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

Abstract

A microwave-assisted spark plug was used to extend the lean operating limit (lean limit) and reduce emissions of an engine burning methane-air. In-cylinder pressure data were collected at normalized air-fuel ratios of λ = 1.46, λ = 1.51, λ = 1.57, λ = 1.68, and λ = 1.75. For each λ, microwave energy (power supplied to the magnetron per engine cycle) was varied from 0 mJ (spark discharge alone) to 1600 mJ. At lean conditions, the results showed adding microwave energy to a standard spark plug discharge increased the number of complete combustion cycles, improving engine stability as compared to spark-only operation. Addition of microwave energy also increased the indicated thermal efficiency by 4% at λ = 1.68. At λ = 1.75, the spark discharge alone was unable to consistently ignite the air-fuel mixture, resulting in frequent misfires. Although microwave energy produced more consistent ignition than spark discharge alone at λ = 1.75, 59% of the cycles only partially burned. Overall, the microwave-assisted spark plug increased engine performance under lean operating conditions (λ = 1.68) but did not affect operation at conditions closer to stoichiometric.

Stability Limit Extension of a Wet Ethanol-fueled SI Engine using a Microwave-assisted Spark

“…Generation or enhancement of plasma in a combustion environment through the use of microwaves (MW), radio frequency waves (RF), dielectric barrier discharges (DBD), nanosecond discharges, and other electric discharges has been shown to improve ignition characteristics and flame speeds under a variety of conditions and is thus an active area of research, as evidenced by the review by Starikovskaia [11] and later by Starikovskiy et al [12]. Applications include high-speed scramjet combustion for aerospace applications [13,14] and automotive internal combustion engines [15][16][17][18][19][20][21].…”

Effect of Ignition Energy and Hydrogen Addition on Laminar Flame Speed, Ignition Delay Time, and Flame Rising Time of Lean Methane/Air Mixtures

“…The use of alternative fuels, together with lean combustion technology, is an effective way of reducing emissions and enhancing the thermal efficiency of internal combustion engines (ICE) [1][2][3][4][5][6]. Natural gas (mostly methane) and hydrogen are considered the alternative fuels for ICEs.…”

Experimental Research on Microwave Ignition and Combustion Characteristics of ADN-Based Liquid Propellant

“…It is theoretically possible to utilize this feature to ignite or support the combustion of all fuels. Microwave ignition devices have already been explored in vehicles and have made great strides [14][15][16][17]. After experiments, microwave plasma-assisted ignition has been shown to accelerate the combustion process based on the principle of generating non-equilibrium of chemically active particles.…”