Valves in a spin

Developments in cylinder valve technology suggest there could be life left in the old combustion engine yet. Jon Excell reports.

Since the age of 12 Kingsley Wright has been fine-tuning an idea that has the potential to make the internal combustion engine more efficient, more powerful and more environmentally friendly.

Now, 18 years on, the final pieces of the jigsaw are almost in place, and Wright, the self-proclaimed ‘saviour’ of the combustion engine, is certain that he stands on the brink of global success.

At his company in Wales, Roton Engine Developments, Wright has developed an innovative valve concept for the IC engine; a system where the intake and exhaust valves of a conventional IC engine are replaced with a rotary valve – a vented rotating shaft attached to the engine’s crankshaft.

Throughout the history of the car the poppet valve has dominated combustion engine design. In a conventional piston engine the rotation of the camshaft opens a spring-loaded poppet valve that enables the fuel/air mixture to enter the combustion chamber. The camshaft then closes this valve during the compression and combustion stroke of the cylinder and opens a second spring-loaded valve to vent the cylinder after ignition.

However, the poppet valve is not without its problems. First, it requires a large number of mechanical components including camshafts, lifters, pushrods, rocker arms, valve springs and seals. These components generate heat and noise, and limit the overall speed at which the engine can operate.

One of the main reasons for this is that as revolutions of the engine increase, the ability of poppet valves to open and close in time decreases in efficiency to the point where power output cannot increase further. The size and location of the valves also limit the total volume ofair/fuel mixture allowed into the combustion chamber.

With his Roton system Wright has replaced the poppet valves and camshafts with a rotating valve located within a guideway in the cylinder head. This rotating valve, or shaft, contains a number of holes, or ports, which, depending on the valve’s position as it rotates, alternately provide a link between the combustion chamber and either the exhaust or inlet manifolds.

By co-ordinating the rotation of the shafts and properly positioning the intake and exhaust ports relative to the shafts or holes, a combustible mixture of fuel and air is allowed into the combustion chamber, burnt and then exhausted.

Clearly one of the most important things here is the seal between the valve and cylinder head. This must be absolutely airtight to avoid loss of compression. Poppet valves, despite their attendant disadvantages, actually do this reasonably well – and perhaps this is the reason why they’ve survived for so long.

However, the key to Wright’s invention is a sealing mechanism that allows the rotary valve to rotate freely while still creating an air-tight combustion chamber. Wright explained that while most previous attempts at creating a rotary valve focused on using the shaft as the seal, he concentrated on the cylinder head instead.

So in the Roton, the cylinder head contains a seal that moves from a non-sealing position, in which it is moved away from the valve, and a sealing position, in which it is forced on to the valve by gaseous pressure from within the cylinder.

Wright was unwilling to go into the specifics of the sealing system but he admitted that its performance is largely thanks to the application of an innovative material technology.

Whatever the method, the improvementsare indeed impressive, and perhaps most noticeable is the reduction of engine-related noise and vibration thanks to the removal of the valvetrain.

By replacing one of the biggest causes of engine noise the car designer is then able to remove the heavy sound-deadening material used in today’s vehicles and make more efficient use of the space.

However, the most significant advantage is clearly imparted by the valve itself. In a rotary valve engine the flame front is not in contact with a stationary poppet valve – which just presents one face to the flame and so works at constantly high temperatures.

The rotating valve travels out of the combustion area as the shaft spins, and transfers heat to the cooling system.

Because of this, the ignition of fuel can occur far closer to the highest point of the piston during its stroke than when a red-hot poppet valve is in a race with the spark plug to detonate the fuel.

According to Wright, it is this single piece of freedom – the ability to run at higher compression ratios – that gives a Roton-equipped engine a huge power advantage over a poppet-valve engine.

The inventor added that the technology may also stimulate the use of bio-fuel (derived from crops). Thebeauty of this kind of fuel is that it is carbon neutral, and therefore doesn’t contribute towards the greenhouse effect. One of its disadvantages has been that it doesn’t produce as much portable power as fossil fuels.

Wright said that his team has identified a technique to enable an engine equipped with a rotary valve system to run exceptionally cleanly.

‘This idea allows you so much more flexibility when it comes to raising the compression ratio that you can run it on grown oil and still get better performance than you have now with conventional engines,’ he said.

While engineers have been working on rotary valve concepts for years, Wright suggested that the concept has been stymied by the sealing problem. By solving this and taking the best ideas from a number of developments,Wright claimed that he has developed a concept with great commercial promise.

The dream started to become reality when a550cc motorcycle equipped with the Roton rotary valve cylinder head was driven by his friend’s son in theBritish Supermotard event.

Wright said the engine modifications for the bike’s single-cylinder engine have been relatively easy to make, and that the lessons learned from this will be carried over relatively quickly into the development of a multi-cylinder engine.

He has already built two Roton systems for a K-series Rover in his workshop and the figures are impressive. ‘When I told a guy who tunes K-series cylinder heads that I managed to get this to breathe at 188ft^2per minute out of an 1,800 K-series he nearly fell off his chair, because straight off the factory floor the figure is 75ft^2 per minute.’

But Wright is not alone. US company Coates International has also developed a variation on the rotary valve theme.

Based on ideas developed by company founder George Coates, the Coates Spherical Rotary Valve System (CSRV) also does away with poppet valves, but replaces them with spherical valves that rotate in a cavity formed between a two-piece cylinder head.

Each spherical valve rotates against a matching seal between it and the piston, one for intake and one for exhaust. The spheres have cavities and ports machined into them for the induction of fuel and air on the intake stroke, and the evacuation of fired gases on the exhaust stroke.

The system uses a seal at the intake and exhaust ports of the cylinder to prevent pressure leakage. This two-piece seal contacts with the peripheral surface of the rotary valve and uses the compression and expansionof the fuel and air mixture to create a gas-tight seal with the valves.

The system boasts the same advantages as the Roton. It is said to improve efficiency and power output, reduce emissions and lubrication requirements, be cheaper to manufacture and suitable for retrofitting to combustion engines of all sizes. Like the Roton it also dispenses with hundreds of components that make up the valvetrain on conventional engines.

The company has completed several engine prototypesequipped with the CSRV, five for cars and two for motorcycles. The most recent car prototype hasbeen started over 7,000 times and has been road tested over 40,000 miles. The motorcycle engines were retrofitted for a major motorcycle manufacturer.

But Wright is sceptical about its chances of success. ‘Ours is cheaper, more reliable and doesn’t add inertia to the engine,’ he said. In his view, the spheres on the CSRV are more difficult to manufacture and take up more space than his system, plus their operation means that the air still has to turn through 90 degrees.

This, he claimed, means that the CSRV doesn’t breathe as well as the Roton.

Ultimately, Wright thinks that the Coates system is just too different. While he agreed with Coates that it’s certainly an improvement on existing technology he added: ‘It’s like trying to introduce a rotary engine – a great idea, but one that is too radically different to be guaranteed public acceptance.’

Wright is a lot more optimistic about the future of his own technology. This is perhaps inevitable, but it’s hard not to be swept along by his enthusiasm. In the short term there’s a lot of interest in Roton, although its inventor is tight-lipped about who’s involved – just that it’s ‘a very well-known English sports car manufacturer with interests in other parts of the world’ that is about to get ‘seriously involved’.

In the longer term, Wright’s aims are nothing less than global domination. ‘In three or four years’ time our system will be under the bonnet of every single car in the world,’ he predicted.