“An opposed-piston two-stroke was considered for a GP car in the 1920s”
Pat Symonds recently dropped the bombshell that Formula 1 is seriously looking at two-strokes for its next engine formula, post-2025.
Forget the smoky old Saabs and DKWs that were effectively regulated out of the road car market in the late ’60s/early ’70s by emission and economy requirements. For one thing, these would be opposed-piston two-strokes with the combustion chamber between them, meaning the oil would not be part of the same mixture as the fuel, as was the case with those old engines where the combustion chamber was around the crankshaft, and they would not be throwing any more unburnt fuel out of the exhaust than a four-stroke. For another, modern developments in forced induction and computer-controlled ignition and timing are quite capable of curing the residual downsides of the two-stroke and potentially leaving F1 to enjoy some very real upsides.
Such an engine would be inherently more efficient than a four-stroke, as Symonds notes: “It’s reasonably obvious that if you are going to pump that piston up and down, you might as well get work out of it every time the piston comes down rather than every other time the piston comes down.”
Variable geometry turbines and software-controlled ignition are just two of the more obvious current technologies perfectly suited to maximising the potential of the two-stroke. The workings of such an engine lend themselves to cylinders of much bigger bore:stroke ratios than currently, giving very low piston speeds for a given rpm.
Already, working prototypes in the automotive industry are achieving well in excess of 50 per cent thermal efficiency – which is where current hybrid F1 four-stroke engines are, but helped by the energy recapture from the ERS-K and ERS-H systems. It’s not too much of a leap to imagine in excess of 60 per cent from an F1 forced induction, opposed-piston two-stroke with all the energy-recapture technology of current engines. That would be a remarkable achievement, but it goes beyond that. Because the two-stroke is inherently more powerful for a given capacity, the engines could be downsized – thus these massive thermal efficiencies would be applied to a smaller engine so the actual economy gains would be immense.
“Imagine a 20,000rpm supercharged 1-litre three-cylinder of 1000bhp“
Furthermore, because the two-stroke has no cylinder head it is physically much smaller for a given capacity. Smaller, lighter engines requiring nowhere near as much fuel would address one of the major failings of current cars, which is that they are just too big and heavy. Lighter, more agile cars would not only be more raceable, but would give the tyres an easier time, making it more feasible for the tyre manufacturer to come up with something that could be raced hard for the whole distance.
Because of the way the exhaust pulses work, the best two-stroke power efficiencies are achieved with three cylinders (or multiples of three). The exhaust note of a small, high-revving, three-cylinder would be out of this world, unlike any sound previously associated with F1. Imagine a 20,000rpm, turbo/supercharged, 1-litre three-cylinder of 1000 horsepower.
The potential for development of such a new combination of technology would be immense and so therefore would be the potential development cost. But much of it would also be relevant to automotive industry and so one can imagine the tricky discussions that might ensue about which R&D car manufacturer spend was for automotive and which was for the F1 programme. But that’s surely a solvable problem.
Until the planet’s electricity generation is fully weaned off fossil fuel and the problems solved of the massive increase in electrical consumption that would result in all road cars being electric, the all-electric car is not the full answer. Two-strokes look set to have a real relevance to the automotive industry. Symonds believes than an F1 two-stroke car, running on synthetic fuel, would actually be greener than a Formula E car.
As a further reminder that there’s nothing new under the sun, the first time an opposed-piston two-stroke engine was considered for a Grand Prix car was in the 1920s. In 1924 Fiat was working on such an engine: six cylinders, 1.5-litres, supercharged, with 12 pistons sharing six communal combustion chambers, with two cranks geared together (the engine would have been mounted vertically!). One piston in each cylinder would alternately expose/seal the inlet port and the other would do the same with the exhaust port. The ports would be placed in a way that would see the inlet ports open (with high forced induction-aided pressure) just after the exhaust, helping scavenge the chamber. Fiat was forced to abandon the project because of problems with piston crown cooling. Because the inlet ports could open only for about half the time of a four-stroke and a piston was always exposed to exhaust heat, it would overcome the cooling of the exhaust pistons (which were oil-cooled). But that was with the materials technology and understanding of almost a century ago. It’s surely time we revisited the idea.
Since he began covering grand prix racing in 2000, Mark Hughes has forged a reputation as the finest Formula 1 analyst of his generation