What is a Yam clone's % efficiency ?

[Sibbo]

What is a Yam clone's % efficiency ? I've been calling it 40 % in calculation and for plugging into this calculator .
http://ecomodder.com/forum/tool-aero-ro ... stance.php

What % would you use ?

[penybryn]

I stand to be corrected, but from data on the internet and assuming that the engine is working at maximum output at 3600rpm (actually this is not true for a motorcycle application because the engine will not be working so hard all the time and the revs will not always be constant if used with a gearbox, more typical of a generator but it gives an idea):

Energy density for diesel fuel = 38.6 Megajoules/litre
Converting to kWh (because it's a unit I am more comfortable with) = 10.7 kWh/l
This is the total amount of energy available in the diesel fuel.

Quoted fuel consumption of 10hp clone at 3600rpm = 0.281Kg/kWh
Convert to litres at density of 0.832 Kg/litre
Fuel consumption = 0.339 litres/kWh
or (inverse) Specific output of engine 1/0.339 = 2.96 kWh/litre

Efficiency % is given by: energy out x 100/energy in
= 2.96 x 100/10.7
= 27.7% (approx)

To compare, a Perkins 402D engine (507cc) has a quoted fuel consumption of 275g/kWh which gives an efficiency of 28.6%

I suggest 30% as a round figure rather than 40%

[Sibbo]

Thank you very much ,I been finding it difficult to get a definite number and my math isn't good enough to derive it as you have .

I've been mucking around with this calculator http://ecomodder.com/forum/tool-aero-ro ... stance.php and some published figures on an old Royal Enfield Dreamliner fairing .The fairing was fitted to a petrol engined 350 cc Enfield and using the data I have I'd like to calculate the drag coefficient of the original fairing .

Something I should have asked earlier ,would you give a 350 aircooled petrol engine an efficiency of 22 % or less ?

[penybryn]

Yes - following the same calculation for a 400cc industrial petrol engine, efficiency comes to 21.5% so 22% is a very good approximation.

[Sibbo]

Thank you very much .