redictions regarding the DIFFERENT demise of the internal DIFFERENT combustion engine (ICE) have a long history. The steadily growing number of STROKES: hybrid and full electric ve- STROKES: hicles on the road has only added fuel to Pthe fire, so to speak. But while naysayers have been trying to decide how many more years the ICE has left, engineers INTERNALINTERNAL and visionaries at several different com- panies have been looking for ways to ex- tend its life well into the future. They’ve accomplished this by completely reimag- COMBUSTIONCOMBUSTION ining how an ICE works and what it looks like. In this article, we’ll examine the new technologies that have been developed ENGINESENGINES by these companies. Simple inline or V- type piston engines are definitely not in- cluded in this group. It’s anyone’s guess how many (or if any) of these designs STILL DELIVER will ever end up in a mass-produced ve- STILL DELIVER hicle that you’ll see in your shop. For BBYY KKARLARL SSEYFERTEYFERT now, it’s interesting to see how far you can go with air, a little bit of fuel and a TheThe growinggrowing numbernumber ofof alternativealternative great deal of ingenuity. EcoMotors International (www.eco powertrainpowertrain vehiclesvehicles maymay havehave youyou motors.com) has developed an opposed- thinkingthinking you’llyou’ll soonsoon bebe anan electricelectric piston, opposed-cylinder (OPOC) engine that will run on a number of different engineerengineer ratherrather thanthan aa technician.technician. FearFear fuels, including gasoline, diesel and ethanol. The original OPOC engine de- not.not. TheThe internalinternal combustioncombustion engineengine sign has a long history dating back to the isn’t ready to fade into obscurity. first decade of the last century, when it isn’t ready to fade into obscurity. powered French Gobron-Brillié passen- ger cars. The design was later used on Fairbanks Morse submarine and loco- engine—an external air-charger (super- than a traditional engine (more than one motive engines, Grey Marine and De- charger or turbocharger) forces air into horsepower per pound of engine weight). troit Diesel engines and German Junker the cylinder through ports in one side of This design configuration also elimi- aircraft engines during World War II. the cylinder sleeve. As the pistons move, nates the need for the cylinder head and The EcoMotors OPOC engine is a the ports are covered and the air is com- valvetrain components of conventional two-stroke, horizontally opposed, twin- pressed between the two converging pis- engines, offering a compact and simple bore, four-piston design. There are two tons. Fuel is directly injected and the mix core engine structure. In fact, there are pistons in each cylinder bore. The inner can be fired by spark or compression ig- 50% fewer parts than on a conventional set of pistons is directly attached to the nition, depending on the fuel used. Ex- engine. Due to the reciprocating action of crankshaft and they work in much the haust is eliminated through ports on the the pistons, all engine forces counteract same way as those in a traditional recip- other side of the cylinder bore when each other, for low noise and vibration. rocating-piston engine. The outside set they’re uncovered at the end of the pis- If more power is needed, additional of pistons is attached to the crankshaft ton travel. modules can be connected together, via long, titanium connecting rods that Because the combustion event occurs then separated at will via an electronic are tied to a bearing at the back of each in the middle of the cylinder bore be- clutch mechanism. This variable dis- piston. The outside pistons mirror the tween two movable pistons, there’s more placement feature allows power output motion of the inner pistons, moving to- surface area for the combustion pressure to be doubled when needed for larger ward the crankshaft as the inner pistons to affect. Consequently, more of the ener- vehicles, then decoupled when no longer move away from it. gy released by combustion is converted needed, to provide significant fuel sav- Intake and exhaust are handled simi- into mechanical force. This results in an ings. The manufacturer claims an engine larly to a conventional two-stroke diesel engine whose power density is higher family that is lighter, more efficient and 26 March 2013 The design is said to be compatible with most fuels, including gasoline, diesel, natural gas, propane and their bio- fuel replacements (e.g., ethanol). Addi- tional efficiency improvements can be achieved by incorporating variable valve timing, a variable compression ratio mechanism, direct injection and tur- bocharging, according to the manufactur- er. The company claims fuel-efficiency improvements of 30% to 50%. By closely controlling the thermal cycle, exhaust emissions are also claimed to be reduced. Achates Power (www.achatespower .com) has developed an opposed-piston, two-stroke diesel engine that uses two reciprocating pistons per cylinder. Like other