COVER STORY


eff iciency. Also there’s no auxiliary drive belts on the front, so items such as the water pump are driven by a 48V electric system. We also fi tted low friction bearings throughout.” Around 59 per cent of the weight


of the engine has been reduced. This was achieved by large improvements such as redesigning the cranks, counterweights and gears, as well as smaller improvements like further use of plastic for items such as oil pans. Burek explains, “The biggest single weight reduction concerns the cylinder block, so instead of an iron block with wet liners we used a mass production automotive- style aluminium block with spray bore liners. This reduced the weight of that component by 66 per cent.” It turned out to be one of the most


complex castings he has ever been involved with. “With no head gasket to control coolant fl ow, this is done by cast passages in the engine itself. Getting the right balance took thousands of hours of CFD.” Huge amounts of modelling was done on the project, from air path


The ‘delta’ triangular arrangement


Delta force


The OP confi guration does have form when it comes to unusual engines. Take the Napier Deltic, for example. Introduced after WW2, the engine powered trains and boats in diff erent formats for six decades. Nigel Paine, editor of Napier Heritage News is currently writing a book on the subject. He says, “The Deltic engines had an excellent power-to-weight ratio meaning they could power high-speed craft such as motor torpedo boats without the extra weight and size of engines of similar power. Having a triangular design utilising an opposed piston concept meant there was no need for heavy cylinder


heads. The body of the engine was made of cast aluminium and held together by steel tie bolts to take the engine forces. This meant that the bulk of the engine was non-ferrous, making it ideal for use in minesweepers. Deltics were fi tted in Royal Navy Ton and Hunt Class minesweepers and mine hunters and were used for over 60 years, far longer than any other prime mover.” The engines also utilised the


concept of repair by replacement which increased the overall availability of the vessels and railway locos they were fi tted to. A mixed blessing, as any job larger than an injector


change would require removal of the engine. Paine adds, “They were designed for the Royal Navy and so were treated well. British Rail had a love/hate relationship when fi tted to locomotives. They were very much pampered racehorses compared to other trains. However, they had amazing service availability – just 22 Deltic locomotives replaced 55 Pacifi c steam locomotives on the London to Edinburgh run.” After 20 years of service, the locos were withdrawn and replaced by faster InterCity125 trains.


CFD to optimising scavenging and reducing restrictions to the structural FEA including thermal, fatigue and bore distortion, making sure the piston rings would seal well.


UNDER TEST Nick Fortino is Ricardo’s Project Leader responsible for the test phase. He says, “Despite knock-on eff ects of the supply chain issues caused by Covid, we managed to get the testing done. Getting all these diff erent complicated technologies like the eturbo, EGR pump, and the various actuators to work together was a challenge. To test, we took 11 steady-state test points covering high frequency portions of the FTP cycle to validate emissions and fuel consumption, with the targets set by a 1D simulation. The fuel consumption side was relatively straightforward, but emissions required more thought.” This was due to relatively


cool exhaust gases. “The EGR doesn’t help here,” continues Fortino. “We solved the problem by placing two oxidation catalyst bricks in the


manifold upstream of the turbo, as close to the engine as possible to minimise time to light-off . Downstream of the


❝While modern


four-stroke engines can now surpass OP power density, the fact remains that OP can be very fuel eff icient due to the reduced heat transfer.


turbine, there is an electrical exhaust heater, an additional oxidation catalyst, and a SCR system.” With the desired performance


improvements met, the engine has been returned to Achates for further examination. Perhaps these improvements will be enough to see OP engines fi nally gain a greater market share.


For more information visit www.achatespower.com and www.Ricardo.com. For more about Napier, visit www.npht.org


www.engineerlive.com


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