A passively Q-switched Nd:YAG/Cr4+:YAG micro-laser with three-beam output was realized. A single active laser source made of a composite, all-ceramics Nd:YAG/Cr4+:YAG monolithic cavity was pumped by three independent lines. At 5 Hz repetition rate, each line delivered laser pulses with ~2.4 mJ energy and 2.8-MW peak power. The M2 factor of a laser beam was 3.7, and stable air breakdowns were realized. The increase of pump repetition rate up to 100 Hz improved the laser pulse energy by 6% and required ~6% increase of the pump pulse energy. Pulse timing of the laser-array beams can by adjusted by less than 5% tuning of an individual line pump energy, and therefore simultaneous multi-point ignition is possible. This kind of laser can be used for multi-point ignition of an automobile engine.

Composite, all-ceramics, high-peak power Nd:YAG/Cr 4+ :YAG monolithic micro-laser with multiple-beam output for engine ignition

Performance of future ignition system for internal combustion engines should be reliable and efficient to enhance and sustain combustion stability, since ignition not only initiates combustion but also influences subsequent combustion. Lean burn systems have been regarded as an advanced combustion approach that could improve thermal efficiency while reducing exhaust gas emissions. However, current engines cannot be operated sufficiently lean due to ignition related problems such as the sluggish flame initiation and propagation along with potential misfiring. A high exhaust gas recirculation engines also has similar potential for emissions improvement, but could also experience similar ignition problems, particularly at idle operation. Similarly, ignition is an important design factor in gas turbine and rocket combustor. Recently, non-conventional ignition techniques such as laser-induced ignition methods have become an attractive field of research in order to replace the conventional spark ignition systems. The fundamentals of conventional laser-induced spark ignition have been previously reviewed. Therefore, the objective of this article is to review progress on the use of such innovative techniques of laser-induced ignition including laser-induced cavity ignition and laser-induced multi-point ignition. In addition, emphasis is given to recent work to explore the feasibility of this interesting technology for practical applications concerning internal combustion engines.

Review and recent developments of laser ignition for internal combustion engines applications

Numerical simulation of hydrogen combustion process in rotary engine with laser ignition system

Laser ignition (LI) has been shown to offer many potential benefits compared to spark ignition (SI) for improving the performance of internal combustion (IC) engines. This paper outlines progress made in recent research on laser ignited IC engines, discusses the potential advantages and control opportunities and considers the challenges faced and prospects for its future implementation. An experimental research effort has been underway at the University of Liverpool (UoL) to extend the stratified speed/load operating region of the gasoline direct injection (GDI) engine through LI research, for which an overview of some of the approaches, testing and results to date are presented. These indicate how LI can be used to improve control of the engine for: leaner operation, reductions in emissions, lower idle speed and improved combustion stability.

Laser ignited engines: progress, challenges and prospects

Laser ignition - Spark plug development and application in reciprocating engines

A robust, miniaturized, diode-pumped high-energy neodymium doped yttrium aluminium garnet (Nd:YAG) laser with passive Q-switch generating 25 mJ at 3 ns has been demonstrated at repetition rates of up to 150 Hz The device is designed for ignition of fuel air mixtures in internal combustion engines The pump diodes and Peltier cooling are integrated in the laser head, giving a compact design with a small number of optical components for easy assembly The laser was successfully operated as an optical spark plug on a test engine at high temperature and vibration levels

Novel miniaturized high-energy Nd-YAG laser for spark ignition in internal combustion engines

The laser has a pulsed pumped light source (30) formed by pumping diodes (3). A solid laser crystal is enclosed into a resonator (9), and a quality switch increases power density. A focusing device (7) focuses a Peltier cooling section (12) to a cooling mechanism (11) for cooling the resonator. The mechanism has cooling systems, where the Peltier cooling section is assigned to one of the cooling systems for cooling the diodes.

Gerhard Kroupa

Papers

Novel miniaturized high-energy Nd-YAG laser for spark ignition in internal combustion engines

Q-switched pumped solid-state laser