Combustion engines are often used for power generation applications. These engines can be gaseous-fuel driven and implement lean burn, during which air/fuel ratios are higher than in conventional engines. For example, these gas engines can admit about 75% more air than is theoretically needed for stoichiometric combustion. Lean-burn engines increase fuel efficiency because they utilize homogeneous mixing to burn less fuel than a conventional engine and produce the same power output.
Though using lean burn may increase efficiency, gaseous fuel-powered engines may be limited by variations in combustion pressures between cylinders of the engine. Gaseous fuel-powered engines are typically pre-mix charge engines, where fuel and air are mixed within an intake manifold and then admitted to a combustion chamber of the engine. Variations in combustion pressure result from more air/fuel mixture being admitted into some cylinders than into other cylinders. This uneven distribution of the air/fuel mixture can result in pockets of the air/fuel mixture burning outside of the envelope of normal combustion, increasing the tendency for an engine to knock. The combustion pressure variations can result in cylinder pressures that are significantly higher than average peak cylinder pressures normally seen within the engine. And, because significantly higher cylinder pressures can cause the engine to operate improperly, a margin of error is required to accommodate the pressure variations. As a result, the engine may be required to operate at a level far enough below its load limit to compensate for the pressure variation between the cylinders, thereby lowering the load rating of the engine. Additionally, the pressure variations can cause fluctuation in engine torque and speed, which may be undesirable for some electrical power generation applications.
An exemplary natural gas engine system is described in U.S. Pat. No. 7,210,457 B2 (the '457 patent), issued to Kuzuyama on May 1, 2007. The '457 patent discloses an engine having a plurality of cylinders that are associated with a variable valve timing device. The '457 patent also discloses a control apparatus and a sensor that detects information related to the combustion state within the cylinders. Based on information provided by the sensor, the control apparatus identifies the one cylinder having the most violent combustion. The control apparatus then controls the variable valve timing device to adjust a valve timing of all of the cylinders based on the identification. The control apparatus also adjusts a fuel injection amount to all of the cylinders based on the identification. The control apparatus thereby suppresses the combustion of all of the cylinders such that the combustion state of the most violent cylinder becomes an appropriate combustion state.
Although the engine system of the '457 patent may limit excessive pressures in any one cylinder by suppressing combustion in all of the cylinders, the benefit thereof may be limited. That is, because the controller of the '457 patent simultaneously reduces the combustion of all of the cylinders by the same amount, the controller of the '457 patent may fail to properly balance the loading between the cylinders. A load imbalance may result in fluctuations in engine torque and speed that can negatively affect electrical power generation. Further, the controller of the '457 patent may needlessly reduce output of all cylinders, where reduction of only one cylinder is required, thereby lowering an overall rating of the engine.
The present disclosure is directed to overcoming one or more of the shortcomings set forth above and/or other deficiencies in existing technology.