Laser Spark Plug Research Articles

Laser ignition of hydrogen/air mixtures in a constant-volume combustion chamber using a pulse-burst Nd:YAG/Cr4+:YAG laser spark plug

In this study, characteristics of laser ignition of H2/air mixtures are investigated in a constant-volume combustion chamber using a compact, passively Q-switched Nd:YAG/Cr4+:YAG laser spark plug. Ignition was conducted at a single point, with precise timing achieved through two laser modes of operation: delivering a single laser pulse and operating in pulse-burst mode, emitting trains of up to five laser pulses. Experiments covered a wide range of relative equivalence ratios (λ= 1.5 to 5.0) at 1 bar initial pressure and extended to 9 bar. Under similar pressure conditions, igniting H2/air mixtures with higher λ values (lean mixtures) results in a reduction of maximum pressure and a slower combustion process. Conversely, maintaining the same λ value for H2/air mixtures, while elevating the initial pressure, yields higher maximum pressures, but concurrently decelerates the combustion process. Pulse-burst mode laser ignition expedited combustion, especially for lean mixtures (λ> 4.0), showcasing advantages over single-pulse laser ignition. Additionally, lean ignition limits were determined at different pressures, revealing pressure-dependent differences between single pulse and pulse-burst modes laser ignition. These results provide insights into the features of laser ignition with pulse trains of H2/air mixtures and the use of this ignition technique in hydrogen-powered reciprocating engines.

Combustion and Flame Propagation Characteristics of Laser Spark Plug Ignited Methane/Air Mixtures in a Constant Volume Combustion Chamber

Combustion and Flame Propagation Characteristics of Laser Spark Plug Ignited Methane/Air Mixtures in a Constant Volume Combustion Chamber

Comparison of laser ignition and spark plug by thermodynamic simulation of multi-zone combustion for lean methane-air mixtures in the internal combustion engine

Usage of the laser ignition system can potentially solve most of the combustion issues, for instance, low flame velocity, imperfect combustion, and improve the lean-burn limit. In the present study, the ultimate purpose is to investigate the combustion of methane and lean air mixture in an internal combustion engine by laser ignition. Using quasi-dimensional and multi-zone approach, the engine thermal performance parameters for laser ignition and spark plug have been compared. One of the main results obtained is that the use of laser ignition in comparison with the spark plug for methane and air mixture reduces combustion duration at different equivalence ratios. The use of laser ignition improved thermal efficiency by 8.13%, the average pressure by 10%, specific fuel consumption by 27.44%, and the maximum pressure by 37.83% compared to compression spark plug for an equivalence ratio of 0.7. Also, the result of the use of spark plug for the mixture of methane and air with an equivalence ratio of 0.6 was part of the total mixture remaining unburnt, and as the piston approached the BDC position, the unburned mixture remained in the cylinder, while the usage of laser ignition solved this challenge.

Comparison of laser breakdown and laser ablation ignition thresholds of combustible gas mixtures

One of the strong advantages stated for laser spark plugs is the ability to ignite fuel lean mixtures resulting in improved fuel economy and reduced NO x emission. However, lean mixtures demand high laser pulse energies for ignition. That could be overcome by using laser ablation rather than optical breakdown plasma to establish the combustion core. For fuel equivalence ratios ϕ ≈ 0.4–1.3, we have experimentally compared ignition thresholds for these two cases at pressures of p ≈ 1–3 bar of a butane-based combustible mixture. Our results show that laser pulse energy for fuel lean mixtures ignition can be significantly (by more than an order of magnitude) reduced using the ablator (stainless steel SS304) as compared to optical breakdown.

Comparative research results of CFR Octane Rating Unit Engine and Dacia Single Cylinder SI Engine equipped with classical Spark Plug and LASER Ignition

Nowadays, research has developed new technologies for a better control of the combustion process. Among the new technologies used for Ignition and combustion control, the LASER spark plug system is defined as an innovative technology which could overcome several limitations of classical spark plug. The purpose of the paper is the experimental research of the LASER spark plug used in the spark ignition(SI) engine. Improved performance, ensuring rapid and robust combustion, depends on how the Ignition stage is achieved. An Ignition system that could provide such an enhanced combustion process is the one based on plasma generation using a Q switched solid state LASER that delivers pulses with high MW peak power. The LI device used in the current research was a LASER medium Nd:YAG/Cr4+:YAG ceramic structure (Baikowski Co., Japan) that consisted of a 8.0-mm long, 1.0-at.% Nd:YAG ceramic, optically-bonded to a Cr4+:YAG ceramic with saturable absorption. It was designed, integrated and built to resemble a classical Spark Plug and could be mounted directly on the cylinder of a CFR Octane Rating Unit Engine as well as on a Dacia Single Cylinder SI Engine which led to several results among which: indicated, mediated pressures and their wave dispersion.

