In their quest to develop more efficient engines, engineers have lost their spark. Modern gasoline-powered engines are smaller, but generate more power and fewer emissions than ever before. To accomplish this feat, engineers use turbochargers to boost the pressure inside an engine until spark-based ignition systems sputter.
“Under high temperatures and pressures, spark plugs are difficult to ignite and don’t last long,” said Douglas Longman, section manager in Engine Combustion Research at Argonne.
The problem affects engines of all types - from car and truck engines to large stationary engines running on natural gas to generate electricity.
To solve the problem, researchers at Argonne National Laboratory are evaluating and developing advanced ignition systems that, unlike traditional spark ignition systems, tolerate and even thrive in the challenging operating conditions of modern engines.
Researchers of advanced ignition systems have discovered innovative ways to improve upon the conventional spark plug, including systems that use lasers, transient plasma, and “corona” ignition (think lasers on the top of a rook in chess).
Argonne’s multi-disciplinary teams of engineers, computer scientists and physicists are making ground-breaking discoveries in this field. Argonne’s discoveries stem from its unique strengths in both fundamental science and applied research and development. Longman and his colleagues across the laboratory not only discover which new technologies outperform spark plugs under challenging engine conditions, but why they do so.
Argonne’s insights arise as scientists from different fields approach ignition from all angles. “We cover the whole ignition realm,” said Thomas Wallner, section manager in Vehicle Systems and Interoperability at Argonne. Wallner, Longman and their peers experiment on many engine platforms, apply this new data to models that simulate ignition, and also investigate how ignition unfolds in real time with ultra-bright, high-energy x-rays generated by Argonne’s Advanced Photon Source.
Lightening takes ignition by storm
One reason that advanced ignition systems tend to outperform spark ignition is because lasers, transient plasmas or the crown-like corona arrangement can trigger the ignition process potentially anywhere in the engine’s combustion chamber. “It’s like a lightning strike,” said Wallner. These setups also extend the systems’ lifespans. (By contrast, spark plugs must overcome the gap between electrodes and always ignite on the side of the combustion chamber – a less efficient approach.)
Longman’s and Wallner’s work revolves around Argonne’s Engine Research Facility and Distributed Energy Research Center in which they test advanced ignition systems on various engines, ranging from small single- and multi-cylinder platforms to large stationary engines.
After testing laser ignition on a single-cylinder engine, Argonne engineers Sreenath Gupta and Bipin Bihari patented a new technique to deliver laser pulses to an entire six-cylinder engine for the first time. Gupta’s and Bihari’s laser-ignition approach improved engine efficiency by up to 3% or reduced nitrogen-oxide emissions by up to 70%.
The experiment-modeling loop
Yet these successful experiments are only the first step toward optimizing advanced ignition systems. Argonne engineers then feed experimental data into supercomputers at the Argonne Leadership Computing Facility (ALCF) to improve and develop computational models of existing and advanced ignition systems.
“Our experimental and modeling teams work together in a loop,” said Riccardo Scarcelli, an engine research engineer at Argonne. “The data helps us to build and validate our models, and then we try to use those models to design optimized devices. Simulations give you a hint of how ignition systems could perform better,” said Scarcelli.
Ignition is so complex that most computational models of spark-based ignition systems remain fairly simplistic. Yet with its world-class facilities and expertise, Argonne is leading the way, refining these models as well as pioneering new models of advanced systems.
To develop new models, Scarcelli and his colleagues first study the basic physics of the ignition process. While spark ignition systems generate hot plasma, corona systems act differently, so modelers need to change their assumptions. “For example, instead of introducing heat in your model, you could use a high amount of ions or electrons – that would still trigger combustion,” said Scarcelli.
Digging deeper at the Advanced Photon Source
How do advanced ignition systems actually behave? Argonne researchers are now shedding light on ignition with endoscopes, which peer directly into combustion chambers, and the Advanced Photon Source, which produces bright, x-rays. Argonne physicists at the APS have already mapped spark-based ignition systems. Now Argonne and its partners at Sandia National Laboratories have started evaluating transient plasma ignition and are preparing to measure Gupta’s and Bihari’s laser igniters as well.
Along with experimental engine data, advanced diagnostics from the APS and Sandia provide detailed measurements that help refine Scarcelli’s models and help his colleagues to further optimize engine performance and reduce emissions.
Moving beyond the spark
By advancing the field of ignition systems through experiments, modeling, and optical research, Argonne is helping the U.S. attain energy independence and support innovation across the energy sector.
This research is funded by the Department of Energy’s Office of Energy Efficiency and Renewable Energy.