Having burst a 30,000 psi fuel line early in the 2,200 nautical mile leg from Hawaii to the Marshall Islands, it’s been a tough leg for the Earthrace crew as they are depending on just one of their two Cummins engines. They are now a tantalising 180 miles from Majuro where the Cummins engineers are waiting to fit the new fuel line.
At 12:35 GMT Earhtrace had covered 11,971 nautical miles, so they are half way around the world. In the last 24 hours they have travelled 359 miles at an average of 15 knots and they are still 2,111 miles ahead of the Cable & Wireless record pace as Skipper Pete Bethune pulls every last horse from his remaining engine.
Maintaining the 78 foot trimaran's speed at 15 knots is at the outer limit for the single 540-horse power Cummins engine. The Earthrace engines are brand new, state of the art computer controlled versions of the successful QSC range of Cummins engines. The engines are turbo charged, intercooled, and have the new common rail injection system. They represent the height of high efficiency diesel technology and for many this is what the race is all about, as they are proving that massive reductions in fuel consumption are possible with the latest technology.
For the manufacturer of diesel engines for example, these high publicity records are a clear statement that once again 'we' produce the best engine that money can buy. I say 'once again' because Cummins engines were in the Cable & Wireless boat that holds the current round the world speedboat record. Cummins also produced the engine in the world's fastest diesel pickup truck at a blistering speed of over 222 mph. http://www.bankspower.com/sidewinder.cfm
Two factors combine to build the world's top diesel engine. They are longevity and weight. The challenge is to pack more horsepower into a smaller lighter package and make it last a reasonable amount of time. In order to understand how engine designers pack extra horsepower into a small space we need a quick review of how a diesel engine works.
Diesel is not particularly flammable so to make it burn we need to blown air at the flame. It's a lot like blowing air at a wood fire to get it started. To make our engine go faster we pour more diesels into the fire and blow in more air. Designers really want the fires to roar so they pour in even more diesel, but this time something different happens. The fire begins to smoke because we can't supply any more air into the blaze. This is exactly what is happening when we see a big truck climbing up a long hill blowing black smoke.
The designer needs more air to make a bigger fire in the small firebox so he builds a big fan like pump called a turbo, and blows a strong column of air at the fire. The fire should roar, but it does not because in pumping the air to blow at the fire the air got hot. Hot air expands so were blowing pressurized, but thinned air at the fire.
Again the designer is at work to build a system to cool the air thus shrinking it so he can force every last oxygen molecule into the fire. This air cooler is called the after-cooler or inter-cooler. To most people familiar with diesel engines they have heard the terms turbo charged and inter-cooled forever. This was the height of technology, until just a few years ago.
Engineers had perfected the injection of air, but they still had one problem. The diesel sprayed into the fire was not fine enough. Not all the diesel burned. A small amount of fuel was still burning after leaving the firebox thus wasting energy.
The fuel spray had to be made more into a finer mist, and the only way to do that was to pump it harder. Since diesel fuel was already being injected at over a 1,000 psi the designers had a complex job ahead of them. They needed to raise the injection pressure from 1,000 to 30,000 psi. At this extreme pressure diesel fuel would atomize into an almost perfect burn pattern, decreasing fuel waste significantly.
Building the high-pressure pump was the easy part. Finding a quick acting high-pressure valve that could reliably open and close over a thousand times a minute was the stumbling block. The answer was found in high-speed electronic valves controlled by a sophisticated computer monitoring system. Common rail injection was born and is often called the first major design improvement in the diesel engines since it origin over a hundred years ago.
And that is what the engine manufacturer is proving in this race. They have the best fire box (cylinder) and the best air stream (turbo charger). It shows they have the best ability to cool the air stream (inter-cooler) and the finest injection system. Combined, these improvements are now called a turbo charged, inter-cooled, common rail injected marine diesel engine, and that is the diesel engine system that powers Earthrace today.
In our next update Scott Fratcher will explain how the big Cummins diesel engines are laid out inside Earthrace and why the engine mounts are not breaking like in the last race.
Meanwhile Earthrace is just 15 hours from the Marshall Islands as Pete Bethune and his crew listen carefully, hoping their remaining engine will not miss a beat.
Go to Scott’s website to see his Earthrace Books at www.yachtwork.com