Extending Lean Operating Limit and Reducing Emissions of Methane Spark-Ignited Engines Using a Microwave-Assisted Spark Plug

Figure 6

The percent change in NO_𝑥 emissions with 1600 mJ microwave-enhanced ignition from NO_𝑥 emissions with spark-only ignition. Under stable operating conditions (𝜆=1.46), addition of microwave energy increases NO_𝑥 production by 13% (~100 ppm). Increasing 𝜆 further increases NO_𝑥.