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The Los Angeles County Metropolitan Transportation Authority (LACMTA) has a large fleet of CNG buses and several CNG refueling sites. Filtration canisters are installed in the fueling systems to remove incidental particulate matter in the gas stream. On three occasions, refueling system filter canisters ruptured and caused damage to nearby buses. This paper describes the failure investigation that was performed after one of these incidents. The elements of the investigation included determination of the root cause of failure, metallurgical examination of both incident and exemplar canisters, and non-destructive testing of similar components still in service. It also describes a hazard analysis, which was performed to help identify and rank other process hazards associated with CNG refueling operations. Since the completion of this investigation, all similar filters in the MTA system were replaced with improved canisters, constructed from higher strength materials.

With the implementation of a closed loop fuel control system, operation of lean-burn natural gas engines can be optimized in terms of reducing emissions while maximizing efficiency. Such a system would compensate for variations in fuel composition, but also would correct for variations in volumetric efficiency due to immediate engine history and long-term engine component wear. Present day engine controllers perform well when they are operated with the same gas composition for which they were calibrated, but because fuel composition varies geographically as well as seasonally, some method of compensation is required. A closed loop control system on a medium-duty lean-burn engine will enhance performance by maintaining the desired air-fuel ratio to eliminate any unwanted rich or lean excursions (relative to the desired air-fuel ratio) that produce excess engine-out emissions. Such a system can also guard against internal engine damage due to overheating and/or engine knock.

A set of experiments were conducted to evaluate the performance differences between a Low Heat Rejection Engine (LHRE) which is ceramic-insulated and a conventional baseline metal diesel engine which is water-cooled. Both engines were single cylinder, direct injection, and turbocharged. The objective of the study was to investigate the rate of heat release of these engines so that performance improvement procedures could be obtained. In this paper, the difference of the ignition delay between the two engines was determined. Two methods for improving the combustion process of the LHRE were studied: use of mixture fuels and increase the fuel injection rate. Both methods proved effective and reduced the fuel consumption rate of the LHRE.