|A view of hydrogen combustion through an endoscope. The red and yellow areas show the more intense temperatures.|
Engineers at the US Department of Energy’s Argonne National Laboratory have captured the first images of hydrogen combustion in an internal combustion engine operating at real-world speeds and loads.
The hydrogen combustion imaging is part of a larger project to optimize the efficiency of hydrogen-burning internal combustion engines.
Several years ago, X-ray images of combustion inside a diesel engine made by researchers in Argonne’s Engines and Emissions Group revealed an unexpected shockwave as diesel fuel spurted out of the fuel injector. This earlier research is helping to improve fuel injectors and increase diesel efficiency.
Using imaging tools and other standard engine measurement devices on a Ford single-cylinder, direct-injection hydrogen engine, Argonne mechanical engineers Steve Ciatti, Henning Lohse-Busch and Thomas Wallner are optimizing engine operation and identifying the root causes of combustion anomalies, such as pre-ignition and knock. These problems are more pronounced at high speeds and high loads. Argonne researchers observe 50 performance measurements during each engine test.
Researchers use ultraviolet imaging to capture images of combusting hydrogen inside the running engine.
Hydrogen’s visible radiation signature is barely discernible, so we focused on the chemical reactions of hydrogen and oxygen, called OH chemiluminescence, in the engine.—Steve Ciatti, principal investigator
Hydrogen has wide flammability limits, so the engine does not need a throttle, a device that chokes the air/fuel mixture to control the engine power and hampers efficiency (a standard car today is 25% efficient; a hydrogen car could be close to 45% efficient), nor do they require exhaust after-treatment when operating correctly.
Hydrogen’s high flame speed also offers a chance to increase the power output without increasing engine size. Using a direct injection of hydrogen, the power density is roughly 117% that of an equivalent gasoline engine—and hydrogen ICEs start easily in cold weather. However, unlike liquid fuels, hydrogen has low energy density per unit volume, resulting in somewhat limited range by comparison. The significant increase in efficiency will help to mitigate this characteristic.
Hydrogen easily combusts, so researchers are experimenting with a multiple injection approach. They are injecting hydrogen directly into the cylinder once or twice during each combustion cycle, depending upon operating conditions. The goal is to determine the optimum timing and amount of hydrogen injected each cycle. The wrong mixture of hydrogen causes engine operation and emission problems.
The researchers are also experimenting with prototype injectors. Making them is a materials science and engineering challenge because the operating atmosphere is unusually hot and under high pressure. Sealing and cooling the injector becomes a critical task. Researchers are also determining the most efficient and cleanest way to run the engine without knock or pre-ignition, another technical challenge.
The team will next move its work to a 2.3-liter four-cylinder Ford hydrogen engine, and then integrate that engine into a flexible hybrid vehicle for further testing.
This research is funded by the DOE Office of Energy Efficiency and Renewable Energy’s FreedomCAR and Vehicle Technologies Program. Argonne researchers are collaborating with Sandia National Laboratories, Ford, BMW and the European Hydrogen Internal Combustion Engine (HyICE) initiative.
Hydrogen burn video