Apparatus and method for regulating gaseous fuel pressure and mitigating emissions in an internal combustion engine system

An internal combustion engine system fueled with a gaseous fuel comprising:

• a storage vessel storing the gaseous fuel in a gas state as a compressed gas at a storage pressure, the storage pressure decreasing as an internal combustion engine consumes the gaseous fuel;
• a pressurizer in fluid communication with the storage vessel for pressurizing the gaseous fuel above the storage pressure;
• a bypass valve in fluid communication with the storage vessel and operable between an open position allowing flow of gaseous fuel therethrough bypassing the pressurizer and a closed position blocking flow of the gaseous fuel therethrough;
• a gaseous-fuel rail in fluid communication with the pressurizer and the bypass valve to receive the gaseous fuel;
• a first pressure sensor generating signals representative of a storage pressure of the gaseous fuel in the storage vessel;
• a second pressure sensor generating signals representative of an injection pressure of the gaseous fuel in the gaseous-fuel rail;
• a controller operatively connected with the pressurizer, the bypass valve, and the first and second pressure sensors, the controller programmed to:
• receive the signals from the first and second pressure sensors and determine the storage pressure and the injection pressure respectively;
• selectively command the pressurizer to pressurize the gaseous fuel from the storage pressure to a second pressure in the fuel rail;
• and
• selectively command the bypass valve between the closed position and the open position;
• for an engine speed and an engine load condition the controller is further programmed to:
• determine a storage-pressure brake thermal efficiency based on the injection pressure where the gaseous fuel is delivered to the fuel rail without increasing gaseous fuel pressure from the storage pressure whereby the injection pressure of the gaseous fuel is equal to the storage pressure of the gaseous fuel within a first margin;
• determine a second-pressure brake thermal efficiency based on the injection pressure and an energy cost of pressurizing the gaseous fuel from the storage pressure to the second pressure whereby the injection pressure is equal to the second pressure within a second margin;
• command the pressurizer to pressurize the gaseous fuel from the storage pressure to the second pressure in the fuel rail when the second-pressure brake thermal efficiency is greater than the storage-pressure brake thermal efficiency;
• and
• command the bypass valve to the open position when the second-pressure brake thermal efficiency is less or equal to the storage-pressure brake thermal efficiency.