Research of CFR SI Engine and Dacia single cylinder SI engine equipped with LASER and Classical Spark Plug

Latest investigation has shown that laser ignition offers many potential benefits compared to the classical spark plug ignition due to the improvement of the performance of internal combustion engines. This paper aims to show the progress made in recent research on laser ignited internal combustion engines and also discusses the advantages and control opportunities, while considering the challenges faced and the prospects for its future implementation. It has been demonstrated that laser ignition can be used to improve the control of the engine in areas such as improved combustion stability, reductions in emissions, lower idle speed and leaner operation. Moreover, laser ignition not only that is non-invasive, but it also has a great flexibility in terms of the ignition position. Therefore, it allows the possibility of multi-point ignition. On the other hand, spark plugs offer limited possibilities for optimising engine efficiency, as their fixed position within a cylinder and the protrusion of electrodes disturbs the cylinder geometry and can also quench the flame kernel. As a result, this paper explores several results of the recent research focusing on: indicated, mediated pressures and their wave dispersion.

On the improvement by laser ignition of the performances of a passenger car gasoline engine.

Laser ignition was used to operate a four-stroke, four-cylinder, multipoint fuel injection gasoline passenger car engine, replacing the engine classical ignition device. The laser ignition system was compactly built with diode end-pumped Nd:YAG/Cr4+:YAG composite ceramics, each laser spark plug delivering pulses at 1.06 μm with 4 mJ energy and 0.8ns duration at variable repetition rate, in accordance with the engine speed. The engine was operated at constant speed-constant load condition of 2000 rpm-2 bar equivalent brake mean effective pressure, and different ignition timings, thus simulating city traffic situations. Two relative air-fuel ratios have been considered: λ~1 for the stoichiometric mixture operation and λ~1.25 for the lean mixture condition. Parameters indicating engine performance, efficiency, combustion stability, and emissions have been measured and registered when groups of 500 consecutive cycles were acquired. The engine brake power, brake specific fuel consumption, coefficient of variability for indicated mean effective pressure, initial and main combustion stage durations, as well as exhaust emissions like carbon monoxide (CO) and total unburned hydrocarbons (THC) emphasized that significant improvements can be obtained for lean air-fuel mixture operation. Increases of the nitrogen oxides emission (NOx) were measured when laser ignition was used.

Performances of a Research CFR Octane Rating Unit Engine and Dacia Single Cylinder SI Engine Ignited by a LASER System

At this time, the severe legislation regarding the level limits of the waste and exhaust gases released by thermal engines and also the necessity of engines efficiency improvement boost the engine research domain to bring in front the use of new technologies that can be used to control the in-cylinder combustion process. Now, the new technologies is represented by LASER spark plug systems which can be successfully used at petrol engines. LASER spark plug technology can have many advantages for engine operation control, an ignition system that could provide improved combustion is the one using plasma generation and a Q-switched LASER that results in pulses with high MW power. The LASER spark plug device used in the current research was a LASER medium Nd:YAG/Cr4+:YAG ceramic structure made up of a 8.0-mm long, 1.0-at.% Nd:YAG ceramic, optically-bonded to a Cr4+:YAG c. It was developed and constructed similar to classical spark plug and could be assembled on a CFR Octane Rating Unit Engine as well as on a Dacia Single Cylinder SI Engine which led to several results among which: influences on in-cylinder pressure, combustion and pollutant emissions.

Research of CFR SI Engine and Dacia single cylinder SI engine equipped with LASER and Classical Spark Plug

Research of CFR SI Engine and Dacia single cylinder SI engine equipped with LASER and Classical Spark Plug

Laser ignition of liquid petroleum gas at elevated pressures

Recent development of laser spark plugs for internal combustion engines have shown lack of data on laser ignition of fuel mixtures at multi-bar pressures needed for laser pulse energy and focusing optimisation. Methane and hydrogen based mixtures are comparatively well investigated, but propane and butane based ones (LPG), which are widely used in vehicles, are still almost unstudied. Optical breakdown thresholds in gases decrease with pressure increase up to ca. 100 bar, but breakdown is not a sufficient condition for combustion ignition. So minimum ignition energy (MIE) becomes more important for combustion core onset, and its dependency on mixture composition and pressure has several important features. For example, unlike breakdown threshold, is poorly dependent on laser pulse length, at least in pico- and to microsecond range. We have defined experimentally the dependencies of minimum picosecond laser pulse energies (MIE related value) needed for ignition of LPG based mixtures of 1.0 to 1.6 equivalence ratios and pressure of 1.0 to 3.5 bar. In addition to expected values decrease, low-energy flammability range broadening has been found at pressure increase. Laser ignition of LPG in Wankel rotary engine is reported for the first time.

