the following description is merely exemplary in nature and is not intended to limit the present disclosure , application , or uses . for purposes of clarity , the same reference numbers will be used in the drawings to identify similar elements . as used herein , the term module refers to an application specific integrated circuit ( asic ), an electronic circuit , a processor ( shared , dedicated , or group ) and memory that execute one or more software or firmware programs , a combinational logic circuit , or other suitable components that provide the described functionality . referring now to fig1 , an exemplary hybrid vehicle 10 is schematically illustrated . the hybrid vehicle 10 includes an engine 12 and an electric machine 14 , which selectively drive a transmission 16 . hybrid vehicle 10 may be a plug - in type hybrid vehicle or any other type of hybrid vehicle that is capable of extended periods of operation without operation of engine 12 . engine 12 is in communication with a source of fuel , such as fuel tank 18 and an on - board vapor recovery canister 19 in communication with fuel tank 18 . in one mode of vehicle operation , the electric machine 14 and the engine 12 provide drive torque to drive the transmission 16 . in this manner , fuel efficiency may be increased and emissions may be reduced . in another mode of operation , the engine 12 drives the electric machine 14 to generate power used to recharge an energy storage device ( esd ) 20 , such as a battery . in another mode of operation , the electric machine 14 solely provides drive torque to the transmission 16 using energy from the esd 20 . in yet another mode of operation , the engine 12 may solely provide the requisite drive torque to the transmission 16 . the engine 12 and the electric machine 14 can be coupled via a belt - alternator - starter ( bas ) system ( not shown ) that includes a belt and pulleys . alternatively , the engine 12 and the electric machine 14 can be coupled via a flywheel - alternator - starter ( fas ) system ( not shown ), wherein the electric machine 14 is operably disposed between the engine 12 and the transmission 16 . it is anticipated that other systems can be implemented to couple the engine 12 and the electric machine 14 including , but not limited to , a chain or gear system that is implemented between the electric machine 14 and a crankshaft . the transmission 16 can include , but is not limited to , a continuously variable transmission ( cvt ), a manual transmission , an automatic transmission , an electrically variable hybrid transmission , and an automated manual transmission ( amt ). drive torque is transferred from the engine 12 and / or electric machine 14 to the transmission 16 through a coupling device 22 . the coupling device 22 can include , but is not limited to , a friction clutch or a torque converter depending upon the type of transmission implemented . in the case of a cvt , the coupling device 22 includes a torque converter and a torque converter clutch ( tcc ). the transmission 16 multiplies the drive torque through one of a plurality of gear ratios to drive a vehicle driveline ( not shown ). a control module 24 regulates operation of the vehicle 10 based on the control system of the present disclosure . a current sensor 26 generates a current signal that is sent to the control module 24 and a voltage sensor 28 generates a battery voltage signal that is sent to the control module 24 . the control module 24 determines a state of charge ( soc ) of the esd 20 based on the current and voltage signals . there are several methods that can be implemented to determine the soc . an exemplary method is disclosed in commonly assigned u . s . pat . no . 6 , 646 , 419 , issued on nov . 11 , 2003 and entitled state of charge algorithm for lead - acid battery in a hybrid electric vehicle , the disclosure of which is expressly incorporated herein by reference . control module 24 may signal operation of the engine 12 when required , as discussed below . control module 24 may provide and / or receive signals for operation of a fuel pump 30 when operation of engine 12 is required . control module 24 may receive signals from vehicle sensors 32 , such as ambient temperature , and signals from a fuel level sender 34 indicative of a fuel level in fuel tank 18 . control module 24 may provide a signal to a vehicle display 36 indicative of vehicle operating conditions such as fuel age and elapsed time between engine operations . with additional reference to fig2 , control module 24 may include a fuel fill module 38 , a fuel age module 40 , a fuel quality module 42 , an engine last start module 44 , an oil deterioration by fuel dilution module 45 , a vapor recovery canister loading module 47 , and an engine operation module 46 . the fuel fill module 38 may determine whether fuel has been added to fuel tank 18 and the quantity added . fuel fill module 38 is in communication with fuel age module 40 . fuel age module 40 may determine an age of the fuel in fuel tank 18 . the fuel age determination may be at least partially based on the fuel fill information provided by fuel fill module 38 . fuel age module 40 is in communication with engine operation module 46 and fuel quality module 42 . fuel quality module 42 may determine a deterioration level of the fuel in fuel tank 18 . the determination of fuel deterioration level may be at least partially based on the fuel age information provided by fuel age module 40 and ambient storage temperature from vehicle sensors . fuel quality module 42 may receive and evaluate information relating to fuel type , such as gasoline or ethanol blends , and provide a signal to engine operation module 46 to operate the engine 12 at the next vehicle start - up . engine last start module 44 may determine the elapsed time between consecutive operations of engine 12 . engine last start module 44 is in communication with engine operation module 46 . oil deterioration by fuel dilution module 45 may be in communication with engine operation module 46 . oil deterioration by fuel dilution module 45 may determine the condition of engine lubricating oil based on a fuel dilution level thereof . vapor recovery canister loading module 47 may be in communication with engine operation module 46 . vapor recovery canister loading module 47 may determine the canister loading through vehicle driving statistics and temperature information . engine operation module 46 may determine whether engine - on operation is