Optical diagnostics on the pre-chamber jet and main chamber ignition in the active pre-chamber combustion (PCC)

Laser ignition (LI) allows for precise manipulation of ignition timing and location and is promising for green combustion of automobile and rocket engines and aero-turbines under lean-fuel conditions with improved emission efficiency; however, achieving completely effective and reliable ignition is still a challenge. Here, we report the realization of igniting a lean methane/air mixture with a 100% success rate by an ultrashort femtosecond laser, which has long been regarded as an unsuitable fuel ignition source. We demonstrate that the minimum ignition energy can decrease to the sub-mJ level depending on the laser filamentation formation, and reveal that the resultant early OH radical yield significantly increases as the laser energy reaches the ignition threshold, showing a clear boundary for misfire and fire cases. Potential mechanisms for robust ultrashort LI are the filamentation-induced heating effect followed by exothermal chemical reactions, in combination with the line ignition effect along the filament. Our results pave the way toward robust and efficient ignition of lean-fuel engines by ultrashort-pulsed lasers.

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Robust and ultralow-energy-threshold ignition of a lean mixture by an ultrashort-pulsed laser in the filamentation regime

Visualization study on lean combustion characteristics of the premixed methanol by the jet ignition of an ignition chamber

Utilizing drones in many applications such as video and photography, farms, search and rescue operations, construction industry for mapping and site monitoring has increased. However, their operating time is limited according to the capacity of their batteries. Therefore, many researchers attempt to enhance the operating time of drones. In this study, to the best of the authors' knowledge for the first time, the feasibility assessment of a laser-based wireless power transfer (WPT) mechanism is theoretically investigated on drone applications to increase their operating time. In this method, drones can be charged during operation wirelessly at a considerable distance with acceptable efficiency. The Analytical code is developed in Engineering Equation Solver (EES) software. The acquired results for the main components of the system have a good agreement with published papers of other researchers. In this study, three commercial photovoltaic (PV) materials were evaluated. The results show that an equipped drone with laser-based WPT system is able to approximately receive net power of 73.5, 62.6, and 33.2 W at a 500 m distance by GaAs, CdTe, and c-Si PV materials, respectively, while the laser module consumes around 600 W electrical power. Moreover, since the optical power of the laser is concentrated on PV panel, a two-phase cooling system is suggested for PV panel to reduce the temperature of the under radiate area. Results demonstrate that the temperature of GaAs PV material without a two-phase cooling system is approximately three times more than the temperature of PV panels with a two-phase cooling system at high power transfer rates.

Feasibility assessment of next-generation drones powering by laser-based wireless power transfer

The stringent emission norms, increasing demands for higher efficient and reliable engine operation and rapid depletion of petroleum resources, motivated researchers to explore on advanced combustion and ignition technologies as well as the use of alternative fuels for internal combustion (IC) engines. Lean burn combustion with high spark energy is an advanced combustion approach that improves thermal efficiency, reduces knocking tendency, exhaust emissions, especially NOx (Nitrogen oxides), and heat transfer. However, there are many difficulties in current operating engines with lean mixtures like slower flame initiation, incomplete combustion, increased cyclic variation and potential misfiring, etc. which causes decreased efficiency, power output, and excessive emission. The exhaust gas recirculation (EGR) can reduce nitrogen oxide (NOx) emissions but increases particulate matter (PM) and have ignition problem during engine idle operation. The conventional electric discharge ignition system performs well at normal operating conditions; however, for igniting lean mixtures require significantly higher spark energy with multi-point ignitions. The higher spark energy will increase the ignitibility but decrease the life of spark plug due to electrode erosion, and electrodes act as a thermal energy sink. However, multi-location ignitions with conventional electric discharge systems will require several electrodes. Therefore to overcome these difficulties, the multi-point laser-induced ignition is an innovative alternative approach to burn lean mixtures compared to the conventional electric discharge ignition system. A laser is a high energy electrode less ignition source with the easy possibility of multi-location ignitions. Therefore, this article aims is to review various techniques used for multi-point laser ignition and its impact on combustion characteristics and engine performance. The effect of laser energy and ignition locations on combustion characteristics has also been reviewed. Also, demonstration and realization of the laser spark plug with multiple beam output, which can be used as multi-point igniters in internal combustion engines has been reviewed.

Review: Multipoint laser ignition system and its applications to IC engines

Lean-burn combustion using higher spark energy can enhance the combustion characteristics and emission performance. A laser is electrodeless with a high energy ignition source and can achieve multi...

Numerical simulation of combustion characteristics and emission predictions of methane-air and hydrogen-air mixtures in a constant volume combustion chamber using multi-point laser-induced spark ignition

CFD Simulation of Gaseous Fuel Combustion in Constant Volume Combustion Chamber using Multi-Point Laser Ignition

The laser-induced spark ignition (LISI) of methane (CH4)-air mixtures were experimentally studied in a constant volume chamber. The experiments were carried with a nanosecond pulsed Nd: YAG laser of 1064 nm wavelength. A piezoelectric pressure transducer coupled to a DAQ system was used for measurement of pressure–time history. The chamber has four diametrically opposite optical windows; two optical windows for laser beam entry and exit and two for optical diagnostics. The experiments were carried out at an initial chamber pressure of 2.5, 5.0, and 7.5 bar and at chamber temperature of 298 K. The minimum pulse energy and breakdown threshold intensity required for breakdown of both pure air and methane goes on decreasing as the initial chamber pressure goes on increasing from 1.0 to 8.0 bar. The pressure–time (p–t) history was recorded for different equivalence ratios (0.6 to 1.4) and at different initial chamber pressure conditions. The peak pressure was observed at ϕ = 1.0 for all initial chamber pressure conditions and as chamber pressure increases from 2.5 to 7.5 bar the peak pressure rises and time to attain peak pressure reduces. The minimum pulse energy needed for burning of methane-air mixture was observed at ϕ = 1.0 and it reduces as chamber pressure increases from 2.5 to 7.5 bar. The analyzed data will be useful to study the behavior of laser ignition of the methane-air mixture and can be useful to develop commercial LISI engines in future. 

Prashant Mahadev Patane

Papers

Review: Multipoint laser ignition system and its applications to IC engines

Numerical simulation of combustion characteristics and emission predictions of methane-air and hydrogen-air mixtures in a constant volume combustion chamber using multi-point laser-induced spark ignition

CFD Simulation of Gaseous Fuel Combustion in Constant Volume Combustion Chamber using Multi-Point Laser Ignition

Laser-Induced Spark Ignition of Methane-Air Mixtures in Constant Volume Combustion Chamber