Ecomotors Says Its OPOC Engine Could Deliver About 45% Greater Fuel Efficiency in a Class 8 Truck And With Tier 2 Bin 5 Emissions
|The EM100 base module showcased at the ARPA-E summit. Click to enlarge.|
EcoMotors International, a Khosla-funded startup working to commercialize an opoc (opposed-piston, opposed-cylinder) engine family (earlier post), showcased its EM100 (100mm cylinder bore) base module implementation at the ARPA-E Energy Innovation Summit in Washington DC last week.
With a two-module application configured at the appropriate power level (to deliver a combined 480 hp), the opoc unit could deliver about 45% better fuel efficiency compared to a conventional heavy-duty diesel engine in a Class 8 truck, the company suggests, while delivering emissions at the US Tier 2 Bin 5 level (the 50-state level in the US for diesel light duty vehicles).
The opoc engine operates on the 2-cycle principle, generating one power stroke per crank revolution per cylinder. Each module consists of two opposing cylinders per module, with a crankshaft between them; each cylinder has two pistons moving in opposite directions. This design configuration eliminates the cylinder-head and valvetrain components of conventional engines, offering a more efficient, compact and simple core engine structure, the company says. The power density is more than 1 hp per pound of engine weight. The fully balanced opoc engine can be run on any liquid fuel.
|Cutaway diagram of the opoc engine. Click to enlarge.|
The EM100 comes in different power configurations, said Jonathan Hurden, Chief Engineer - Engine programs, and with different emissions outcomes. The Ecomotors website describes a military spec version of the EM100 (no emissions requirement) with 325 hp (242 kW) of power and 664 lb-ft (900 N·m) of torque. The basic commercial power version of the engine offers 300 hp (223 kW) of power and 550 lb-ft (746 N·m) of torque, with a fuel economy improvement of 15% compared to a conventional engine, Hurden said. (These figures are all for diesel.)
Opoc modules can be combined through the use of an electrically controlled clutch, with select modules deactivated at different points in the operating cycle to optimize fuel consumption (cylinder deactivation, but on a module basis). The clutch assembly is housed between two engine modules, and is engaged when both modules are running to deliver power from both modules through the drivetrain.
When the power of the second module is not needed, the clutch is disengaged, allowing the second engine to stop completely. This not only improves fuel economy, it also eliminates parasitic power losses in the primary module. A dual module opoc offers a 45% improvement in fuel efficiency, according to EcoMotors. A dual module Class 8 truck would use two 240 hp (179 kW) modules (“because we don’t need more than 480 hp total”, Hurden said) and meet Tier 2 Bin 5 emissions requirements on diesel.
With no valvetrain, the opoc engine has 40% less friction than conventional valve-controlled engines. The engine design features 90% cylinder scavenging, a high-pressure fuel injection system, and an electrically controlled turbocharger, allowing it to run higher levels of EGR. Four features allow the opoc engine to achieve that high 90% scavenging:
- Asymmetric port timing
- Circumferential ports
- Uni-flow air charging
- Electronically-controlled turbocharging
|The turbocharger unit with electric motor. Click to enlarge.|
The electrically controlled turbocharger (ECT) incorporates an electric motor into the turbo assembly. In essence, it provides a supercharger, driven by the electric motor, as an adjunct to the exhaust-driven turbocharger. Boost pressure can be created by the electric motor, the turbocharger, or both.
The ECT effectively eliminates turbo lag because the electric motor provides much faster turbine response, and also provides boost when there is low energy from the exhaust flow. The motor is actuated by an electronic controller, which can be integrated with the engine control unit. When it is being spun by the turbocharger, the electric motor acts as generator, producing electricity.
While some two-stroke engines suffer from high oil consumption, the opoc engine’s oil consumption is 0.2 grams per kilowatt-hour, as compared to 0.4 grams per kilowatt-hour of a standard four-stroke engine, according to Ecomotors. Because the opoc is a direct gas exchange engine, the only components exposed to combustion gases are the piston top, rings and cylinder wall—less than in a conventional four-stroke engine, where lubricated components such as valve stems are exposed.
Ecomotors is also developing a smaller version of the opoc, the EM65 (65mm bore diameter), with 75 hp per module, and targeted for light duty vehicle gasoline and flex-fuel applications.