reflect the power increase. Best to just leave these alone, and vary other parameters.

3) 255 hp stock?

10:1 a/f
.65 sfc
10 psi
21C ambient
75% compr eff
60% IC
6500 rpm
80% VE
1 psi IC drop

 

WOW, great program.

Just what I was looking for.

Ken

 

Yup fantastic program. I use it often

Checks out with other formule & spread sheets I use. Infact I find it easier to use as its all rolled into one sheet (very handy).

Still only as good as the data you have though

 

good site guys

 

Thanks !
What bore and stroke should i use for a 12A ?

Karis

 

So you techno types have found that a rotary engine is comparable to a "square" piston engine as far as number-crunching is concerned? (Not an arguement, just a clarification which would also help answer the question above about the 12A).

 

Its not applicable to the formula, just input in a number into the bore or the stroke field untill you get the 4 stroke equivalent displacement for your rotary engine of choice.

The calcs do not determine anything bare the displacement fromt he bore/stroke fields, the rest is info you need such as BSFC & Ve from either another source or testing of your own.

 

OK, I guess that website doesn't compensate for bore/stroke differences for a given displacement. However, some calculations do, because I have used such correction factors on aviation piston engine equations. However, it was over 10 years ago, and I can't remember exactly what was affected. I was just wondering how the rotary engine compared to the various bore/stroke ratio of piston engines in this respect.

 

dumb question, in the calculation i can get like 200more hp by making the afr 1:1, but in real life it wouldnt even run that rich, what am i missing?

mike

 

The program probably just computes the HP by dividing out the mass airflow by the AFR to calculate the fuel flow, and then multiplying by the BSFC. This is my personal lazy method with my sophisticated Windows calculator, lol. You can check this by seeing if a 10:1 AFR results in twice the horsepower of a 20:1 AFR with everything else remaining the same.

There is probably no limit on the AFR so that the calculator works with any type of fuel (pump gas, race gas, methanol, nitro, etc.).

Also, in reality the BSFC will change with changes in the AFR, rpm, load, and other conditions.

 

thats exactly what it does, 20:1 is half of 10:1

mike

 

I'm using the program to see the relative increases in power for things like cold air intake, better IC, water injection flow increases and where to inject water and water spray and electric fan on IC. In other words the colder the air intake the more power.

It's kinda of a calculator to see the effects of different mods for me.

 

You need an AFR/BSFC relationship, otherwise YES the lower the AFR the more power you will have but this does not work like this in real life

These are the real life or factual data you will need to use that "part" of the program to be "realistic"

ALL else can be used pretty well

Good questions, and again bloody great program mate

 

... missing note #2 in the original post.

2) use sfc of about .65 and a/f of 10:1 for starts, but these 2 variables are related. Running leaner makes more hp more efficiently, and the sfc must be X(increased)X to properly reflect the power increase. Best to just leave these alone, and vary other parameters.

but I should have said "... sfc must be DECREASED to properly reflect the power increase. " (with leaner a/f input).

 

low bore/stroke favors low end torque, high (F1) favors top end hp.

Knowing the eccentric shaft offset is only .59", and power cycles are 270 deg vs 180 deg for piston engine, I say a starting place for comparison is a 6 cyl 2.6L with 5.35" pistons, 1.18" stroke. More oversquare than an F1 engine.