required . as seen in fig3 , the flow chart illustrates control logic 100 providing a method of controlling hybrid vehicle 10 . once vehicle 10 has been powered on , determination block 101 determines whether a manual engine - start override is desired . if a manual engine - start override is desired , an engine start flag set and stored in control module 24 during a previous iteration may be reset at control block 103 . control logic 100 may then proceed to determination block 102 . if a manual engine - start override is not desired , control logic 100 may proceed to determination block 102 . determination block 102 evaluates whether an engine start flag was set and stored in control module 24 during a previous operation of vehicle 10 . if an engine start flag was previously set , control logic 100 proceeds to control block 104 , where engine 12 is automatically started . engine 12 may then be operated for a predetermined period of time . control logic 100 then proceeds to control block 106 , where the driver of vehicle 10 is notified of the reason for the engine start . after notification , control logic 100 proceeds to control block 108 . referring to determination block 102 , if no flag was set during previous operation of vehicle 10 , control logic 100 proceeds to control block 108 as well . control block 108 determines the type of fuel used in vehicle 10 . this determination may be based on an input from a sensor or a driver input . once the fuel type is determined , control logic 100 proceeds to determination block 110 . determination block 110 evaluates whether fuel has been added to fuel tank 18 . if fuel has been added , control logic 100 proceeds to control block 112 where a fuel age is reset within control module 24 to an adjusted value . control logic 100 then proceeds to control block 114 . if fuel has not been added , control logic 100 proceeds to control block 114 as well . control block 114 determines a fuel quality level indicated by an age and deterioration level of the fuel . fuel age and deterioration level may be determined based on a number of inputs including ambient temperature measurements from vehicle sensors 32 , calibration values , fuel tank level measurements from fuel level sender 34 , elapsed time between fuel fills and the amount of fuel added during fuel fills . each of these inputs may be stored within or provided to control module 24 . control logic 100 then proceeds to control block 116 . control block 116 determines operating criteria for engine 12 . specifically , control block 116 begins with a nominal set of engine - on criteria . these criteria may include operating engine 12 when the load on esd 20 exceeds a predetermined value or when the state of charge of esd 20 falls below a predetermined level . using the fuel age and deterioration level , or fuel quality level , determined at control block 114 , engine - on operating criteria may be biased toward an engine - on condition . for example , the values of maximum load on esd 20 and the minimum charge level required prior to an engine - on condition may be adjusted to increase the occurrence of an engine - on condition . this may reduce the overall time that fuel will remain in fuel tank 18 unused . control logic 100 may then proceed to control block 118 . control block 118 notifies the driver of a fuel age . the notification may include an indication of the amount of time since fuel was last used or some other indication of fuel aging . control logic 100 then proceeds to determination block 120 . determination block 120 evaluates whether an elapsed time between engine - on conditions has exceeded a predetermined limit . engine 12 may require a certain frequency of operation to ensure proper lubrication and corrosion control . if the elapsed time between engine - on conditions has exceeded a predetermined time limit , control logic 100 proceeds to control block 122 where an engine start flag is set . the engine start flag may be stored by control module 24 and may initiate an engine - on condition during a subsequent vehicle use when detected at determination block 102 . alternatively , the engine start flag may initiate an engine - on condition automatically when set . control logic 100 may then proceed to determination block 124 . at determination block 120 , if the elapsed time between engine starts does not exceed the predetermined limit , control logic 100 also proceeds to determination block 124 . determination block 124 evaluates whether a fuel age has exceeded a predetermined limit . if the fuel age has exceeded the predetermined time limit , control logic 100 proceeds to control block 126 where an engine start flag is set . the engine start flag may initiate an engine - on condition during a subsequent vehicle operation when detected at determination block 102 . control logic 100 may then proceed to determination block 128 . at determination block 124 , if fuel age does not exceed the predetermined limit , control logic also proceeds to determination block 128 . determination block 128 evaluates whether the oil is diluted by fuel beyond a predetermined limit . if the oil dilution has exceeded the predetermined limit , control logic 100 proceeds to control block 130 where an engine start flag is set . the engine start flag may initiate an engine - on condition during a subsequent vehicle operation when detected at determination block 102 . control logic 100 may then proceed to determination block 132 . if the oil dilution has not exceeded the predetermined limit , control logic 100 also proceeds to determination block 132 . determination block 132 evaluates whether the vapor canister is loaded by fuel vapor beyond a predetermined limit . if the vapor loading has exceeded the predetermined limit , control logic 100 proceeds to control block 134 where an engine start flag is set . the engine start flag may initiate an engine - on condition during a subsequent vehicle operation when detected at determination block 102 . alternatively , the engine start flag may initiate an engine - on condition automatically when set . control logic 100 may then terminate . if the vapor loading has not exceeded the predetermined limit , control logic 100 may terminate . those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms . therefore , while this disclosure has been described in connection with particular examples thereof , the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings , the specification and the following claims .