Design and Development of Exhaust Valves for Internal Combustion Engines from the Perspective of Modern Thinking: Part 2 1930–90

Abstract

The changes in high temperature materials for exhaust valves resulted from the development of the engine fuels. Ricardo and Midgley were the early pioneers of fuel improvement, but later on Houdry and Pines invented processes for upgrading straight run gasoline. None of the early alloys used for valves was specifically invented for that purpose. Marsh developed nickel-based alloys for a thermopile; Haynes, the Stellite series of cobalt alloys as ultrahard and corrosion-resistant materials; Brearley 12Cr martensitic stainless steels for erosion resistant gun barrels.

In the 1920s, the automotive sector began to use Silchrome, which had good resistance to non-leaded fuels. However it was barely adequate in aero engines, and this stimulated the invention of sodium-cooled valves by Heron. Fuels containing tetraethyl lead, invented by Midgley, became standard during the 1930s, but lead from the combustion process was highly corrosive to Silchrome. A British austenitic alloy, KE965, proved to be much better, but during WWII this had to be given high nickel coatings. The Americans developed a material similar to KE965, but for high output radial engines used Inconel M and Stellite coatings.

The post-war era has been dominated by the automotive sector. Low nickel austenitics superseded KE965, but Silchrome is still in use for inlet valves. Zero lead fuels caused problems with ‘valve seat recession’ which has been overcome by induction hardening of cast iron seats, or by incorporating seat inserts. High performance cars have adopted Inconel and Nimonic alloys and sodium cooling, but lightweight titanium alloys are being used to give the ultimate in capability.

Keywords:

• poppet valves
• IC engine fuels
• Silchrome
• KE965
• Stellite
• nickel-based alloys
• sodium cooled valves
• exhaust valve corrosion
• valve seat recession

Acknowledgements

To the unknown reviewer of Part 1 who asked pertinent questions about valve stresses. To Ed Marshal and Bryan Lawton who did an initial informal review of what was a very long paper. And to the Editor for agreeing that this monograph on exhaust valve development be published in several parts in the Newcomen Journal.

Discussion

Dan Hayton: What is the difference between internal combustion engines and jet engines in terms of the temperatures and what the alloys are trying to deal with?

Author: There is definitely a connection between the development of valve materials and turbine blade alloys. Because of preignition the aim was to produce valve materials which would have the highest possible strength at a relatively low temperature, say something like 600 to 700°C. That is why it took such a long time for the nickel-based alloys to be used, since they come into their own in the 750 to 900°C range. In a jet engine, because of the need to minimize the cooling requirements, you need turbine blade material capable of running at 750° and ideally 800–850°C.

Sir Frank Whittle knew that his father (who had run a small jobbing machine shop) had been involved with people building racing and sports cars, and had made valves using the best high temperature alloys. So Sir Frank, when being told that a jet engine would need ‘impossible’ materials, could say ‘my father is using these materials’. So there is a very nice, although indirect, engineering connection between valves and turbine alloys.

Member: Did they experiment at all with exhaust valves which are larger than the inlet valves, the point being that it would have more thermal capacity?

Author: The bigger the valve, the more heat is flowing into the valve, and the more difficult it becomes to disperse the heat. In large spark-ignition stationary engines (not diesel engines), valve temperature limits engine output.

Edward Field: You handed some valves around with a magnet. In some cases the valve head is non magnetic, but the stems are magnetic Are these made of different materials?

Author: The upper part of the stem material is cheaper, and is magnetic because it has a martensitic structure. In this region of the valve the main requirement is for high hardness to resist wear as the valve moves up and down in the guide. The temperature resistant, austenitic alloy, which is non-magnetic, is used in the lower stem and crown.

Neil Barton: I have three questions. You said that the Ford Anglia was built in 1955 but one of the valve samples you handed round was for a 1959 Ford Anglia. Also at the beginning of your talk you showed a big American valve from a Wright 3350 radial, and a British valve from the Merlin, and you joked that ‘there were no prizes for guessing which was which’. Is there a cultural difference, like that with Mobile Phones, where Motorola tended to produce large clunky phones, and Europe designed small things? The third question how did German aircraft engines differ from those of the British?

