ANOTHER COOL ENGINE

April 27, 2011 Vol. 7, No. 9

Last time out I teased a bit with brief mention of another new engine design, the very intriguing Scuderi split-cycle engine, yet one more variation on the internal-combustion theme. Lord knows how many there have been in the last century and a bit, though I do know the number’s not small. Few of them have had mainstream success over the years, but it’s the nature of the creative engineering mind to keep trying. To seize an idea and run with it as long as the money holds out.

I’ll get to the Scuderi in a sec.

There’s been a spate of news lately about what seem like radical new engine ideas, and for a while it felt like I had an e-mail message every day asking if I wanted to know more about breakthrough Engine X. I’m exaggerating, of course, but the truth is, I’ve heard about more such innovations in just the last two or three months than in my previous 32-plus years of writing about trucks and sometimes cars.

Should I be surprised? Of course not, because fossil fuels are on the wane in some obvious respects even though they actually remain quite plentiful. With both fuel-cost and environmental pressures relentlessly beating conventional engines about the head — justifiably or not — there’s a strong imperative to develop internal-combustion motors that consume substantially less fuel while creating sharply fewer nasty emissions and coming in smaller, lighter packages.

The main alternatives — electric power sort of now for some applications, the hydrogen fuel cell still off in the distant future — don’t really cut it across the board. The diesel/electric or diesel/hydraulic hybrids are great, very effective in some parts of our truck world, but they don’t fit every job and won’t reach true commercial viability for a few years yet.

There’s more promise on the fuel front, I think, from things like algae-based biodiesel, from methane captured at landfill sites, from many other sources synthetic and otherwise. In the short term we have natural gas, of course, which is surging toward the forefront at some speed and has the very enticing virtue of being plentiful. Options like these won’t come cheap, sad to say, but we may not have — or may not be offered — a choice in the matter.

I don’t mean to slight present-day diesel engines here, I’m keen to point out. They’re models of largely unrivalled efficiency. And I’d venture a guess that a big-bore 2011 diesel would be 30-50% more stingy in terms of fuel consumption than it was in 2002 if all the engineers and chemists employed to reduce its emissions over this last decade had instead been tasked mainly with trimming fuel use. Ah, but that’s another argument for another day.

The new fuels I’m talking about, fossil-based or not, can certainly be used in conventional diesels, though sometimes requiring expensive modifications. And they will be.

Those fuels are also viable in the new crop of engines hoping to break into commercial use, like the two-stroke EcoMotors OPOC that Navistar is helping to develop. I joked that it could run on anything except charcoal briquettes when I first wrote about it a few weeks ago (March 2).. That acronym stands for ‘opposed piston/opposed cylinder’ and the engine promises two to three times the power density of conventional engines with 50% fewer parts and at least 15% better fuel efficiency. Its small size would bring truck designs that could better exploit aerodynamic potential.

It’s sort of a cross between the flat-four VW motor of years gone by and various Junkers aircraft engines that propelled a lot of German planes starting in 1929. The Junkers Jumo 104 variant — some call the Jumo the most famous engine in diesel aviation history — had six cylinders and twelve pistons in an opposed-piston configuration with two crankshafts, one at the bottom of the cylinder block and the other at the top, geared together. The pistons moved towards each other during the operating cycle and essentially formed two cylinder heads as they met. The OPOC is a variation on that theme.

There’s actually another broadly similar motor on the scene now, and it too can be compared to that old Jumo. In fact the company — Achates Power — says its engines are inspired by that same Junkers Jumo. Founded in 2004, Achates says its engine can comply with both EPA10 and Euro6 emissions standards. Like the OPOC, it eliminates the cylinder head and valve train, which reduces heat and friction losses, has fewer components, uses fewer raw materials, saves weight and has a smaller displacement.

San Diego-based Achates claims its engine reduces fuel consumption by nearly 50% compared to a comparable gasoline engine and by 10-15% compared to a traditional diesel. The company says it has fully functioning prototypes with more than 1000 test hours, as well as "leading edge" testing, simulation and analysis tools.

OK, SO WHAT ABOUT THE SCUDERI? Well, start thinking Miller cycle, which leaves the intake valve open longer than in the conventional four-stroke ‘Otto’ cycle engine that we know and love. You end up with what’s almost a fifth stroke because the compression stroke really happens in two cycles. A Miller cycle engine needs a supercharger, I believe.

Scuderi Group boss Sal Scuderi calls his ‘Split Cycle’ variation on that theme "the perfect Miller-cycle engine", though there’s no fifth stroke, and earlier this month he presented two technical papers on his split-cycle motor and its valve-control system at the SAE Congress in Detroit. His company hails from West Springfield, Mass., a seemingly well funded engine development outfit that’s intent on re-engineering the conventional four-stroke engine. Its global patent portfolio contains more than 476 patent applications filed and 154 issued in 50 countries.