Semi-closed cycle fault tolerant control system and method in an exhaust system

An exhaust system with a semi-closed cycle, comprising:

• a main flow path configured to carry one or more gases, wherein the main flow path has an inlet node, an outlet node, and a recirculation node arranged between the inlet node and the outlet node;
• an exhaust gas recirculation (EGR) flow path coupled to the main flow path and configured to divert a recirculated exhaust gas from the main flow path, at the recirculation node, and recirculate the recirculated exhaust gas to the inlet node;
• an engine arranged on the main flow path downstream from the inlet node, wherein the engine is configured to receive a gas mixture including ambient air and the recirculated exhaust gas, and produce an exhaust gas;
• a cooling system arranged on the main flow path downstream from the engine, wherein the cooling system is configured to cool the exhaust gas;
• a draft fan arranged on the main flow path downstream from the cooling system, wherein the draft fan is configured to receive at least a first portion of the exhaust gas from the cooling system and control a gas flowrate through the main flow path;
• an EGR fan arranged on the EGR flow path and configured to regulate a flowrate of the recirculated exhaust gas to the main flow path based on a gas concentration of a target gas in the main flow path;
• a gas concentration sensor provided in the main flow path upstream from the cooling system,
• wherein the gas concentration sensor is configured to generate a first sensor signal representative of the gas concentration of the target gas, and wherein the target gas is an oxygen gas or a CO2 gas;
• and
• a first fan controller configured to regulate a fan speed of the EGR fan based on the first sensor signal in order to regulate the flowrate of the recirculated exhaust gas diverted from the main flow path such that the gas concentration is maintained within a target gas concentration range.

A semi-closed cycle control method in an exhaust system, the method comprising:

• providing one or more gases to a main flow path including an inlet node, an outlet node, and a recirculation node arranged between the inlet node and the outlet node;
• diverting, at the recirculation node, a recirculated exhaust gas from the main flow path back to the inlet node via an exhaust gas recirculation (EGR) flow path coupled to the recirculation node and the inlet node;
• producing an exhaust gas, via combustion, using a gas mixture comprising ambient air and the recirculated exhaust gas;
• cooling the exhaust gas to produce a cooled exhaust gas, wherein the recirculated exhaust gas includes a portion of the cooled exhaust gas;
• and
• controlling a fan speed of a draft fan arranged on the main flow path to regulate a gas flowrate through the main flow path and a pressure in a stack flow path,
• wherein the stack flow path is an offshoot of the main flow path,
• wherein controlling the fan speed of the draft fan comprises regulating the fan speed of the draft fan based on a pressure in the stack flow path in order to maintain the pressure in the stack flow path at a target gauge pressure, and
• wherein the target gauge pressure is zero or less than zero.