Author: Ford’s produced various cars, all using the same type of side-valve engine, with different bores and strokes, and each of the model names Popular, Prefect, and Anglia were used for a progression of cars, which makes it confusing. However the engine in the 1959 Anglia was an entirely new design, and used overhead valves.

The Allies had developed methods of producing intrinsically better fuels of a high octane rating using sophisticated techniques for modifying the chemical structure of poor quality petroleum feedstocks. TEL was added to improve octane rating still further. The British were able to use these very high quality fuels, so Allied engines ran at a much higher power output. [At this point a member pointed out that the Germans made much of their fuel from coal, which if done by hydrogenation route should give fuel of quite a high octane rating.] However, even so, the German fuels were not that good (c. 96 octane), and got high power output by nitrous oxide and oxygen injection.

[Since the meeting, the author has obtained a wartime book Metallurgical Study of German and Italian Aircraft Engines and Airframe Parts published in 1943. The exhaust valve alloys were similar to those used by the British, and the designs were also similar. The exhaust valve from the BMW 132K single row radial, which was apparently based on the Pratt and Whitney Hornet engine, was of the sodium cooled, hollow head type, with Stellite on the seats.]

Turning now to the cultural question, Dr Barton is quite right, there is a ‘cultural difference’, but not in the way one might think. In America, by 1925, they had realized that the aeroplane was here to stay. Instead of doing a three-day train trip between New York and San Francisco, it could be done in twelve hours, provided air travel was reliable. The US Government and various charitable organizations poured money into aircraft design and engine development. What they did not want, if you needed a reliable commercial service, were engines which need a lot of maintenance and valves needing regrinding every two or three days. So they went for the air-cooled radial engine, eliminating the need for water cooling. For valves, the low maintenance choice was two valves per cylinder, one inlet and one exhaust, initially relying on salt or sodium cooling to keep down valve temperatures.

Bryan Price: There was something which distinguished American from European designs. In the 1920s people who were designing aircraft engines were also designing for automotive use. Around 1923, the RAC introduced the taxation calculation that biased engines towards long stroke, small bore designs, which dominated UK automotive engine design for over forty years. Because of this there was a drive towards high-specific-output, liquid-cooled designs and this would push the use of four valves per cylinder for better breathing.

Something you have not mentioned is the mass of the valve and valve train dynamics, which was a big issue in the UK and Europe. But in the US, there was much more emphasis on low cost manufacturing, which was one reason why the Americans stuck with air cooling for so long and two valves. In addition they had cheaper fuels and were less concerned about having more fuel-efficient engines. In consequence the Americans went for big bore, large capacity engines of limited output.

Author: My impression is that in terms of bhp per litre, American car engines used to be very poor. However, US car manufacturers introduced overhead valves much earlier than UK engine constructors. The reason for this comes back to the manufacturing issue, and here my opinion differs. In Britain we had to build cheap engines and the side valve was ideal. So we will have to differ on this point.

Bryan Price: Okay. But the first four-valve overhead-cam engines were those from Peugeot in 1914, and engines of this type were being used in Grand Prix and higher output engines.

On the German question the biggest competitor to the Merlin was the DB 601. This differed from the Merlin in having fuel injection.

Dave Andrews: Aircraft engines used to have water injection for take-off. What was the thinking behind this? Was the injection into the cylinders to keep the valves cool?

Author: I would ask Clive Ellam, who is from the aircraft industry, if he could comment on the water injection issue.

Clive Ellam: There is a mystery about the effects of water injection, but on Rolls-Royce engines the water was injected into the eye of the supercharger impeller. It then vaporized and the two theories were either that the cooling increased the mass of the charge, or it cooled the mass of the charge so that the volumetric efficiency was increased. I do not know any one who injected water directly into the cylinders.

John Russell: There is a discussion in technical press about how much Formula One contributes to engine design. Have you got any evidence, whether what is going on at Goodwood and elsewhere, that competition was improving our knowledge and performance of engines and valves?

