Engine design

[zeckgx]

Question: What disadvantages would there be to having a 1.6L 3 Cyl? I only ask because it appears that most manufactures are shifting to 3Cyl power plants. As a result I wouldn't be surprised if If the next major engine change would be to a 1.2ish 3 cylinder. Thoughts?

[tommeke_B]

Question: What disadvantages would there be to having a 1.6L 3 Cyl? I only ask because it appears that most manufactures are shifting to 3Cyl power plants. As a result I wouldn't be surprised if If the next major engine change would be to a 1.2ish 3 cylinder. Thoughts?

Manufacturers are trying to get the maximum efficiency for their engines (best performance, lowest fuel consumption and emissions). Now it seems that with smaller cylinder capacities 3cylinder engines are better. I heard that somewhere below 350cc/cylinder it makes sense going to 3 cylinders (less weight, friction etc), and that's what all manufacturers are doing now, maybe the manufacturing cost has something to do with it as well. FIA is following the car market when they making/changing regulations, in my opinion they react quite late. For example the switch from 2L WRC to 1,6L WRC cars took too long IMO. The small 1L Ecoboost engine of Ford is already used in their new Fiesta R2. Strong rumors claim that Citroën will make a successor of the C2 R2Max next year, using the 1.2 PureTech engine. For R2 it's clear that these small engines are the future. For WRC/R5 it doesn't really make sense to downgrade even more, as the cars still need to be fast enough, and it's probably impossible to get the same performance with even smaller engines than they're having now. Also 1.6T engines are used in the sporty versions of the cars used in rallying now, I think they're good for plenty more years now.

[Rallyper]

I´m not specialist but heard former SAAB (and Volvo engine constructor) Per Gillbrand once said on a seminar that optimal is 500cc/cyl, which could make a 3 cyl 1500 cc engine an advantage.

[itix]

Well one major advantage of the engine being 3 cylinder rather than 4 is weight and size meaning you have more freedom of placement of it and it's ancillary components. You would naturally get a loss of torque (or low end power as I prefer to call it) from a smaller displacement engine. Engine power is dependent on average pressure, revs and volume of a given engine. That means that to compensate for loss of volume you'd have to ramp up the pressure with higher boost and higher engine speeds but that would also mean that the air flow going into the engine would need some optimization so I guess also a hike in restrictor size (I am not used to work with restrictors so I don't really know, but I know someone I can ask...).

[itix]

And I should point out that you can't actually ramp up the pressure infinitely because the fuel and its tendency to knock sets a limit! I suggest hybrid systems if they are to downsize!

[Rollo]

I´m not specialist but heard former SAAB (and Volvo engine constructor) Per Gillbrand once said on a seminar that optimal is 500cc/cyl, which could make a 3 cyl 1500 cc engine an advantage.

Honda did some experiments in the early 1990s and concluded that the optimal was 298cc/cyl; hence the reason why they preferred a 3.5L V12 (291cc/cyl) but a 3.0L V10 (298cc/cyl). When the official capacity in F1 was dropped in 1995 from 3.5L to 3L, practically all the V12s disappered and eventually everyone ran V10s.

Maybe BMW have some new design system inside their cylinders. Mazda changed theirs in their SkyActive cars to prevent knocking; so that doesn't surprise me/

[zeckgx]

I guess the torque of a 1600T 3Cyl would be lacking compared to the current 4cyl. Unless this can be made up by some higher compression ratio.

[Lundefaret]

I guess the torque of a 1600T 3Cyl would be lacking compared to the current 4cyl. Unless this can be made up by some higher compression ratio.

I am no engine expert, so bare with me, but wouldn't the torque of a three cylindre 1.600 ccm be better than that of a four cylindre 1.600 ccm, but the top end be lesser?

[itix]

If I'm not completely wrong, the torque (or low end power) vs top end power has more to do with the bore/stroke ratio than the actual number of cylinders. Obviously compression is what limits the engine as you can't compress endlessly due to the fuel that would begin to knock but you can play with bore and stroke.

A higher stroke generally leaves you with more bottom end power and more "torque" but limits revs due to the limit of the piston average speed, while shorter stroke and wider bore gives you more top end power and higher revs but a narrower power band and less "pull".

I don't have much experience with different cylinder numbers of the same stroke/bore ratio so I can't tell you the difference there. I do however know that you get a "fatter but shorter" engine since the bore would increase to accommodate the same volume in three cylinders. Theoretically there is less friction in a 3cyl engine, but also a less smooth power delivery.

Dunno if we have this expertise in the forum but I'll throw the question out anyway... with modern multipoint direct cylinder injection and all that, what limits us from developing an engine that has very high compression and ignites the fuel on injection? theoretically it should be possible. I know that we are already developing engines with variable compression by varying the height of the engine block so how hard can it be?

[Mirek]

I'm no expert at all but I think that the HCCI engines with petrol auto-ignition at high compression aren't yet developed so much that they could be used in vehicles. I think I read somewhere that main issues are engine wear, very small power range and difficult cold starts.