Atkinson cycle > how much to get
Atkinson cycle > how much to get
(OP)
Good morning everybody (it's morning here in Poland, so let me start like that), I'm sort of new here. Although I've been reading the forum for quite a time, it's my first post.
I'm on a very early stage of designing an Atkinson 4t engine, the design will be most likely followed by making that engine. Therefore I have a few questions...
1. What efficiency is really possible to get with compression/expansion ratio? I thought of ethanol driven engine with CR 12:1 and ER 25:1. The engine will be anyway small, the issue is maximum achievable efficiency - not gonna be a useless model. I counted theoretical efficiencies as Mr. Heywood advised and did my own real cycle calculations. - The thermal efficiency values seem to grow together with expansion pressure reaching 2.5-3 bar in real cycle. On the other hand, my friend who works as a professional engine constructor suggests much lower ER, claiming that in true engines we don't operate under the pressure of 5 bar. Could you advice me sth?
2. I'm collecting fuel data for ethanol. I know the efficiency-to-AFR curve for petrol. Do you have such curve for ethanol? Where to find it?
Thank you in advance for any tips and hints.
I'm on a very early stage of designing an Atkinson 4t engine, the design will be most likely followed by making that engine. Therefore I have a few questions...
1. What efficiency is really possible to get with compression/expansion ratio? I thought of ethanol driven engine with CR 12:1 and ER 25:1. The engine will be anyway small, the issue is maximum achievable efficiency - not gonna be a useless model. I counted theoretical efficiencies as Mr. Heywood advised and did my own real cycle calculations. - The thermal efficiency values seem to grow together with expansion pressure reaching 2.5-3 bar in real cycle. On the other hand, my friend who works as a professional engine constructor suggests much lower ER, claiming that in true engines we don't operate under the pressure of 5 bar. Could you advice me sth?
2. I'm collecting fuel data for ethanol. I know the efficiency-to-AFR curve for petrol. Do you have such curve for ethanol? Where to find it?
Thank you in advance for any tips and hints.





RE: Atkinson cycle > how much to get
Can you direct us to your reference for the curve you have for petrol?
The problem with an extreme expansion ratio that looks good on paper is that it encroaches on the part of the cycle needed for exhaust blowdown; this will impair volumetric efficiency, thus reducing power density. For your project you might consider building a model in GT Power to evaluate these and other trade-offs.
RE: Atkinson cycle > how much to get
AFR to FC curve I thought about sth like this one: http://w
Exhaust blowdown - sorry, until now I have been mainly calculating 2S engines. I just assumed that in case of having the whole stroke for expelling the burned gases out from the cylinder it's not such a big deal anymore. Especially that the engine is to work on ethanol (I guess VE would go up) and the Atkinson cycle is gonna be achieved by late IC - shouldn't this also keep the VE relatively high?
RE: Atkinson cycle > how much to get
If you have variable intake valve closing timing, you can use that to vary engine torque output by varying the amount of charge that stays in the cylinder, in place of a throttle. Many production engines are already doing this to some extent. Pumping losses are a little lower than by throttling if you do this.
RE: Atkinson cycle > how much to get
RE: Atkinson cycle > how much to get
That's what my questions are about.
RE: Atkinson cycle > how much to get
Regards
Pat
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RE: Atkinson cycle > how much to get
RE: Atkinson cycle > how much to get
Have you considered closing the intake valve early to limit effective CR?