One of the technologies Eurocopter is pursuing under its Bluecopter initiative to reduce the environmental footprint of rotorcraft is a diesel-powered light helicopter. Diesels promise a dramatic reduction in fuel consumption over gas turbines, but require a significant increase in power-to-weight ratio to be competitive in aircraft.
At this week's Heli-Expo show in Houston, Eurocopter is showcasing one of the diesel-engine options it is looking at - US firm EcoMotors' Opposed Piston Opposed Cylinder (OPOC) design.
Credit: Jeff Lenorovitz
The patented OPOC is a two-stroke engine with two horizontally opposed cyliners, each with two pistons moving in opposite directions - all connected to a central crankshaft. EcoMotors CEO Don Runkle says the OPOC is half the size and half the weight, with half the fuel consumption and less than half the parts of a conventional diesel engine - which explains Eurocopter's interest.
In this video, EcoMotors' chief technology officer Prof. Peter Hofbauer explains how the OPOC engine works:
CEO Runkle says EcoMotors started developing the OPOC for DARPA, to power the A160T Hummingbird unmanned helicopter, but that part of the program was cancelled and the company is now focusing initially on the power-generator and commercial-vehicle markets. It's first engine is the EM100, with a design power density of 1.1hp/lb. By comparison, Thielert's Centurion turbo-diesel aero-engines have power-to-weight ratios of around 0.5hp/lb.
One advantage of the OPOC design for helicopters and unmanned aircraft, Runkle says, is its modularity. The two-cylinder modules can be linked together via an electronic clutch, so the OPOC can operate as a dual-module engine for take-off and hover, when high power is needed, then one module can be disconnected and shut down in the cruise, saving fuel, when only partial power is needed.
Runkle believes the dual-module EM100 engine now under development should be able to meet Eurocopter's requirements for demonstration in an EC120 light helicopter, but says a version specifically designed for aircraft could be made even lighter, perhaps by using magnesium instead of aluminium for the block.
EcoMotors plans to have an engine ready for the generator market by the end of 2011, with a version of the commercial-vehicle market following 12-18 months later because of the stringent emissions testing required.