Later On

A blog written for those whose interests more or less match mine.

Extremely cool engine

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I particularly like that you can just add another engine if you need more power. David Welch and Mark Clothier write in Bloomberg Businessweek.

(click image to enlarge)

Retired Ford (F) engineer John Coletti got a call in 2007 from Vinod Khosla, the Silicon Valley venture capitalist. Khosla, co-founder of Sun Microsystems, wanted advice on a new engine technology in which he was considering investing. A mutual friend suggested he contact Coletti, who had served as the chief of Ford’s performance division. Coletti was skeptical that the design in question could deliver a promised 50 percent improvement in fuel economy. “Any time you hear about a new engine technology, you look for the Achilles’ heel,” the engineer said.

He pored over the EcoMotors International opposed-piston, opposed-cylinder (OPOC) engine. To his surprise, he concluded that it could perform as advertised. Coletti joined the company as president and chief operating officer in February 2008. Khosla and Microsoft (MSFT) founder Bill Gates were impressed, too, and together have invested $34 million in EcoMotors. They are attracted by a motor that, in theory, would allow a large pickup to achieve 27 miles per gallon. The company plans to license the technology to carmakers that would make their own OPOC engines, or manufacture and sell the engines through joint ventures.

Traditional engines have one piston per cylinder; EcoMotors’ version has two. The design saves space and weight, allowing for a 95-pound engine that is one-third the heft of a small, conventional four-cylinder motor and 15 percent to 19 percent more efficient. Designed by Peter Hofbauer, a former Volkswagen engineer and founder of EcoMotors, the small, modular engines can be hooked together to power autos of different sizes. A pair would yield a 150-horsepower motor suitable for a midsize car like a Toyota (TM) Camry. When the car is coasting, one of the engines shuts down, delivering a 50 percent boost in fuel economy. That’s a similar efficiency gain to what a hybrid gets, only EcoMotors says its model is less expensive. An OPOC engine will add roughly $600 to $900 to the cost of a vehicle, compared with an extra $3,000 for a hybrid, according to Don Runkle, chief executive officer of EcoMotors. Says Coletti: “This technology is disruptive to the industry.”

The question is …

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Written by LeisureGuy

30 July 2010 at 12:56 pm

One Response

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  1. Quote from an interview of CEO Don Runkle (of OPOC engine):
    “The OPOC is cheaper, better, simpler, stronger, lighter and cleaner than any other power generating technology now or in the foreseeable future. . .The engine’s width is exaggerated a bit . . .”

    Looking from a strictly technical viewpoint:

    The OPOC
    The two external pistons of the OPOC are the good ones. Their arrangement and lubrication is similar to those of the cross-head engines. A drawback is the necessarily long and heavy piston pin that extends well outside the cylinder. Another drawback is the two long and heavy connecting rods per external piston (about 2.5 times longer than the single connecting rod of the internal piston) and the increased number of crankpins and bearings.
    As compared to a piston performing a pure sinusoidal motion of the same stroke, the external piston of the OPOC moves more slowly around the Combustion Dead Center (CDC). This would improve the combustion efficiency, yet they come the internal pistons to spoil this advantage. The internal pistons of the OPOC move, around the CDC, more quickly than a piston performing a pure sinusoidal motion of the same stroke. Finally the volume between the two pistons and the cylinder increases, around the CDC, more quickly than in case of pistons performing pure sinusoidal motion.
    There is also a difficult lubrication issue with the internal pistons of the OPOC, especially the one thrusting over the exhaust ports. The hot cylinder with the exhaust port slots is where the piston skirt has to touch (to slide, to abut) in order to pass to the cylinder the thrust loads generated by the inclination of the connecting rod. The problem is that increasing the quantity of the oil at the exhaust port area of the cylinder, the oil consumption (it escapes at the exhaust) is also increased and the quality of the oil degrades sooner.
    In order to counterbalance the first order inertia forces and moments, the OPOC engine has to use internal and external pistons of the same reciprocating mass (it is the mass of the piston, of the piston pin and of the upper part of the connecting rod mass). Yet each internal piston has a small piston pin and a single short connecting rod, while each external piston has two long and heavy connecting rods and a big and heavy piston pin. The solution (?) is to add mass to the internal pistons. This increases the inertia loads and the friction loss. Besides, it is the offset between the two cylinders of the OPOC that generates a 2nd order unbalanced inertia moment. There is also a strong unbalanced inertia torque of 2nd order (just like in any four in-line conventional engine).
    The OPOC engine is so long (wide) because it is based on an opposed cylinder to counterbalance the inertia loads. Despite all this complication (four pistons, two short connecting rods, four long connecting rods, two cylinders) the “vibration-free” or “balance quality” of OPOC is not exceptional.
    Another issue is the different timing, during the scavenging, of the one cylinder as compared to the other: The cylinder that uses the internal piston to controls the exhaust ports aspirates differently than the cylinder that uses the external piston to control the exhaust ports. This asymmetry may be compensated at some revs and loads, yet it cannot at a wide rev and load range.
    The two long connecting rods at the sides of each cylinder are bridged at their small ends by a long pin (the wrist pin of the external piston) that makes the arrangement vulnerable to twisting of the external piston about its cylinder axis
    The lower side of each manifold communicates with the upper side of the same manifold through two narrow “channels” between the cylinder and the long connecting rods. As a result, most of the gas-flow happens through the upper ports of the cylinder (asymmetrical flow) and the scavenging scheme is something between the uniflow-scavenging and the loop-scavenging, which is another necessary compromise for the OPOC.
    Last, but not least, is the scavenging process, i.e. the most critical and power consuming process in a two-stroke engine. In the OPOC the scavenging is realized externally by a turbo-charger, not the ideal solution for engines that operate in a wide rev and load range.

