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The arc characteristics and discharge behavior of a representative inductive spark ignition system were characterized with a spark plug calorimeter and a constant volume vessel used to create high-pressure crossflow velocities through the gap of the spark plug. A 14 mm diameter natural gas engine spark plug was used for the measurements. The discharges were into a non-combusting gas, primarily nitrogen. The spark plug calorimeter was used to determine the electrical-to-thermal energy conversion in the spark gap under quiescent conditions, while the constant volume vessel was used to study ignition arc structure in convective crossflows and imaged with a high-speed camera. Topics included the effect of crossflow velocity, pressure (up to 20 bar at 300 K), and gap distance on breakdown voltage, arc duration and delivered electrical energy. Also of interest was the amount of remaining electrical energy on the coil versus spark duration in a cross flow.

Ignition of extremely lean or dilute mixtures is a very challenging problem. Therefore, it is essential for the engine development engineer to understand the fundamentals and limitations of existing ignition systems. This paper presents a new railplug ignition concept, a high-energy ignition system, which can enhance ignition of very lean mixtures by means of its high-energy deposition and high velocity jet of the plasma. This paper presents initial results of tests using an inductive ignition system, a capacitor discharge ignition system, and a railplug high-energy ignition system. Discharge characteristics, such as time-resolved voltage, current, and luminous emission were measured. Spark plug and railplug ignition are compared for their effects on combustion stability of a natural gas engine. The results show that railplugs have a very strong arc-phase that can ensure the ignition of very dilute mixtures.

As natural gas engines are designed to operate leaner and with increased boost pressure, durability of the spark plugs becomes problematic. Among the various new ignition devices that have been considered to solve some of the problems facing spark plugs, railplugs appear to hold clear advantages in some areas. There are two types of railplugs: coaxial rail and parallel rail. This paper reports the results of an experimental study of various parameters that affect the performance of parallel railplugs. Their performance was quantified by the distance that the arc traveled along the rails from the initiation point. Travel along the rails is thought to be an important performance metric because rail-travel limits excessive local wear and produces a distributed ignition source which can potentially reduce mixture inhomogeneity induced ignition problems.

It is a very challenging problem to reliably ignite extremely lean mixtures, especially for the low speed, high load conditions of large-bore natural gas engines. If these engines are to be use for the distributed power generation market, it will require operation with higher boost pressures and even leaner mixtures. Both place greater demands on the ignition system. The railplug is a very promising ignition system for lean burn natural gas engines with its high-energy deposition and high velocity plasma arc. It requires care to properly design railplugs for this new application, however. For these engines, in-cylinder pressure and mixture temperature are very high at the time of ignition due to the high boost pressure. Hot spots may exist on the electrodes of the ignitor, causing pre-ignition problems. A heat transfer model is proposed in this paper to aid the railplug design. The electrode temperature was measured in an operating natural gas engine.

Spark discharge properties were studied and characterized for varying gas compositions and spark plug geometries using a spark calorimeter and constant volume optical vessel. Two different 18 mm natural gas engine spark plugs were used in the experiments. All measurements were recorded under quiescent conditions and with a spark gap of 0.30 mm. The spark plug calorimeter was used for measuring thermal energy deposition to the gas for gas compositions of nitrogen, a stoichiometric mixture of nitrogen and methane, a stoichiometric mixture of nitrogen and methane diluted with 30% carbon dioxide by volume, and for air. Other measurements of interest included breakdown voltage, electrical energy delivered to the spark gap, electrical-to-thermal energy conversion efficiency, and spark duration, for pressures up to 28 bar at 300 K. The optical vessel was used for the combusting mixture of stoichiometric air and methane at pressures up to 28 bar.

An experimental study of the spark ignition process for SI engines was conducted to study spark plug erosion and the effect of breakdown voltage/energy on electrode surface deformation. The experiments were conducted outside of an engine, in both a pressurized constant volume optical chamber and in a high-pressure vessel heated within a furnace with gas temperatures as high as 730°C. J-gap spark plugs designed for natural gas engines were studied at elevated temperature and under a range of pressures to investigate electrode wear characteristics. Both iridium-alloy and platinum-alloy cathode (center electrode) and anode (ground strap) spark plugs were investigated. In addition, single spark events were performed on polished platinum cathode surfaces to allow the visualization of craters from individual spark events in order to quantify how their size and shape were affected by energy deposition and breakdown characteristics.