Dual fuel injection system

Abstract

A method of controlling fuel injection in a dual fuel engine system includes determining, with a first controller, a diesel injection pulse indicative of a first amount of diesel fuel to be injected into a combustion chamber of the engine and a first timing at which the first amount of diesel fuel is to be injected. The method also includes determining, with a second controller, a combined injection pulse based on the diesel injection pulse. The method further includes injecting the second amount of diesel fuel and the third amount of natural gas into the combustion chamber in accordance with the combined injection pulse. In such a method, injection in accordance with the combined injection pulse results in a combustion event characterized by a second combustion characteristic substantially equal to a first combustion characteristic associated with the diesel injection pulse.

What is claimed is: 
     
         1 . A method of controlling fuel injection in a dual fuel engine system, comprising:
 determining, with a first controller, a diesel injection pulse indicative of a first amount of diesel fuel to be injected into a combustion chamber of the engine and a first timing at which the first amount of diesel fuel is to be injected, wherein the diesel injection pulse is based on a set of operating parameters associated with the engine and wherein fuel injection in accordance with the diesel injection pulse would result in a first combustion characteristic within the combustion chamber sufficient to satisfy an output demanded of the engine using solely diesel fuel;   determining, with a second controller, a combined injection pulse based on the diesel injection pulse, wherein the combined injection pulse is indicative of a second amount of diesel fuel to be injected different than the first amount, a second timing at which the second amount of diesel fuel is to be injected different than the first timing, a third amount of natural gas to be injected, and a third timing at which the third amount of natural gas is to be injected; and   injecting the second amount of diesel fuel and the third amount of natural gas into the combustion chamber in accordance with the combined injection pulse, wherein the injection in accordance with the combined injection pulse results in a combustion event characterized by a second combustion characteristic substantially equal to the first combustion characteristic.   
     
     
         2 . The method of  claim 1 , wherein the set of operating parameters comprises at least one of vehicle speed, engine load, engine speed, intake temperature, and exhaust temperature. 
     
     
         3 . The method of  claim 1 , wherein the output demanded of the engine comprises at least one of engine speed, engine torque, engine acceleration, and engine deceleration. 
     
     
         4 . The method of  claim 1 , further comprising receiving, with the first controller, a first signal indicative of the output demanded of the engine, and determining the diesel injection pulse in response to receiving the first signal. 
     
     
         5 . The method of  claim 1 , wherein the first combustion characteristic comprises a torque generated by the engine. 
     
     
         6 . The method of  claim 5 , wherein the second timing is earlier in a piston cycle of the combustion chamber than the first timing. 
     
     
         7 . The method of  claim 5 , wherein the third timing is different than the second timing, and wherein the torque is generated during the combustion event by injecting the third amount of natural gas into the combustion chamber at the third timing. 
     
     
         8 . A method of controlling fuel injection in a dual fuel engine system, comprising:
 receiving a first signal indicative of at least one operating parameter associated with a dual fuel engine of the system;   determining, with a control system, a diesel injection pulse indicative of a first amount of diesel fuel to be injected into a combustion chamber of the engine and a first timing at which the first amount of diesel fuel is to be injected, wherein the diesel injection pulse is determined based on the at least one operating parameter and wherein fuel injection in accordance with the diesel injection pulse would result in a first combustion characteristic within the combustion chamber sufficient to satisfy an output demanded of the engine using solely diesel fuel;   generating, with the control system, a second signal indicative of the diesel injection pulse;   determining, with the control system, a combined injection pulse based on the second signal, wherein the combined injection pulse is indicative of a second amount of diesel fuel to be injected different than the first amount, a second timing at which the second amount of diesel fuel is to be injected different than the first timing, a third amount of natural gas to be injected, and a third timing at which the third amount of natural gas is to be injected;   directing a third signal indicative of the combined injection pulse to an injection system associated with the engine; and   injecting, with the injection system, the second amount of diesel fuel and the third amount of natural gas into the combustion chamber in accordance with the combined injection pulse, wherein the injection in accordance with the combined injection pulse results in a combustion event characterized by a second combustion characteristic substantially equal to the first combustion characteristic, and wherein the diesel injection pulse determined by the control system is unaffected by the second amount, the second timing, the third amount, and the third timing.   
     
     
         9 . The method of  claim 8 , wherein the first combustion characteristic comprises a torque generated by the engine. 
     
     
         10 . The method of  claim 8 , wherein the at least one operating parameter comprises one of vehicle speed, engine load, engine speed, intake temperature, and exhaust temperature. 
     
     
         11 . The method of  claim 10 , wherein the at least one operating parameter includes engine speed, and wherein determining the combined injection pulse includes determining the second amount, the second timing, the third amount, and the third timing based on the engine speed and the first amount. 
     
     
         12 . The method of  claim 8 , wherein the at least one operating parameter further includes at least one of intake air temperature and ambient air temperature, and wherein determining the combined injection pulse further includes determining the second amount, the second timing, the third amount, and the third timing based on the at least one of intake air temperature and ambient air temperature. 
     
     
         13 . The method of  claim 8 , further including
 sensing at least one of intake air temperature and ambient air temperature,   selecting, based on the at least one of intake air temperature and ambient air temperature, a set of look-up tables for use in determining the second amount, the second timing, the third amount, and the third timing,   determining the second amount, the second timing, the third amount, and the third timing with the set of look-up tables based on the first amount and an engine speed corresponding to the first amount.   
     
     
         14 . A dual fuel engine system, comprising:
 a sensor configured to determine at least one operating parameter associated with a dual fuel engine of the system;   a first controller in communication with the sensor, the first controller configured to determine a diesel injection pulse indicative of a first amount of diesel fuel to be injected into a combustion chamber of the engine and a first timing at which the first amount of diesel fuel is to be injected, wherein the diesel injection pulse is determined based on the at least one operating parameter and wherein fuel injection in accordance with the diesel injection pulse would result in a first combustion characteristic within the combustion chamber sufficient to satisfy an output demanded of the engine using solely diesel fuel; and   a second controller in communication with the first controller so as to receive information from the first controller without inhibiting operation of the first controller, the second controller configured to determine a combined injection pulse based on the diesel injection pulse, wherein the combined injection pulse is indicative of a second amount of diesel fuel to be injected different than the first amount, a second timing at which the second amount of diesel fuel is to be injected different than the first timing, a third amount of natural gas to be injected, and a third timing at which the third amount of natural gas is to be injected;   an injection system in communication with the second controller and fluidly connected to the combustion chamber, the injection system being configured to inject the second amount of diesel fuel and the third amount of natural gas into the combustion chamber in accordance with the combined injection pulse, wherein the injection in accordance with the combined injection pulse results in a combustion event characterized by a second combustion characteristic substantially equal to the first combustion characteristic, and wherein the diesel injection pulse determined by the first controller is unaffected by the second amount, the second timing, the third amount, and the third timing.   
     
     
         15 . The system of  claim 14 , wherein the sensor comprises a temperature sensor and the at least one parameter comprises at least one of intake air temperature and ambient air temperature, the system further configured to determine an engine speed corresponding to the first amount,
 the second controller being configured to select, based on the at least one of intake air temperature and ambient air temperature, a set of look-up tables stored in a memory of the second controller for use in determining the second amount, the second timing, the third amount, and the third timing, and   to determine, based on the first amount and the engine speed, the second amount, the second timing, the third amount, and the third timing using the set of look-up tables.