Free space optical spectrometer systems and methods for their use

A method for wavelength correction in a free space optical spectrometer system comprising the steps of:

• generating a laser beam that scans across a range of wavelengths;
• splitting the laser beam into a plurality of beams using a beam splitter;
• determining a sample spectrum from a first beam after it has passed through a sample fluid;
• determining a reference-free-space spectrum from a second beam after it has passed through only free space;
• determining a reference-cell spectrum from a third beam after it has passed through a reference material contained in a reference cell;
• determining an etalon spectrum from a fourth beam after it has passed through an etalon;
• performing dark current corrections on each of the spectra obtained from the first, second, third and fourth beams;
• calculating a wavelength offset between the reference-cell spectrum and a known spectrum for the reference material;
• determining a wavelength correction equation by flattening the etalon spectrum;
• performing wavelength correction on each of the dark current corrected spectra based on the wavelength offset and the wavelength correction equation;
• and
• determining a signal absorption spectrum for the sample spectrum based on the wavelength-corrected sample spectrum and the wavelength-corrected reference-free-space spectrum.

A engine system comprising:

• a first control valve positioned along a first supply line in fluid communication between a first fuel supply and a fuel input of an engine, the first control valve being configured to regulate a flow of a first fuel from the first fuel supply to the fuel input;
• a second control valve positioned along a second supply line in fluid communication between a second fuel supply and the fuel input, of the engine, the second control valve being configured to regulate a flow of a second fuel from the second fuel supply to the fuel input;
• a free-space optical spectrometer in fluid communication with the first supply line at a location between the first fuel supply and the first control valve, the spectrometer being configured to obtain spectroscopic measurements of the first fuel in near real time;
• and
• a control system operatively coupled to the spectrometer and to the first and second control valves, the control system being configured to determine one or more characteristics of the first fuel based on the spectroscopic measurements and to control actuation of at least one of the first control valve or the second control valve responsive to said determination.

A method of operating an engine comprising the steps of:

• flowing a first fuel to an engine;
• spectroscopically monitoring a characteristic of the first fuel;
• determining if the characteristic is outside of a predetermined parameter;
• modulating the flow of the first fuel to the engine based on said determination;
• and
• modulating a flow of a second fuel to the engine.