Laser Ignition Optical Window Pseudo Mirror Management
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Solution Overview
Problem
Laser ignition apparatuses for difficult-to-ignite engines, such as highly-charged, high-compression, and natural gas engines with large bore cylinders, face issues with contamination on the combustion chamber-side end surface leading to pseudo mirror formation, which causes damage to focusing lenses and protective covers due to reflected laser light, resulting in reduced power density and unreliable ignition.
Innovation Solution
The apparatus includes an excitation light source, regulating optical element, laser resonator, enlarging optical element, focusing optical element, and an optical window member, where the catoptric-light focal point is positioned in a region with no solid material, preventing damage and maintaining high power density by ensuring the power density of the pulsed laser light is above the burn-off threshold for contaminants and below the damage threshold for optical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser light with high power density is irradiated to burn off contaminants on the combustion chamber-side end surface, then the contaminants are removed and the surface is cleaned, but a pseudo mirror is formed by the fouled protective cover, causing reflection and formation of a catoptric-light focal point that concentrates energy and damages the focusing lens or protective cover
Solution Approach 1:
An optical window member is introduced as an intermediary component between the combustion chamber and the focusing lens. This window member is specifically designed to withstand high temperatures and is positioned to allow the catoptric-light focal point to form in the space between the window member and the focusing lens, rather than directly on the focusing lens or protective cover, thereby preventing damage to critical optical components
Solution Approach 2:
The invention accepts that a pseudo mirror will form on the optical window member and converts this harmful reflection into a beneficial arrangement by positioning the catoptric-light focal point in a safe location (in the space between the window member and focusing lens) where it cannot cause damage. The reflected energy is thus redirected to a harmless location while the primary laser beam continues to function for ignition
2Power
If the catoptric-light focal point is positioned within the focusing lens or protective cover, then the reflected laser light is focused at that point, but concentration of energy generates plasma or shock waves that cause damage such as cracks or peeling of AR coating
Solution Approach 1:
The optical window member serves as a mediator that separates the source of reflected energy (pseudo mirror on window member) from the vulnerable components (focusing lens and protective cover). By positioning the catoptric-light focal point in the space between the window member and focusing lens, the invention ensures that the concentrated energy does not directly impact the structural integrity of critical optical components
Solution Approach 2:
The invention changes the spatial dimension of the problem by moving the catoptric-light focal point from a position within or on the protective cover/focusing lens to a position in the space between the optical window member and the focusing lens. This dimensional relocation prevents energy concentration on vulnerable surfaces while maintaining the ignitive function at the primary focal point in the combustion chamber
3Ease of manufacture
If the focusing lens or protective cover is damaged, then scattering of laser light occurs, but the power density at the focal point is lowered, making it difficult to reliably ignite the air-fuel mixture
Solution Approach 1:
The optical window member acts as a protective intermediary that absorbs the harmful effects of catoptric light reflection. By positioning the catoptric-light focal point in the space between the window member and focusing lens, the invention protects the focusing lens and protective cover from damage, thereby preventing light scattering and maintaining high power density at the focal point for reliable ignition
Solution Approach 2:
The optical window member provides beforehand cushioning protection against the harmful effects of pseudo mirror formation. By designing the system to anticipate and accommodate the formation of a pseudo mirror on the window member, the invention prevents this reflected energy from damaging the focusing lens or protective cover, thereby maintaining system reliability and preventing degradation of ignition performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration ensures stable ignition by preventing damage to the focusing optical element and optical window member, maintaining high power density at the focal point, and reliably igniting the air-fuel mixture while keeping the combustion chamber-side end surface clean.
Implementation Method 1
irradiate an excitation light generated by an excitation light source (e.g., a flash lamp or a semiconductor laser) to a laser resonator (or optical resonator) that includes a laser medium and a Q switch, thereby causing the resonator to generate a pulsed laser light
Implementation Method 2
The enlarging optical element is configured to enlarge the beam diameter of the pulsed laser light outputted from the laser resonator
Implementation Method 3
The focusing optical element is configured to focus the beam diameter-enlarged pulsed laser light outputted from the enlarging optical element to a predetermined focal point in a combustion chamber of an engine, thereby igniting an air-fuel mixture in the combustion chamber
Implementation Method 4
a catoptric light resulting from the reflection of the laser light by the pseudo mirror is focused
Data Source
AI summary
In a laser ignition apparatus, a focusing optical element is configured to focus a pulsed laser light to a predetermined focal point in a combustion chamber of an engine. An optical window member is arranged on the combustion chamber side of the focusing optical element so as to separate the focusing optical element from the combustion chamber. A catoptric-light focal point, at which a catoptric light is to be focused, is positioned on the anti-combustion chamber side of a combustion chamber-side end surface of the optical window member. The catoptric light results from the reflection of the pulsed laser light by a pseudo mirror that is formed by the optical window member when the combustion chamber-side end surface thereof is fouled with contaminants. Further, the catoptric-light focal point falls in a region where no solid material forming either the focusing optical element or the optical window member exists.