Automated digital design delivers RR Allen 500023 April 1998
A completely new marque of large medium speed four-stroke diesel engines has been introduced to extend the top end of the range of Rolls Royce Allen's own diesel designs. Covering an output range from 3 to 10 MW, the new Allen 5000 benefits from state of the art engine design techniques applied through partnerships with Ricardo, and Perkins on combustion optimisation. The application of these technologies has achieved a new order of efficiency, economy and reliability. The new engine is described by Rolls-Royce Allen as the most powerful medium speed diesel engine range available today for its size.
Awe inspiring panache, dazzling laser light displays and ear bursting multimedia made the introduction of the new Rolls-Royce Allen 5000 diesel engine range a memorable event. Does the new product, developed by the former Allen Diesels under the new Rolls-Royce - Ricardo partnership, really live up to all the hype? It may be the most important new product introduction in the revamped, redesignated and upgraded Allen Diesel engine range since the Rolls-Royce takeover, but they did not risk running the engine and letting the visitors climb over it in the time honoured fashion.
The new engine has been conciously developed and designed for the growing IPP power generation markets, mostly in the emerging economies around the world. The under 10 MW generating set market in the vast regions of South East Asia and parts of China have not been greatly diminished by the recent currency exchange crises, in some parts demand for local power plants has increased as the prospects for network extension recede into the distance.
As stressed by the Director of Diesels Peter Dobbs, the engine has been devised to meet what the market wants to buy, not what the engineers think they ought to want – an ironic sideswipe at the designers since the main emphasis of the presentation stressed the commitment to exploiting the most advanced design technology resources available to produce what Engineering Director Glyn Youdan described as "A market leading design".
The new engine
Designed to develop half a megawatt per cylinder for an engine output range from 3 to 10 MW, the Allen 5000 fills in something of a potential gap in the broad spectrum of Rolls-Royce engines between the smaller well established Allen engines and the joint venture licenced products with MTU, Pielstick. Beyond the 16 MW output of the Niigata 46, the range of outputs is neatly extended by the Rolls-Royce gas turbine prime movers up to the 50 MW industrial Trent.
What visitors to the grand introduction saw was the first engine built, all clean and gleaming with silver paint and polished metalwork. This engine is apparently destined for the first field test site which has been contracted. A second 12 cylinder machine is already in operation and a V16 machine is currently being built.
The medium speed four-stroke engine has a design thermal efficiency of around 45 per cent running at the synchronous speed of 750 r/min burning HFO or distillate. The favoured benchmark for engine development comparison seems, rightly or wrongly, to be the bmep, which in this case is claimed to be ten per cent higher than Allen's competitors at 30 bar.
The emphasis on advanced engine design techniques certainly seems to have resulted in a remarkably short development schedule, and this itself yields to a substantial saving in investment. In the spring of 1995, a preprotype research engine, designated the Allen 4006+, was built. By September 1997, a power output of 333 kWb/cylinder had been demonstrated. This was increased to 400 kWb/cylinder by October 1997, and the target of 525 kWb/cylinder was reached in January 1998. Development operation running on distillate and HFO was put at 1000 hours to date.
The design specification targets for satisfying the marketing specification for the concept design phase were put at:720/750 r/min engine 1 MW per cylinder pair 320 mm cylinder bore 410 mm stroke 5 bar turbocharging potential market leading fuel injection equipment with digital technology 30 bar bmep low cost per kW.
More generally, the development of a customer focused product was stated to be based on a marketing specification designed for:maximum reliability minimum captial cost market leading fuel consumption maret leading through-life costs emissions control to meet future international legislation.
The designers have achieved a 35 per cent reduction in components and simplified many other facets to improve accessibility and to extend component life and durability.
The cutaway view of the engine reveals a familiar state of the art medium speed four-stroke engine configuration. The underslung crankcase, which is made from spheroidal graphite cast iron, incorporates cast in integral air, oil and water passages. Four stud cylinder head castings are of compacted graphite (vermiculite) iron to give optimum strength and thermal conductivity.
A three piece connecting rod design makes for ease of piston removal and servicing. All of the main fasteners are designed specifically for hydraulic tensioning. Unusually high capacity cooling channels are provided around the valve seats. The composite pistons, which have a special steel crown and iron skirt, are designed for a mean piston speed of 10.25 m/s at 750 r/min. The camshaft is of segmented design to allow side removal of discrete sections.
The induction and exhaust manifolds are notably compact. The advanced single entry turbochargers have axial flow turbines in uncooled cases with a view to providing 5 bar induction pressure. The 30 bar bmep is achieved with maximum pressure of 210 bar.
A major factor in reaching very high efficiency figures across a wide range of engine load is the new approach to digital fuel injection control jointly developed by Allen Diesels and Bosch. A servo controlled solenoid controls injection on the basis of the real time calibration of each cylinder for optimum performance and minimum emissions.
A major factor in the development of such advanced engine performance in such a short time schedule has been the use of computerized analysis and design tools to a further extent than has been used before. This expertise has been developed by a multi-disciplinary design team built up since the creation of the Allen Diesels' diesel research and development centre located in Bedford, UK in 1994.
The team brings together Rolls-Royce design engineers and Ricardo analysts supported by Ricardo software and Silicon Graphics computer systems in a common electronic product strategy developments regime. Component strength, performance and reliability have been progressively enhanced through evaluation of the static and dynamic behaviour of critical parts in terms of thermal and structural characteristics.
Three dimensional cooling strategy development for the cylinder liner and cylinder head geometries were critical in the definitive design phase. Water flow velocities ranging from 1 to 3 m/s were designated for the most difficult temperature control areas including exhaust valve seats. Much use of digitally analysed finite element analysis was equally vital for the development of the crankcase design and cylinder head thermal analysis.
Using the increasingly popular Pro-Engineer 3D CAD system, the software will respond to component design changes by automatically updating and modifying the design parameters of all the associated components.
Magnasoft software is used to model the solidification of mould material during the casting process to optimise the characteristics of key component castings. This was particularly beneficial for the cylinder head casting design, in which the casting process had to be modelled with and without the presence of the feeder system for comparison.
Combustion process CFD studies in which temperature profiles and NOx generation profiles were accurately modelled for the definitive design phase used extended development of succesful software developed in cooperation with the Perkins specialists.
A selection of such key data were fed into an engine specific WAVE cycle simulation model which was used for performance prediction.
Having identified the worldwide market drivers in terms of what the independent power producers (IPPs) are demanding for their generating plant prime movers, the company has set about providing the kind of product support required to service this key market.
The company claims a comprehensive customer care programme to fit individual project needs including tailored maintenance contracts, efficient spares supply, repair and overhaul and customer training through the international network of Rolls-Royce service centres.
Twenty-four hour condition monitoring surveillance of critical parameters is also offered, either on site by the IPPs' own engineers, or remotely from the company's own control centre.
TablesTable 1. Allen 5000 output range under ISO 3046/1 1986 based on 97 per cent generator efficiences Table 2. IPPs’ demands give rise to four main product development drivers