(e-book version)Need: The pipeline industry uses over 8,000 large bore engines in gas transmission/compression service’. These engines are typically gas fueled and spark ignited. Some early versions of the engines are piston scavenged, but most are turbocharged. Some models, especially those equipped for lean burn operation, utilize pre-combustion chambers for enhanced ignition. Typically, the gaseous fuel is admitted directly into the top of the engine combustion chamber by a cam-operated, mechanical gas admission valve (MGAV). The MGAV is operated by an engine driven cam, cam follower, push rod, and rocker assembly. Such mechanisms offer little in the way of adjustability of the gas admission event: the ability to change the start of gas admission (SOA) and end of gas admission (EOA). The gas admission system is generally optimized for a particular mode of engine operation, typically rated speed and full load, and is fixed in that state. Desired changes in the gas admission cycle are not easily accomplished. At the same time, however, undesired changes commonly occur due to wear, failure, and mis-adjustment of the MGAV drive train.
Benefit: This report documents the development of a natural gas-fueled large-bore engine test bed (LBET) at Colorado State University and the subsequent test of an electronic gas admissions valve (EGAV) with in-cylinder pressure feedback. The LBET is now a state-of-the-art natural gas-fueled test facility. It will be open for use in late 1994 or early 1995 to all parties interested in testing equipment that might lead to safer, more economical and cleaner burning gas fueled engines. The EGAV tests were successful. The valve allows for precise control of fuel admission and end of admission timing. This results in the engine running in a real-time balance condition. Laboratory tests showed a 30% reduction of hydrocarbons and nitrous oxides reductions with a 2% reduction in fuel consumption. Field testing will continue in 1995 prior to commercialization.
Result: The performance of the electronically autobalanced engine was compared to that of the manually balanced engine with a 100 psi imbalance. This is just outside of the manufacturer’s definition of “balance” (75 psi), and considerably better than the level of balance commonly found in field engines. The use of autobalancing reduced the incidence of engine misfires at 75% load from 35% in the manually balanced case to 10% in the autobalanced case. At 100% load, the engine with a 25% imbalance (one of the four cylinders adjusted to a peak pressure 100 psi lower than the others) showed a 5% misfire rate while the autobalanced engine had essentially no misfires. At 75% load, the use of autobalancing reduced hydrocarbon emissions by 33%, from 22 grams/BHP•hr to 14 grams/BHP•hr. The autobalancing feature reduced fuel consumption by as much as 2%, depending on load. NOx reductions of 2.6 grams/BHP•hr at full load were demonstrated, which represents a 30% reduction. NOx reductions of greater than 2.0 grams/BHP•hr were seen at all loads.
