Saving fuel is high on all of our agendas, but sometimes we overlook the obvious. This short blog examines the role of the Turbocharger Filter and offers independent evidence of why we should make serious efforts to keep turbochargers clean.
If you are serious about saving fuel you will know about the advances in hull form, advanced paint coatings, kort nozzles and air lubrication along the hull, all great ideas that work. Yet there is another fuel saver, right under everyone's nose, it's not sexy or cutting edge, it's not the latest innovative technology and it is used on all high speed engines - the air filter on the turbo-charger.
All engineers are aware of how important the turbocharger is in delivering ever increasing power to engines whilst searching for ever decreasing SFC. there is a great deal of discussion about turbo-nozzle and volute design, two-stage and in-series designs etc., yet little is talked about the air that flows through them.
The vast majority of low and medium speed marine engines have little more than a copper gauze to filter the air. At best these will stop a low flying seagull but will do little to block the real contaminates that stick like glue to internal surfaces, quickly negating some of the technical advances of today's turbocharger design.
It is interesting to note tat those operating a powerful Caterpillar or Cummins engine religiously monitor the air filters and change then as per the manufacturers recommended intervals. This is because the engine is supplied with the filters from new, owners would not dream of running the engine without the filter. Yet operators of medium speed engines continue to operate their engines drawing air from a polluted, oily exhaust leaking engine room, because their engine was not supplied a filter from new.
Where does all this oily polluted air end up? Against the first decent restriction it comes across - the charge air cooler. As the sticky oily air starts to coat the fins the air flow to the engine is restricted, so up goes the fuel consumption. We have all seen it I'm sure. Why else are coolers routinely removed for cleaning with evermore imaginative ultrasonic cleaning methods and chemicals to dissolve the encrusted mass that has worked it's way into the very core of the cooler? Interestingly Caterpillar and Cummins owners don't clean charge air coolers because they have a filter so maintain SFC.
Of course, many engineers acknowledge the problem so cove the air filter silencer with a filter cloth, better than nothing one would assume, but it can actually make the situation worse, why? The filter cloth quickly gets dirty and as it is the same surface area as the original mesh then it effectively starts to restrict the air floe, just like any blocked cooler but worse still as they are not very effective the cooler still gets ditry, so the engine now has two restrictions to the air flow.
One turbocharger manufacturer now has a design with pressure ratios of 6:1, unheard of a few years ago, yet filtration is still in the dark ages, why is this? Maybe it's not the responsibility of the turbocharger manufacturer? Supplying an air charge to a design required by the engine builder is their remit and adding filtration only increases the cost to the engine builder and intimately the end-user. In a competitive world build cost is key.
So what's the cost of a dirty turbocharger nozzle ring ot charge air cooler? If you refer to this excellent white paper from Wartsila, page 4 outlines a potential increase of up to 5g / Kwh. That's 3% on a 3MW engine on 180g / Kwh. Imagine a 3% fuel saving just by keeping things clean, most operators would jump at that sort of saving.
I remember clearly whilst on watch as a third engineer walking past a B&W 90GF when a turbocharger coughed due to restricted air cooler, WHOA ...... now THAT's a way to back flush a bit of wire gauze filter! ..... having best composed myself after thinking my world had just ended in a cloud of oily dust and dirt it left me thinking, why do we let the cooler get dirty for the sake of a simple filter?
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Peter Weide is MD of MarShip, a UK based company specializing in optimising the efficiency of marine diesel engines. Advising on maintaining the cleanliness of Air, Fuel and Lubricating oil, we regularly recommend solutions to operators and appear regularly in industry press, with our full range of diesel additives DieselAid we can offer solutions for most operating conditions and wont advise them if you don’t need them.