Pulse train ignition with passively Q-switched laser spark plugs

Leaner burning and downsizing are two concepts pursued by engine developers to reduce fuel consumption and emissions. Both approaches lead to increasing challenges concerning ignition, as these concepts are typically associated with an increase in flow velocity and degree of turbulence as well as raised pressure at the moment of ignition. In this context, the use of miniaturized passively Q-switched laser spark plugs with pulse train ignition is considered as a promising alternative to conventional spark plugs. However, the application of these passively Q-switched laser spark plugs inevitably leads to the question of optimum pulse train parameters. For a better understanding, this study deals with improved flame formation by passively Q-switched laser pulse train ignition under engine-like conditions. The entire ignition process is investigated with a special focus on interactions of consecutive pulses. Therefore, three methods are combined: energy transfer measurements from laser pulse to plasma with high temporal and spatial resolution show the breakdown process depending on different pressures and fluid mixtures. The temperature decrease in the induced plasma is analyzed with measurement strategies for temporal high-resolved plasma spectroscopy especially adapted to passively Q-switched lasers. In combination with high-speed schlieren measurements, the changing local ignition conditions during pulse train ignition are demonstrated. The experiments show how consecutive pulses interact and contribute to the ignition in case of a gas flow. The used prototypes of laser spark plugs are provided by Robert Bosch GmbH.

Characterization of energy transfer for passively Q-switched laser ignition

Miniaturized passively Q-switched Nd:YAG/Cr(4+):YAG lasers are promising candidates as spark sources for sophisticated laser ignition. The influence of the complex spatial-temporal pulse profile of such lasers on the process of plasma breakdown and on the energy transfer is studied. The developed measurement technique is applied to an open ignition system as well as to prototypes of laser spark plugs. A detected temporal breakdown delay causes an advantageous separation of plasma building phase from energy transfer. In case of fast rising laser pulses, an advantageous reduction of the plasma breakdown delay occurs instead.

Lean-Burn Stationary Natural Gas Engine Operation With a Prototype Laser Spark Plug

An end pumped passively Q-switched laser igniter was developed to meet the ignition system needs of large bore lean burn stationary natural gas engines. The laser spark plug used an optical fiber coupled diode pump source to axially pump a passively Q-switched Nd:YAG laser and transmit the laser pulse through a custom designed lens. The optical fiber coupled pump source permits the excitation energy to be transmitted to the spark plug at relatively low optical power, less than 250 W. The Q-switched laser then generates as much as 8 mJ of light in 2.5 ns, which is focused through an asymmetric biconvex lens to create a laser spark from a focused intensity of approximately 225 GW/cm2. A single cylinder engine fueled with either natural gas only or hydrogen augmented natural gas was operated with the laser spark plug for approximately 10 h in tests spanning 4 days. The tests were conducted with fixed engine speed, fixed boost pressure, no exhaust gas recirculation, and laser spark timing advance set at maximum brake torque timing. Engine operational and emissions data were collected and analyzed.

Laser-induced optical breakdown applied for laser spark ignition

AbstractIn the present article, the experimental investigation of optical breakdown induced by ns/mJ pulses at two wavelengths, 1064 nm and 532 nm, in air of atmospheric pressure is reported and discussed. The obtained breakdown thresholds were compared with theory and are in good agreement. The generated plasmas have been characterized by their amount of scattered laser light, energy transmission, and change of the transmitted temporal shape. Laser-induced plasma formation in a gas, in air, also generates an acoustic pressure wave. The acoustic energy is compared to the laser pulse energy and is found to be linearly dependent. Moreover, the frequency distribution of the characteristic acoustic pressure wave was analyzed. The experiments described were accomplished in order to optimize a laser ignition system with regard to efficiency and costs. The laser system employed for these investigations is a compact high peak power, passively Q-switched, longitudinally diode-pumped solid-state laser. Such a “laser spark plug” should replace conventional spark plugs in internal combustion engines because conventional ignition has reached its limits in terms of efficiency and durability. Thereby, a reduction of pollutant emission should also be feasible.