Efficient cylinder size

[inox]

The downsizing is the trend of today's engine design. But how much you can downsize the cylinder size to maintain efficiency of the engine? I have read that too small cylinder size causes inefficient burning of fuel.

I have been playing with the idea of downsizing the current F1 V6 engines from 1.6 to 1.2 liters. In theory it would cause revs to rise from current 12,000 rpm up towards 16,000 rpm. The friction will increase of course and efficiency will suffer somewhat. But how much? Is the reduction in cylinder size from 0.27 to 0.20 liters too much for maintaining sensible efficiency?

In 1994 F1 season Ferrari had by far the most powerful F1 engine, the mighty 3.5 litre V12. However, for next year the engines were downsized to 3 liters and suddenly Ferrari's V12 could not really compete with V10 engines anymore. The cylinder size was reduced from 0.29 to 0.25 liters. The new engine made absolutely wonderful sound, revving up to 17,200 rpm in the latter part of the season. Even though it was probably still delivering more top end power than other, it was now certainly suffering more in overall efficiency.

But what is the situation with today's technology? Are turbo engines as sensitive to small cylinder sizes as naturally aspirated ones?

[J.A.W.]

N/A 4T F1 capacity restricted mills were forced to seek super-high rpm to maintain power output..
( torque X time=power) but forced induction mills can/do substitute higher pressures for rpm & keep 'efficiency'..

The recent plethora of 'high efficiency' 3-cylinder/~1 litre car engines in production - supports your contention though..

[countersteer]

Here's a thought... If we assume a perfect spherical combustion chamber, the ratio of internal volume to surface area increases by the radius of the sphere. Combustion doesn't occur on the walls of the combustion chamber as it is too cold. (the chill zone) A single large cylinder will burn more of the fuel as compared to multiple cylinders totaling the same displacement. A piston/cylinder/head combustion chamber would have an even greater increase in the "cold" surface are per unit volume.

Direct injection will limit this effect as the liquid fuel is injected at the time of combustion.

[J.A.W.]

You'd need a very long stroke, &/or real big boost from forced induction to get a high enough comp' ratio..
& then the heat loss to the working surface area - would still spoil your 'efficiency'..

[PlatinumZealot]

The downsizing is the trend of today's engine design. But how much you can downsize the cylinder size to maintain efficiency of the engine? I have read that too small cylinder size causes inefficient burning of fuel.

I have been playing with the idea of downsizing the current F1 V6 engines from 1.6 to 1.2 liters. In theory it would cause revs to rise from current 12,000 rpm up towards 16,000 rpm. The friction will increase of course and efficiency will suffer somewhat. But how much? Is the reduction in cylinder size from 0.27 to 0.20 liters too much for maintaining sensible efficiency?

In 1994 F1 season Ferrari had by far the most powerful F1 engine, the mighty 3.5 litre V12. However, for next year the engines were downsized to 3 liters and suddenly Ferrari's V12 could not really compete with V10 engines anymore. The cylinder size was reduced from 0.29 to 0.25 liters. The new engine made absolutely wonderful sound, revving up to 17,200 rpm in the latter part of the season. Even though it was probably still delivering more top end power than other, it was now certainly suffering more in overall efficiency.

But what is the situation with today's technology? Are turbo engines as sensitive to small cylinder sizes as naturally aspirated ones?

Was the decrease in competitiveness a result of having less power/efficiency? or less weight?

[tuj]

I think 200cc is about the limit for good characteristics. Having a cylinder displacement somewhere between 200-300cc seems to be about optimal for a racing engine.

[inox]

I think 200cc is about the limit for good characteristics. Having a cylinder displacement somewhere between 200-300cc seems to be about optimal for a racing engine.

I found a nice technical article from an old magazine about different engine configurations. The article is from 1999, but it seems to be pretty valid still, forecasting the coming 3-cylinder era. It says the sensible cylinder size for passenger cars is 250-600 cc. It wasn't mentioned though whether it would make sense to go below the 250 cc in racing engines.

