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There are numerous off-road diesel engine applications. In some applications there is more focus on metrics such as initial cost, packaging and transient response and less emphasis on fuel economy. In this paper a combustion concept is presented that may be well suited to these applications. The novel combustion concept operates in two distinct operation modes: lean operation at light engine loads and stoichiometric operation at intermediate and high engine loads. One advantage to the two mode approach is the ability to simplify the aftertreatment and reduce cost. The simplified aftertreatment system utilizes a non-catalyzed diesel particulate filter (DPF) and a relatively small lean NOx trap (LNT). Under stoichiometric operation the LNT has the ability to act as a three way catalyst (TWC) for excellent control of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx).

Tests were conducted on a variety of commercially available spark plugs to determine the influence of igniter design on initial kernel formation and overall performance. Flame kernel formation was investigated using high-speed schlieren visualization. The flame growth rate was quantified using the area of the burned gas region. The results showed that kernel growth rate was heavily influenced by electrode geometry and configuration. The igniters were also tested in a bomb calorimeter to determine the levels of supplied and delivered energy. The typical ratio of supplied to delivered energy was 20% and igniters with a higher internal resistance delivered more energy and had faster kernel formation rates. The exception was plugs with large amounts of conductive mass near the electrodes, which had very slow kernel formation rates despite relatively high delivered energy levels.