Development of Advanced Laser Ignition System for Stationary Natural Gas Reciprocating Engines

Abstract

Laser ignition is considered the prime alternative to conventional coil based ignition for improving efficiency and simultaneously reducing NOx emissions in lean-burn natural gas fired stationary reciprocating engines. In this paper, Argonne’s efforts towards the development of a viable laser ignition system are presented. The relative merits of various implementation strategies for laser based ignition are discussed. Finally, the performance improvements required for some of the components for successful field implementation are listed. Also reported are efforts to determine the relative merit of laser ignition over conventional Capacitance Discharge Ignition (CDI) ignition. Emissions and performance data of a large-bore single cylinder research engine are compared while running with laser ignition and the industry standard CDI system. It was primarily noticed that NOx emissions reduce by 50% under full load conditions with up to 65% reductions noticed under part load conditions. Also, the lean ignition limit was significantly extended and laser ignition improved combustion stability under all operating conditions. Other noticeable differences in combustion characteristics are also presented. Efforts wherein ignition was achieved while transmitting the high-power laser pulses through optical fibers showed performance improvements similar those achieved by using free-space laser ignition.

Natural Gas Fired Reciprocating Engines for Power Generation: Concerns and Recent Advances

“…Weinrotter, Herdin et al [34] have tried to develop a split system wherein a long laser pulse from a pump laser is transmitted through a optical fiber to end pump a laser gain medium equipped with a saturable absorber installed in the spark plug well of the engine. Bihari et al through their attempts found it difficult to transmit high-power laser pulses through optical fibers and have embarked in developing a system that uses free-space transmission [31]. Recently, Taira et al [35,36] have successfully demonstrated microlaser ignition systems, by using new age lasing materials called optical ceramics, and by using pulse trains of low-energy pulses to ignite instead of a single high-energy laser pulse.…”

“…[22] Laser ignition tests performed in natural gas fueled single-cylinder engines have shown (i) shorter ignition delays, (ii) accelerated rates of combustion, and (iii) lean ignition limit extensions. However, as shown in Figure 20, the most significant advantage is the fact that laser ignition can result in NOx reductions up to 70% for a given engine efficiency, or alternately up to 3% point improvement in efficiency for a given NOx level [31]. The associated cost savings due to reduced fuel consumption, and avoidance of expensive after treatment systems, have provided an impetus for the development of practical laser ignition systems.…”

“…BSNOx vs. thermal efficiency improvement with laser ignition. [31] The earliest known attempt at laser ignition was that performed by Dale et al in 1978 [32], when they used a 14 ft. long CO2 laser. At that time, laser ignition was considered impractical due to the high-cost and large size of the lasers, and interest in laser ignition remained luke warm.…”

Multi-zone modelling of partially premixed low-temperature combustion in pilot-ignited natural-gas engines

“…Of these, pilot ignition, which uses small diesel sprays as the ignition sources, offers the advantages of multiple ignition centres and higher energy densities compared with conventional spark ignition. Gebert et al [9] showed that the energy associated with a pilot diesel spray volume of 1 mm 3 is approximately two orders of magnitude greater than the energy provided by a spark. Therefore, the quality of ignition is better with diesel pilot ignition, and spatially dispersed, multiple-ignition centres lead to faster burn rates compared to singlepoint ignition sources.…”

“…However, the challenge with employing natural gas as an engine fuel stems from the fact that it is primarily composed of methane, which is very difficult to ignite. Several ignition strategies including lean-burn spark ignition [1], laser ignition [2,3], and pilot ignition [4][5][6][7][8] have been utilized to increase efficiencies and to decrease emissions from natural-gas engines. Of these, pilot ignition, which uses small diesel sprays as the ignition sources, offers the advantages of multiple ignition centres and higher energy densities compared with conventional spark ignition.…”