NOVELTY - The system has a first electronic control unit (ECU) (102) for controlling delivery of supply amounts of first fuel and supplying amounts of second fuel for combustion within a multiple-fuel engine (100). The ECU includes inputs (172) to receive data identifying operating characteristics. A diesel oxidation catalyst (DOC) (136) is installed within an exhaust system of the engine, where the second fuel is substitute for amount of the first fuel, and is injected as vapors into an air intake system of the multiple-fuel engine prior to entering a combustion chamber of the multiple-fuel engine.    USE - System for converting a single-fuel engine(claimed) i.e. internal combustion engine, to a multiple-fuel engine e.g. stationary engine and mobile engine, using fuels e.g. diesel fuel, compressed natural gas, butane, biofuel and liquid petroleum gas such as propane e.g. HD-1O propane for a vehicle i.e. semi-tractor.    ADVANTAGE - The DOC reduces undesired exhaust emissions of the engine. The system allows backpressure sensors for maintaining engine exhaust backpressure within pre-conversion range of exhaust backpressures. The system facilitates arrangement of a mixer pin assembly within the air intake system to cause the air within the air intake system to tumble, thus improving mixing of the air and the fuel exiting the orifices of the mixer pin assembly. The system allows the second fuel to be consumed, while the engine operates in the multiple-fuel mode, so that the first fuel need not be consumed while the engine operates in the multiple-fuel mode, thus operating the engine in the multiple-fuel mode and reducing the amount of first fuel used to operate the engine. The system controls the amount of fuel used by the engine, so that over-fueling of the engine can be prevented and harmful exhaust emissions do not exceed emission limits, thus avoiding engine damage. The DOC reduces level of certain emissions emitted by the engine, while the engine operates in a single or multiple-fuel mode. The system converts the engine into a multiple-fuel engine without installation of a spark ignition system, so that cost of an engine conversion system is made less as compared to the engine conversion system with the spark ignition system.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) an energy conversion system configured for conversion of an engine from a single-fuel engine using afirst fuel to multiple-fuel engine using the first fuel and a second fuel    (2) a multiple-fuel engine produced by converting a single fuel engine to a multiple fuel engine.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of a multiple-fuel engine.    Multiple-fuel engine (100)    ECU (102)    DOC (136)    Telemetry module (170)    Inputs (172)    Telemetry user-device (174)    Engine block (190)