The development of the DDC methanol engine has been an evolutionary process, with each subsequent configuration showing significant durability and/or emission improvement over its predecessor. Sixty demonstration engines are now in service in the field, including fifty-four (54) urban bus engines, five (5) truck engines, and one (1) generator set engine.
While nitrogen oxide (NOx) and particulate emissions from the methanol engine are inherently low, a durable solution to the effective control of hydrocarbon (HC) emissions has been an especially challenging area. The 1991 Federal urban bus transient emission standards (including 0.10 gm/bhp-hr particulate) have been met with several combinations of compression ratio, intake port height, exhaust valve cam profile, injector tip design, and electronic control strategies, and without exhaust aftertreatment devices or fuel ignition improvers. Significant development effort has also been focused toward catalytic converters in order to provide HC, CO, particulate, and formaldehyde emission levels substantially below the standards anticipated in the near future.
While lowering emissions, specific component development concerns were identified by incidents encountered during the field demonstrations, and dynamometer testing. The principal development areas involved fuel injectors, glow plugs, the glow plug controller, and cylinder heads (due to modifications required to accommodate glow plugs). Additional concerns included blower bypass control hardware, exhaust valve face and seat wear, and fuel pump gear wear. Special lubricating oils were found to reduce injector plunger seizure, reduce tip plugging, and preserve cylinder kit life. Top compression ring wear rates, with various candidate lube oils were determined using the Surface Layer Activation (SLA) technique. A detergent-type fuel additive was found to keep injector tips clean. Extensive use of statistically designed experiments and Finite Element Analysis led to improvements in each problem area.
Thus, solutions have been developed for all problems encountered during in-house testing and 1.8 million miles of field demonstration. Today, development efforts at DDC are focused toward the production release of the 6V-92TA methanol urban bus engine in 1991.