Among projects undertaken by Paxman's Experimental Department during the 1950s was some development work on prototype gas engines. From surviving records of what became the Development Department it is known that trials were carried out with at least four diesel engines which were converted to run on gas. These experimental engines were modified versions of three types in the Paxman range: the RW, RPH and YH. Technical details of the original diesel versions can be found on the page Paxman Engines since 1934.
It is not known what prompted the Company to start looking again at gas engines in the early 1950s. Paxman had designed gas engines and built them in large numbers earlier in its history but that business dried up during the 1930s. During the 1950s the Company was supplying rotary vacuum filters to sewage works for dewatering sludge so perhaps this triggered thoughts of the potential for using sewage gas as an engine fuel.
The first report in the Development Department's gas engine file is about the testing in August 1951 of a 4RW running exclusively on gas with spark ignition, then in dual fuel mode with butane and then methane.
The following report, dated March 1952, is on tests of one bank of a V6 RPH in dual-fuel mode.
The next report covers the first 500 hours running of a prototype 6YHG (67G) spark ignition gas engine installed as part of a free-standing alternator set at Colchester Sewage Works. This report is dated June 1955 and also mentions a single cylinder gas test engine. Trials on the modified 6YH continued for over two years. To 14th September 1956 the '6YHG Prototype Spark Ignition Gas Engine' at Colchester Sewage Works had completed 1,750 hours. Report EX334/10 states: 'The general policy with this engine was to keep it running either on loop tests or continuous approximately steady loads supplying power to the Sewage Works, when the speed was limited to 1,000 rpm 50 cycles.'. The Gas Engine file ends with EX334/11 in August 1957, reporting on alternative carburettor tests on the Sewage Works engine.
In addition to the above there are reports on trials with a modified 12 cylinder YH engine. The first, dated December 1955, gives details of a Sewage Works test installation of a 12YHG gas engine, a cast iron engine with aluminium alloy cylinder heads, direct coupled to a BTH 330 kVA 1,000 rpm alternator. This engine was subsequently painted and despatched to Shell's Stanlow Refinery on August 23rd 1956 and was running on September 24th. The power was absorbed in a load tank so John Benham thinks this must have been a mutual research project rather than anything commercial. An October 1956 report on the Stanlow engine quotes total running hours as 700.
The gas engine reports from 1955 on are by A J (Joe) Ellis, Research and Development Department countersigned by Roy Dingle or John Stent. The earlier work was by K (Ken) W Allen, Experimental Department, countersigned by D M Pearce, Chief Experimental Engineer.
Roy Dingle was later responsible for leading the design of Paxman's Ventura (YJ) and Valenta (Y3J) engines and became the Company's Chief Engineer. John Stent continued to work on diesel engine design at Paxman until retiring in 1989. David Pearce worked for the Company for 18 years before leaving in May 1964, at which time he was Chief Engineering & Sales Executive with Regulateurs Europa. Another of the experimental projects David Pearce worked on during the 1950s was the development of Paxman's Hi-Dyne engine.
We are not aware of Paxman subsequently putting any gas engines into production although this must have been under serious consideration at one time. The Company did go so far as to produce a gas engine brochure. Paxman publication no 1517, entitled Paxman Gas Engines, is dated November 1956 and features the 6, 12 and 16 cylinder YHG. Based on the YH engine (with the G suffix indicating Gas), the quoted power outputs ranged from 180 to 667 bhp, with speeds of 900, 1,000, 1,200 and 1,250 rpm. The brochure referred to the increasing availability of natural gas supplies in various parts of the world and demand calling for a high compression gas engine. The power output ratings were for dry gas at a standard compression ratio of 14.25 : 1. It has been suggested that such a high compression ratio would have given considerable problems unless the fuel was of high quality with no impurities. The brochure describes the engines as being fitted with two high tension magnetos, one for each bank, mounted vertically in a bevel gearbox fitted in place of the fuel injection pumps. Two point sparking plugs were specified and the engines were claimed to be suitable for operating on "dry" gases (methane or ethane) or washed and unwashed sludge gas.
Significant modifications required when converting a diesel engine for running on gas include:
John Cove's Recollections
John Cove emailed me in December 2014 with his recollections of the 12YH engine converted to run on gas. He was unable to comment on the experimental work on gas engines done in the early 1950s as until 1956 he was working either in the Service Department or as Quality Engineer so played no part in this development work. However, when finally the 12YHA was converted to run on gas he did take more interest. Everyone was very interested in a new engine design which might have become part of Paxman's commercial range and he well remembered seeing this engine on the test bed.
Initially, in the first stages of design, it was thought that there would be one 'carburettor' (* see note below) per bank of cylinders. Then it became apparent that the inlet manifolds, running the length of the engine each side after the carburettor, would each have a pretty large volume and this volume would be filled with a highly explosive gas/air mixture, with the risk that any spark or hot spot would result in a serious explosion. Moreover the gas would still be there when the engine was stopped and would have to be carefully removed before any maintenance work could commence. All this was deemed to be an unacceptable risk. The solution was to give each of the twelve cylinders its own individual carburettor, mounted right onto the inlet port. When John saw the engine on test this was the arrangement being used.
The risk of explosion was thereby reduced but at the cost of a very complicated control linkage and twelve quite large carburettors which made it hard to tune the engine so that each cylinder was doing an equal share of work. John did not think that the cost implications were looked into at that stage at all but the engine did run a number of hours at Stanlow with that setup. He commented that certainly the running at Stanlow was a mutual research project rather than a commercial venture. He had never seen any report so did not know how well it went or if any problems were met with.
Although publication 1517 might have listed other sizes of YHG engines, all work terminated after the Stanlow trials and John thought this was for a combination of reasons, even discounting the possibility that the Stanlow test may have revealed some additional problems.
He says this was a very complicated machine to offer to places where gas was plentiful but people with the skill to operate such an engine and keep it in tune were unlikely to be found. Furthermore gas-rich places would require even more power than the YH range could provide and this would be more easily provided by a gas turbine which is an inherently simpler machine capable of much higher outputs. Here it must be remembered that at about this time the 'Ruston Gas Turbines' division was being set up and was thought to be the way forward for the Group to offer power units that could utilise gas that would otherwise be wasted. So Paxman left the gas-burning power unit market to Ruston which made a great success of its gas turbine business.
* NOTE: John commented that some people might contend that a gas engine does not have a 'carburettor' because no liquid fuel to be vapourised and mixed with air so, in reality, a gas engine has just a 'mixing valve'. He added that within Paxman at that time staff certainly did not talk about 'mixing valves' when discussing this engine. He was pretty sure they used the term 'carburettor' which he considered gives a better insight into its actual function in a gas engine.
Acknowledgements: My thanks to John Benham, Senior Product Engineer, MAN Diesel Ltd, who extracted information from Paxman's surviving engine development records, to Alex Walford who advised on various points relating to gas engines, and to John Cove for his recollections.
© Richard Carr 2007 and 2014.
Page updated: 11 DEC 2014