    The OPRE
    Take now the OPOC engine, throw away the two internal pistons, throw away the four long connecting rods, throw away the two long and heavy piston pins and replace the unique multi-crank-pin crankshaft by a pair of single-crank-pin crankshafts located outside the pistons. What is left is the OPRE engine.
    The OPRE needs not long connecting rods neither an opposed cylinder to be “vibration-free”. And its width is more than 30% smaller than an OPOC of the same piston stroke.
    The combustion takes place at the slow dead center that provides a 30 to 40% additional time (as compared to the conventional engine) and a 20% additional time (as compared to the OPOC) to the fuel to get prepared and burned more efficiently. This extended piston dwell at the CDC allows a way higher rev range (it allows Direct Injection Diesels operating efficiently at 6000 rpm).
    If the one combustion per crank rotation is not adequate, additional OPRE modules can be added in series to make a multicylinder OPRE engine.
    By using the external side of the pistons (i.e. the wrist pin or cool side of the piston) as a “zero” cost, zero friction volumetric piston-type scavenging pump, the OPRE takes its final form. If the forced induction (turbo-charge) is desirable, it is OK for OPRE, because it can operate efficiently with and without turbo charging.
    The integrated volumetric scavenging pumps of OPRE allow the operation either with symmetrical timing or with asymmetrical timing between the intake and the exhaust.

    In the case of “divided load” applications, for instance when the OPRE is used as a range-extender with one electric generator on each crankshaft, its NVH properties are the best among the internal combustion engines (the Wankel rotary engine included). The OPRE range-extender is not only perfectly free of inertia vibrations, which is also true for the Wankel range-extenders, but it is also free from power pulses vibration on its mounds (supports) which is not the case for the Wankel range-extenders wherein each combustion into the Wankel rotary engine causes a reaction torque (power vibration) on its supports.

    Another “divided load” application of the OPRE is the Portable Flyer. With a couple of counter-rotating propellers the reliable, lightweight, efficient and true vibration-free OPRE makes a Portable Flyer (presented at http://www.pattakon.com/pattakonFly.htm ) that can change the world. Yet we have to fly first, to prove it.

    Despite what CEO Don Runkle claims, as compared to the OPOC engine the pattakon Opposed-piston-Pulling-Rod-Engine (OPRE engine) is: more compact, lighter, simpler, cheaper, is based on “built-in” scavenging pump of the piston type, has a wider rev range, is more vibration-free, provides additional time to the fuel to get prepared and burned more efficiently, has better lubrication, etc.

    For more (videos of the OPRE prototypes running on Diesel fuel,
    dimensions, weight etc): http://www.pattakon.com/pattakonOPRE.htm

    Thanks
    Manousos Pattakos

    Manousos Pattakos

    31 July 2010 at 4:10 am


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