In 2003, NASA Marshall tested a dual-pulse laser ignition system for rocket engines; a separate microgravity study examined laser ignition and flame spread in solid fuel

In 2003, engineers at NASA's Marshall Space Flight Center tested a dual-pulse laser ignition system for rocket engines on the ground, as documented in the NASA Technical Reports Server study, Evaluation and Characterization Study of Dual Pulse Laser-Induced Spark (DPLIS) for Rocket Engine Ignition System Application (NTRS ID 20030067733). The work examined whether laser sparks could provide a practical ignition method for rocket propellants. Separate microgravity experiments later examined how ignition and flame spread over solid fuels changed when buoyancy was greatly reduced, as shown in Localized Ignition and Subsequent Flame Spread Over Solid Fuels in Microgravity, a NIST-affiliated study archived on the NASA Technical Reports Server (NTRS ID 20040053565).

NASA Marshall tested dual-pulse laser ignition for rocket engines in 2003

Evaluations and characterizations study on Dual-Pulse Laser Induced Spark (DPLIS) as an Ignition System for Rocket Engine Applications described the use of a dual pulse laser in rocket engine ignition. Characterization experiments for the dual-pulse system were conducted using gaseous hydrogen and air in a Hencken burner, with the results intended to help optimize the laser format for future testing in a subscale H₂/O₂ rocket chamber.


NASA technical reports server study

In the dual-pulse laser system, the energy was split between two pulses instead of being delivered in a single pulse. The first pulse generated the plasma while the second one interacted with the generated plasma. Results indicated that splitting the energy can produce a plasma with a longer lifetime and efficient laser energy absorption. The dual-pulse system produced a spark that was better for ignition than a single pulse with the same energy level. This was in the case of lean hydrogen and air. The test examined pulse spacing, laser energy and plasma behavior to identify the best ignition conditions.

The dual-pulse system reduced the peak power needed for fibre-optic delivery

The Marshall scientists also considered using fiber-optic coupling to deliver laser energy into the combustion chamber. By keeping the laser generator outside the combustion chamber, the design could be simpler; however, delivering a high-energy laser pulse through optical fibers imposed a peak-power limit. The dual-pulse concept provided a solution to this problem, since the spreading of energy over two pulses decreased the amount of power required to be delivered by the fiber optics. This approach was well suited to setups where the laser generator and combustion chamber were separated. The same investigation thus analyzed both the properties of the laser-generated plasma and the practicalities of energy delivery to the rocket engine.

A separate microgravity experiment tested CO₂ laser ignition of PMMA

The microgravity study used an entirely separate experimental setup and fuel source. Titled Localized Ignition and Subsequent Flame Spread Over Solid Fuels in Microgravity, it examined ignition and flame spread in polymethyl methacrylate, or PMMA, using CO₂ lasers. The experiment was performed at the 10-second drop tower of the Japan Microgravity Center (JAMIC).

The study examined ignition on the laser-exposed surface and on the opposite side of the material. Effects of material thickness and oxygen concentration on the ignition process were also studied. Ignition of the laser-irradiated surface occurred almost immediately, while ignition on the opposite surface took noticeably longer.

Reduced buoyancy affected heat and combustion-product transport

The microgravity experiment helped explain how reduced buoyant flow changes ignition behavior. On Earth, buoyancy makes hot air rise and creates flows that affect how heat and combustion products move around the ignition point. In microgravity, buoyant flows are greatly reduced, which can change how gases move, how heat spreads through the fuel, and how combustion products leave the burning area.

The Marshall and microgravity studies examined different ignition conditions

This difference is critical because the microgravity experiment was not conducted to study the rocket ignition system developed by Marshall. Instead, it was conducted to investigate how the surrounding gravitational field can affect the ignition process and flame propagation. In the Marshall study, the authors' interest was to develop an efficient ignition source and to find out an effective way to supply laser energy, while the microgravity experimenters were interested in the effects caused by low buoyancy.

Laser ignition research addressed both plasma formation and engine integration

Marshall’s experiment showed that laser ignition involved more than simply producing enough energy to create a spark. The synchronization of the two lasers affected the plasma dynamics, whereas the energy split between the two pulses affected the peak power needed for fiber-optic delivery. After ignition, the external environment could affect heat and combustion product transport and the development of a flame.