TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The method further involves catalytically converting the quenched synthesis gas into a long-chain hydrocarbon fluid through a Fischer-Tropsch processing unit; fractionating the long-chain hydrocarbon fluid into at least one useful product; introducing steam, or a tail gas in the fuel stream within the premixing device; recirculating a tail gas from the Fischer-Tropsch processing unit into the premixing device; and introducing steam into the fuel stream within the premixing device to enhance the flashback resistance. The preconditioning the fuel stream involves generating a swirl movement in the fuel stream through several swirler vanes, or accelerating the fuel stream to a desired velocity through a nozzle. The method involves introducing oxygen with a velocity component transverse and/or tangential to the fuel stream. Preferred Device: The flow conditioning device comprises several swirler vanes to provide a swirl movement to the fuel stream; several counter flow swirler vanes disposed adjacent and radially inward to the the swirler vanes; and a nozzle configured to accelerate the fuel stream to a desired velocity. The number of swirler vanes is 4-15, and a turning angle for each of the swirler vanes is 20-55degrees. The turning angle of each of the counter swirler vanes is relatively greater than the turning angle of each of the swirler vanes. The flow conditioning device is configured to introduce the fuel stream in the rich premixed natural gas combustion system, and oxygen is introduced in 1/2 portions by volume. The syngas generator comprises a rich premixed natural gas combustion system; and further comprises a first inlet configured to introduce steam, a second inlet configured to introduce carbon dioxide (CO2), a third inlet configured to introduce tail gas into the fuel stream, a fourth inlet configured to introduce oxygen through holes in the swirler vanes, or centerbody, and/or walls of the premixing device. The tail gas is recirculated into the fuel stream from a downstream process of a syngas generator. The temperature of the fuel stream is 400-1300 degreesF; and a temperature of the oxygen stream is 200-500degreesF. The ratio of an effective area of the oxygen inlet and an effective area of the flow conditioning device is 0.1-0.5. The premixing residence time of the syngas generator is 0.25-100 milliseconds. The oxygen inlet of the syngas generator and the gas to liquid system comprises several holes disposed on each of the swirler vanes, a center body, and/or walls of the premixing device. The oxygen inlet of the syngas generator is configured to introduce oxygen from the centerbody, outer wall with a velocity component transverse to the fuel flow; and/or through several holes in the swirler vanes with a velocity component transverse and/or tangential to the fuel flow. The fuel stream is introduced through an outer ring of holes disposed on the tip of the premixing device, and oxygen is introduced through an inner ring of holes disposed on the tip of the premixing device. The ratio of number of oxygen atoms to number of carbon atoms in the fuel stream in the premixing region is 0.6-1.6. The syngas generator comprises several oxygen inlets to facilitate staging of oxygen flow within the syngas generator to enable substantially stable combustion. The combustion chamber of the syngas generator and gas to liquid system is treated with a catalytic surface to promote syngas formation. The gas to liquid system of further comprises: a Fischer-Tropsch processing unit for receiving quenched synthesis gas and for catalytically converting the quenched synthesis gas into a long-chain hydrocarbon fluid; and an upgrading unit for fractionating the long-chain hydrocarbon fluid into at least one product selected from synthetic diesel fuel, synthetic kerosene, ethanol, dimethyl ether, and/or naptha. The fuel stream of the gas to liquid system comprises natural gas; natural gas and tail gas; natural gas and steam; natural gas, tail gas and steam; natural gas, tail gas and CO2; natural gas, tail gas, steam, and CO2; or natural gas, steam, and CO2. The flow conditioning device of the gas to liquid system comprises several swirler vanes to provide a swirl movement to the fuel stream, or a nozzle configured to accelerate the fuel stream to a desired velocity. The premixing device of the gas to liquid system further comprises a first inlet configured to introduce steam into the fuel stream, a second inlet configured to introduce a tail gas into the fuel stream, a third inlet configured to introduce CO2 into the fuel stream, and a fourth inlet configured to introduce an O2 stream downstream of the fuel flow conditioning device to facilitate premixing.