FALL/WINTER 2005-06 — Engine and Emissions

Optimizing Direct-Injection Hydrogen Engine Operation

Direct-injection (DI) hydrogen (H2) engines hold promise for transportation because of their high thermal efficiency (approaching 50%), high power density, reduced emissions, low cost, and lack of cold-start problems. Overall, they can help develop the U.S. hydrogen infrastructure to ensure that H2 vehicles become an every day reality on the road.

However, H2 engines pose unique combustion challenges. Combustion anomalies such as pre-ignition and knock create operational challenges. These challenges are especially prevalent when the engine is operating under high-speed/high-load conditions. However, hydrogen possesses several characteristics that offer significant advantages. The wide flammability limits of hydrogen provide the opportunity to run the engine without a throttle, increasing efficiency. The high flame speed of hydrogen offers the chance to increase the power output of the engine without increasing its size.

Fuel Economy Effects of Different Operating Regimes on Efficiency of Hydrogen Vehicle Engines

OH* intensity as a function of crank angle. The red line is the OH* intensity. The blue line is a pressure-derived heat release trace that shows how rapidly combustion energy is converted into mechanical energy. Note how the rising slopes and the peaks of each line are very similar - meaning that the OH* signal mirrors the heat release quite well. The downward slope of the OH* signal is more shallow because OH* is present in the exhaust products for a brief time, even though the combustion energy to the piston has been consumed.

This full-combustion image of OH* shows the number of H + O = OH* reactions that occur inside a direct-injection hydrogen engine. It provides a qualitative assessment of where (areas in white, red, and green) and how rapidly those combustion reactions occur. The image was taken at 2,000 RPM and with 6 bar indicated mean effective pressure (IMEP), which is about 75% load. The engine was fueled by gaseous hydrogen using a port fuel injector.

Building on work performed by researchers at the Technical University of Graz, Austria, these challenges are being addressed in depth at Argonne. CTR researchers are collaborating with Sandia National Laboratories, Ford, BMW, and HyICE to acquire more detailed information over the high end of the engine's operating range. By using imaging tools and other standard engine measurement devices on a Ford single-cylinder DI H2 engine, they are optimizing operation and identifying the root causes of combustion anomalies. With ultraviolet imaging, the team is capturing OH* chemiluminescence inside the engine while running at high speeds and loads. (OH* emits photons in the ultraviolet spectra, caused by the chemical reaction of H2 and O2 in the air, and that light can be captured with specialized optics.)¹ Furthermore, researchers are taking a multiple-injection approach to reduce or eliminate combustion problems while simultaneously reducing nitrogen oxides (NOx) emissions in the engine.

A prototype direct-injection injector, constructed by Westport Innovations of Vancouver, BC, Canada, is being operated to further expand the operating regimes of H2 engines.

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¹ The asterisk signifies the excited state of the OH radical, and it is this excited state that produces the photon as the radical changes to its ground state.

Sponsor

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, FreedomCAR and Vehicle Technologies Program

Contact

Steve Ciatti

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