TECHNICAL FIELD

The present disclosure relates generally to dual fuel engines and more particularly to systems and methods for controlling air flow of the engines to achieve a target exhaust temperature and thereby improve engine performance.

BACKGROUND OF THE DISCLOSURE

Dual fuel engines burn diesel fuel and natural gas simultaneously in an air-fuel mixture. The gas and air are typically mixed upstream of the engine cylinders and then are drawn into the engine cylinders. For each cylinder, near the end of the compression stroke, diesel fuel is injected. When the diesel fuel compression ignites, it causes the natural gas to also burn. The combined combustion releases energy that powers the engine. The air-fuel ratio of the mixture has a direct impact on the performance of the engine. If the air-fuel ratio is too rich, then the thermal limits of the engine may be exceeded, or the combustion may be too fast, causing excessive cylinder pressures or engine knock, which may cause engine damage. If the air-fuel ratio is too lean, then combustion of the natural gas-air mixture may be incomplete, reducing the overall efficiency of the engine and increasing the undesirable emissions such as unburned hydrocarbons.

The optimal air-fuel ratio depends upon several highly variable parameters including the current engine speed, current load, the quality of the natural gas, the temperature and humidity of the intake air and the ambient pressure (i.e., altitude). Methods exist for directly controlling the air-fuel ratio by measuring at least some of these variable parameters and adjusting the air-fuel ratio to account for the variations yet still provide the desired engine performance. In general, such approaches are complex and expensive to implement. Accordingly, an alternative approach to controlling the performance of a dual fuel engine is desirable.

SUMMARY OF THE DISCLOSURE

In one embodiment, the present disclosure provides systems for controlling operation of a dual fuel engine, comprising a sensor configured to measure an exhaust temperature, a processor in electrical communication with the sensor, and a non-transitory memory having instructions that, in response to execution by the processor, cause the processor to determine a target exhaust temperature, receive a measured exhaust temperature from the sensor, determine an exhaust temperature deviation by comparing the measured exhaust temperature to the target exhaust temperature, compare the exhaust temperature deviation to a threshold, adjust at least one of a diesel injection start of injection, a rail pressure, an intake throttle, a wastegate, a compressor bypass valve, an exhaust throttle, a variable geometry turbocharger and engine valve timing when the exhaust temperature deviation exceeds the threshold to control charge-flow to the engine, and repeatedly adjust until the exhaust temperature deviation is less than the threshold. In one aspect of this embodiment, determining a target exhaust temperature includes accessing a lookup table including predetermined associations between target exhaust temperatures and at least one of current engine power and current engine speed. In another aspect, the engine includes a first bank of cylinders and a second bank of cylinders, and adjusting includes separately controlling charge-flow to each of the banks of cylinders to balance operation of the banks of cylinders. As used herein, the balancing of the operation of the bank of cylinders is not particularly limited and may be understood to include at least balancing power output, temperatures, pressures (e.g., manifold pressure, cylinder pressure, etc.). In another variant, the engine includes a first bank of cylinders and a second bank of cylinders, and adjusting includes separately controlling charge flow to each of the banks of cylinders to balance one of exhaust temperatures of the banks and intake manifold pressures of the banks.

According to another embodiment, the disclosure provides a method of controlling a dual fuel engine with at least two banks of cylinders, comprising sensing temperatures of exhaust from the at least two banks, and adjusting a gas flow to one of the at least two banks to balance exhaust temperatures of the at least two banks. In a variant of this embodiment, the method further includes lowering the gas flow to one of the at least two banks while increasing the gas flow to the other of the at least two banks by a similar amount to maintain a substantially constant total gas flow to the engine. As used herein, the term “sensing” is not particularly limited and may include the use of physical sensors, virtual sensors (e.g., calculations from physical sensors elsewhere), or mixtures thereof.

In another embodiment, methods of controlling a dual fuel engine with at least two banks of cylinders, comprising sensing at least one of temperatures of exhaust from the at least two banks and a pressure of an intake manifold of each of the at least two banks, and adjusting at least one of a gas flow to one of the at least two banks to balance exhaust temperatures of the at least two banks, a charge flow to one of the at least two banks to balance exhaust temperatures of the at least two banks, and an air flow to one of the at least two banks to balance exhaust temperatures of the at least two banks and intake manifold pressures of the at least two banks are provided.

In yet another embodiment, the disclosure provides a method of controlling a dual fuel engine with at least two banks of cylinders, comprising sensing a pressure of an intake manifold of each of the at least two banks, adjusting a gas flow to one of the at least two banks, and adjusting an air flow to one of the at least two banks to balance exhaust temperatures of the at least two banks and intake manifold pressures of the at least two banks.

Also disclosed are various systems for controlling operation of a dual fuel engine, comprising a sensor configured to measure an exhaust temperature, a processor in electrical communication with the sensor, and a non-transitory memory having instructions that, in response to execution by the processor, cause the processor to determine a target exhaust temperature, receive a measured exhaust temperature from the sensor, determine an exhaust temperature deviation by comparing the measured exhaust temperature to the target exhaust temperature, compare the exhaust temperature deviation to a threshold, adjust at least one of a diesel injection start of injection, a rail pressure, an intake throttle, a wastegate, a compressor bypass valve, an exhaust throttle, a variable geometry turbocharger and engine valve timing when the exhaust temperature deviation exceeds the threshold to control charge-flow to the engine, and repeatedly adjust until the exhaust temperature deviation is less than the threshold.

In various embodiments, duel fuel engines may switch from two banks to single bank operation. In some embodiments, the switching may be accompanied by deactivating engine valves on the non-fueled bank. In various embodiments this may be accomplished by adjusting the intake throttle, wastegate, compressor bypass, or variable geometry turbocharger (“VGT”) to desired positions, for example, to limit air flow through the non-fueled bank.

