Current emission regulations relating to NOx require reciprocating engines to operate at very lean fuel/air mixtures. The excess air keeps the combusting gases cooler and limits thermal NOx development. At the same time, the lean mixture requires much more energy to be delivered to the spark plug for successful ignition. The higher energy flowing through the spark plug electrodes increases erosion to the point that the spark plugs last only hundreds of hours; they also cost more than $100 each because of the rare earth metals used to extend their life. The resulting maintenance costs are very high, especially for natural-gas-fueled energy generation engines that must run continuously for thousands of hours.
Researchers have explored the possibility of substituting a fiber-optics system capable of transmitting a laser-induced plasma spark to an ignition chamber, thereby eliminating the need for spark plugs. But the high energies needed to produce a plasma spark usually destroy the optical fiber. A fiber of sufficient diameter to handle the energy and resist destruction produces a laser spot so diffuse that it is incapable of generating a spark.
This challenge was met by combining a low-power optical pumping source, an optical distributor, and a number of distinct spark generators. The optical pumping source, having a peak optical power less than 1,000 Watts so as not to destroy the optical fibers, is coupled to the optical distributor. The distributor is connected to a number of spark generators that can produce a high-energy spark from the original low-power laser pulse.
The laser spark generators may be laser oscillators comprising a high-reflectivity mirror, a Q-switch, a laser media, an output coupler, and a lens. The optical pumping source is optically connected to the laser media, which is made of a material that emits a lasing energy when exposed to energy from the optical pumping source. The mirror is reflective to the lasing energy and positioned adjacent to and optically connected to the Q-switch or the laser media along a pumping axis. The Q-switch is adjacent to and optically connected to the laser media along the pumping axis. The laser media or the Q-switch is adjacent to and optically connected to the output coupler along the pumping axis. The output coupler is adjacent to and optically connected to the lens along the pumping axis.