FOUR-STROKE ENGINES
FIRST COMMERCIAL RCCI INSTALLATION GOES LIVE
Image: Deen Shipping
The subject of many test-bench projects has broken out of the lab, writes Stevie Knight
Deen Shipping’s MTS Argonon is a fairly ordinary-looking 6,100dwt bunker tanker. But beneath its placid exterior, beats a long-awaited world first: a commercial, reactively controlled compression ignition (RCCI) engine. So, what could have prompted a pragmatic carrier to risk a perfectly serviceable, Caterpillar 3512 engine in order to explore something so exotic? In fact, there are a couple of very good reasons: one is fuel flexibility, another is emission regulation. And then there’s also efficiency. In a standard engine quite a lot of energy goes missing during the power stroke, whether that’s spark or diesel ignition. It’s a fairly simple mechanical issue centring on crank angle: at what point in the cycle the combustion delivers its main thrust. Ideally “what you want is all the fuel burnt at once, at around top-dead-centre (TDC), then you have the highest efficiency; no ignition before that point, and no delay”, says Paul Nooijen of ArenaRed, the innovation company behind the RCCI solution. However, SI engines can spark as much as 40 degrees before TDC, and most of the fuel is actually burned some way after, 10% lagging till plus-90 degrees. “You lose twice: not just all the pressure build-up before TDC, but also the fuel that comes late into the combustion,” says Nooijen. “Diesel is more efficient, ignition tends to start at its earliest 20 degrees before TDC, and by 70 degrees after TDC it’s usually burned 90% of the fuel in the chamber.” But both could do better, with a little help. Therefore, ArenaRed’s RCCI retrofit completes the whole process, from ignition to combustion, in a short, 23 degree
14 | OCTOBER 2020
8 The MTS Argonon has been successfully adapted to run in RCCI mode, allowing the tanker future fuel flexibility as well as cleaner, more efficient operation. Inset: The neat ArenaRed RCCI retrofit is fairly small but effective for its size
crank arc. So, what does this fairly small bit of kit actually do that enables an engine to radically alter its behaviour? “The RCCI works by taking a low reactivity fuel, whether that’s hydrogen, gasoline, methanol, ethanol or propane, and bringing it into the combustion chamber via a very simple port fuel injector,” he explains: this happens across the entire intake stroke, giving it plenty of time to mix with the incoming air. In the case of the Argonon, “the main fuel is LNG” he says. Then 1% diesel is added via a special injection head, but not as a trigger for the classic, dual-fuel pilot ignition. “Instead, you bring in this small amount of diesel at around 100 degrees before TDC, this gives it enough time to move completely into its gas phase,” says Nooijen. “This is important, because if you work on a diesel principle, you inject the fuel at a very high pressure to optimise atomisation... but you are still talking about droplets, which form NOx on the outside and soot on the inside during combustion.” It is only when the piston rises to just before TDC that this now homogenous charge ignites, and it does so fairly promptly. According to Nooijen, “You have ignition three degrees before TDC, and its combusted 90% of the fuel by 20 degrees after TDC.” Interestingly, the lack of an advancing flame front reduces thermal stresses, lowers heat loss from the exhaust, and the very complete burn also mitigates methane slip. Together, hitting the right point on the crank angle, avoiding NOx generating hotspots and cold areas of unburned hydrocarbons means an RCCI retrofit can deliver up to around a third more power, at the same time as gaining another 10% in sheer efficiency. And it doesn’t need expensive after-treatment either, ditching the SCR.
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