I think it would be really interesting if they could pursue 200 cc cylinder size in F1. It would be a beneficial study for the road car industry, as it will be hard to downsize 4-stroke engines smaller than 600 cc using 3-cylinder format. Going for less cylinders would apparently require a 2-stroke engine?

Reducing F1 engine size from 1.6 to 1.2 liters would mean torque decrease of 25%. So engine and transmission weights could be scaled down considerably, allowing lower weight for the car. What do you think, would it be possible to make such a small turbo engine to produce as much power as the current unit reliably?

[Andres125sx]

...as it will be hard to downsize 4-stroke engines smaller than 600 cc using 3-cylinder format. Going for less cylinders would apparently require a 2-stroke engine?

Why?

There are many 4 stroke bikes with one or two cylinders. I wonder what perfomance may provide a 2 cylinder 0.5l turbo engine... Considering there are 1 litre 3 cylinder engines on production cars providing 115hp and 200Nm (volkswagen golf) it is a feasible configuration for smaller cars

[gruntguru]

Reducing F1 engine size from 1.6 to 1.2 liters would mean torque decrease of 25%. So engine and transmission weights could be scaled down considerably, allowing lower weight for the car. What do you think, would it be possible to make such a small turbo engine to produce as much power as the current unit reliably?

The torque would be dictated mainly by the shape of the fuel flow limit. The present curve dictates approximately constant torque below 10,500 and constant power above. If this rule wasn't changed, a 1.2 litre engine would have almost identical torque (the boost would be higher of course).

[tuj]

yeah but isn't the fuel flow limit going away? Then we could see some real screamers perhaps? High boost 1.2l hybrids?

Or perhaps we could go for ultimate savings and just make the manufacturers put their MotoGP engine via chain drive into their F1 car, sort of like the old days!

[Cold Fussion]

The fuel flow limit isn't going anywhere.

[inox]

Reducing F1 engine size from 1.6 to 1.2 liters would mean torque decrease of 25%. So engine and transmission weights could be scaled down considerably, allowing lower weight for the car. What do you think, would it be possible to make such a small turbo engine to produce as much power as the current unit reliably?

The torque would be dictated mainly by the shape of the fuel flow limit. The present curve dictates approximately constant torque below 10,500 and constant power above. If this rule wasn't changed, a 1.2 litre engine would have almost identical torque (the boost would be higher of course).

Article 5.1.5: "Below 10500rpm the fuel mass flow must not exceed Q (kg/h) = 0.009 N(rpm)+ 5.5."

So if there was only a 100kg/h fuel flow limit and not the rev based limit (see article 5.1.5 above), would they be using even less revs with more boost?

With reliability in mind, which option is easier way to increase power, by adding boost or revs?

Anyway, they would get quite much nicer sounds already by making following small modification to the formula:
Q (kg/h) = 0.008 N(rpm)+ 4

That would mean power reaching peak level at 12000 rpm

[riff_raff]

There are many 4 stroke bikes with one or two cylinders. I wonder what perfomance may provide a 2 cylinder 0.5l turbo engine... Considering there are 1 litre 3 cylinder engines on production cars providing 115hp and 200Nm (volkswagen golf) it is a feasible configuration for smaller cars

Cars with one or two cylinder engines:

http://image.motortrend.com/f/roadtests ... p-view.jpg

https://upload.wikimedia.org/wikipedia/ ... e_room.jpg

http://www.curbsideclassic.com/wp-conte ... hassis.jpg

http://www.americanbantam.com/images/Me ... mitt_1.jpg

http://photos1.blogger.com/blogger/5107 ... _motor.jpg

Here's a modern down-sized, two cylinder, two-stroke, 730cc turbo diesel engine:

http://www.autocar.co.uk/car-news/indus ... uture-tech