Bryan Price: With respect to Formula One, the main developments have been made in the area of materials, where they have been given the opportunity to prove themselves. For example, the ‘turbo era’ of racing cars had encouraged the turbocharging of production cars. Today, there are efforts to develop KERT (Kinetic Energy Recovery Technology), which will be incorporated into hybrid vehicles.

Author: At present the F1 rules seem to be hindering development. Engine speed is limited to 18,000 rpm and there is a minimum weight limit. The rules therefore are inhibiting the use of light-weight/high-strength materials. For example, if we consider a valve being pushed up and down at 18,000 times a minute, plus the rest of the valve train, one is expending a huge amount of energy, so lightweight valves could make a real contribution to engine power. Even with normal vehicles, on the motorway, where the engine speed is moderate, the power required to drive the valve train is a significant fraction of the engine output.

Ed Marshall: Fred, you have given us an extremely entertaining evening of just short of a hundred years of exhaust valves. It seems that it was really a case of the need to survive (improvements in engine output) which was at the back of valve development.

I liked your description of Ricardo, Heron and Midgley as representing ‘The Good, The Bad and the Ugly’. But in 1920, ‘The Good’, Harry Ricardo, said that the exhaust valve had reached the limit of its development. Although Ricardo was not often wrong, he was really wrong about that! But I am not sure that Heron was that bad. [Author: Heron had a bad temper.] The oil companies had thrown high-octane fuels and tetraethyl lead at the valves, and Heron did a lot to get round that problem.

With respect to the German fuel situation, they hydrogenated brown coal, which gave them very a aromatic fuel, which has a high octane. They also had tetraethyl lead, so they had a fuel which was of the 90/130 grade, which was fairly good.

There is an interesting story about lead. When TEL was first manufactured, it was only made in the USA and then shipped to Europe. By the mid thirties, lead became quite common and was stipulated in aviation fuel specifications. The Air Ministry did recognize that in the event of hostilities, should America sign a neutrality agreement, there would be a problem. So after discussion with the Ethyl Corporation, and then with ICI, they set up a manufacturing base. To keep things on a level playing field, the Americans did the same in France and Germany.

Whilst the German plant was being constructed, the British found out, purely by chance, that the Germans were secretly building a second one! It was a case of a letter being put in a wrong bag. So at the beginning of the Second World War, the British knew the location of the two German plants. Now I would have thought that these would have been prime targets for the RAF, but they were never attacked at all. The plants went right through the War. At the end, the Russians dismantled them, toilets and all, and shipped them back to Russia.

I have one complaint! I did not hear the words ‘sleeve valve’, which of course ‘Mr Good’ put his money on in 1920.

I remember that back in the late 1960s, when we started taking lead out of gasoline, the first engine we tried was a Jaguar. On lead-free fuel, it ate the valves on just one tank of fuel. It was then a case of ‘Thank God for metallurgists’, since today we are now all using lead-free fuel.

Author: We should thank inventors, or God, since metallurgists still did not have a good theory to predict how materials wear.

Additional information

Notes on contributors

Fred Starr

F. Starr graduated in Metallurgy in 1966 and joined British Gas, becoming their principal investigator of steam reforming plants failures. From 1974 he ran a group to develop high temperature alloys for advanced coal and oil gasification processes. Some of this work is covered in his semi-historical survey ‘The Engineering Science of High Temperature Corrosion’, a lecture given at the University of Surrey. From the 1980s onwards he initiated programmes dealing with Stirling Engines, Closed Cycle and Inverted Cycle Gas Turbines, and the Rotary Vee two-stroke. After leaving British Gas, in 1996, his main work has been on power plant operation. His last formal job was with the European Commission’s Institute for Energy, where as a ‘Visiting Scientist’ he was responsible for the design of a plant to produce hydrogen and electricity from coal. In terms of industrial history, his focus is on steam, IC and gas turbine development, using modern knowledge to highlight the background to engine designs and breakthroughs. He achieved a life-long ambition in 2007 in gaining a doctorate with his thesis on ‘The Development of an Expert System for Failure Analysis of Power Plant Components’.