opposed-piston designs, the Achates Power engine does not need cylinder heads, which are a major con- tributor to heat losses in conventional en- gines. Ports in the engine’s cylinder walls replace the poppet valves and friction- creating valvetrains of conventional en- gines. Intake ports at one end of the cylinder and exhaust ports at the other are activated by the piston motion and enable efficient air scavenging. The company claims its proprietary cylinder and piston designs achieve im- provements in combustion efficiency and oil consumption to meet the most stringent emissions regulations. In con- junction with the thermal efficiency ad- vantage inherent to opposed-piston en- gines, its designs are said to realize signif- Photoillustration: Harold Perry; images: EcoMotors Intl., Grail Engine Technologies, Doyle Rotary Engine & Thinkstock Rotary Doyle Engine Technologies, Intl., Grail EcoMotors images: Harold Perry; Photoillustration: icant reductions in fuel consumption economical than conventional engines, What’s different is the company has over conventional four-stroke compres- with lower exhaust emissions. taken this four-stroke, spark-ignited (SI), sion ignition engines. The use of two- Pinnacle Engines (www.pinnacle- opposed-piston, sleeve-valve architecture stroke compression ignition will permit engines.com) has taken a different ap- and added something called the Cleeves the use of second-generation renewable proach to the opposed-piston (OP) en- cycle, named for Monty Cleeves, the fuels derived from soybeans, biomass, al- gine design. Paired pistons facing each company’s founder and chief technical gae and other sources. other inside common cylinders are still officer. Control of the engine’s sleeve The Scuderi Group (www.scuderi utilized, but there are two crankshafts in- valve allows the engine to provide Otto group.com) has developed an engine us- stead of one. They’re on the outside of cycle combustion (constant volume com- ing a split-cycle design that divides the the horizontally opposed engine layout, bustion) or diesel cycle combustion (con- four strokes of the combustion cycle be- and drive the paired pistons toward each stant pressure combustion), depending tween two cylinders. One cylinder han- other in unison. The two crankshafts are on operating conditions and the fuel dles the intake and compression strokes linked to each other to keep everything available. (the compressor cylinder), while the oth- synchronized. In addition to eliminating the need for er is responsible for the power and ex- Like the EcoMotors OPOC engine, conventional valve gear, half the total haust strokes (the expander cylinder). Pinnacle Engines’ OP design does not number of ignition and injection compo- By splitting the four strokes between require a cylinder head or valve gear. nents are required compared to a con- the two cylinders, the engine is able to And like many things automotive, if you ventional boxer engine, because two pis- produce one combustion cycle per crank- look back far enough, you’ll discover that tons share a common bore. The engine’s shaft revolution, just like a two-stroke en- this design has been tried before (World modular design is easily scalable, de- gine. Also, by separating the compression War II aircraft engines). pending on the required power output. cylinder from the power cylinder, the size March 2013 27 INTERNAL COMBUSTION ENGINES STILL DELIVER of the compressor cylinder can be re- duced to eliminate some of the negative work of the compression stroke. The en- gine’s output is the difference between the positive work produced by the power stroke and the negative work consumed during the rest of the cycle. An exhaust-driven turbocharger forces the maximum volume of air into the compressor cylinder. Once it’s been fur- ther compressed by the compressor pis- ton, the air is transferred between the paired cylinders via a crossover passage. Fully variable, outward-opening cross - over valves control the flow of com- pressed air from the first cylinder to the second. At the appropriate time, fuel can Illustration: EcoMotors International EcoMotors Illustration: be direct-injected into the expander Fig. 1 This cutaway illustration reveals the EcoMotors engine’s opposed-pis- cylinder or port-injected into the charge ton, opposed-cylinder design, which dispenses with the need for a cylinder head air during transfer into the expander and all of the related valve gear. The extra-long pair of connecting rods allow cylinder via the crossover passage. the outer pistons to mirror the movement of the inner pistons. As the compressed air is transferred to the expander cylinder from the crossover before the piston reached its bottom pander cylinder. By differentially sizing passage, sonic flow and high turbulence dead center (BDC) position. The early the cylinders, IVC is timed at a period of enhance fuel/air mixing and promote sta- timing strategy effectively shortened the low piston velocity, where an optimum ble, robust combustion.