Optical Combustion Pressure Sensor with Ceramic Insulation
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Solution Overview
Problem
Existing combustion pressure sensors are limited by their temperature tolerance, sensitivity to thermo-shock, and resistance to engine knock, making them unsuitable for continuous use in commercially produced internal combustion engines, as they can withstand only up to 510 °C and are prone to soot fouling and inaccurate pressure measurements due to temperature variations.
Innovation Solution
A combustion pressure sensor using optical fibre technology with a resiliently deformable membrane and two optical fibre modules, one for pressure measurement and another for temperature-induced thermal expansion correction, allowing operation between 540 °C and 750 °C, and featuring a robust connection method to withstand temperature extremes, such as soldering, brazing, or ferrule fixation, to prevent disconnection and soot regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sensor tip temperature is kept below 510°C to protect the glass bond, then the sensor body is protected from damage, but the sensor cannot prevent soot fouling which requires at least 535°C
Solution Approach 1:
The sensor is divided into two distinct temperature zones: a cooler sensor body (below 510°C) protected by ceramic insulation, and a hotter sensor tip (above 535°C) that prevents soot fouling. This segmentation allows each part to operate at its optimal temperature without compromising the other.
Solution Approach 2:
A ceramic insulating structure is introduced as an intermediary between the sensor body and the combustion chamber. This ceramic layer acts as a thermal barrier, allowing the sensor tip to be exposed to high temperatures for soot prevention while keeping the sensor body at lower temperatures for protection.
2Device complexity
If a single optical fibre is used for pressure measurement, then the device structure is simple, but temperature variations cause thermo-shock that distorts pressure measurements
Solution Approach 1:
The measurement function is segmented into two separate optical fibres: one dedicated to pressure measurement and another to temperature measurement. This allows independent measurement of each parameter without interference, eliminating thermo-shock distortion from pressure readings.
Solution Approach 2:
The second optical fibre acts as a mediator that measures temperature-induced membrane deformation separately. This temperature data can then be used to compensate for thermo-shock effects on the primary pressure measurement fibre, improving overall measurement accuracy.
3Ease of manufacture
If the optical fibre connection to the sensor body uses conventional bonding methods, then the assembly is simple, but the connection becomes damaged at temperatures above 510°C
Solution Approach 1:
The connection structure uses a composite of ceramic material and optical fibre, where the ceramic can withstand temperatures above 510°C. This composite construction maintains both the simplicity of direct connection and the durability required for high-temperature operation.
4Reliability
If a larger diameter sensor (>5mm) is used to improve reliability, then the sensor is more robust, but the sensor cannot be built into engine components like injectors or glowplugs
Solution Approach 1:
The sensor utilizes a ceramic body that provides high strength and thermal resistance, allowing for a smaller, more compact design. The ceramic material's superior mechanical properties enable the sensor to maintain robustness at a reduced diameter suitable for integration into engine components.
Solution Approach 2:
The sensor replaces traditional mechanical pressure sensing elements with an optical measurement system. This substitution allows for a more compact design while maintaining measurement capabilities, as the optical fibres and membrane structure can be miniaturized more effectively than mechanical components.
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
The solution enables continuous, accurate measurement of combustion pressure and temperature in internal combustion engines, reducing thermo-shock sensitivity and extending sensor lifespan by distinguishing between heat-induced and pressure-induced membrane deformations, thus improving engine control and efficiency.
Implementation Method 1
an end of the at least one first optical fibre module is connected to the sensor body to guide a light beam to the reflective surface and to guide the reflected light
Implementation Method 2
the at least one second optical fibre module is arranged for allowing detection of a temperature induced thermal expansion of the resiliently deformable membrane
Implementation Method 3
a resiliently deformable membrane attached to the sensor body, the membrane having a reflective surface, wherein the at least one first optical fibre is arranged for allowing measuring of a pressure induced deflection of the resiliently deformable membrane
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A combustion pressure sensor comprises a sensor body (9), at least one first optical fibre (1, 2) inserted into the sensor body (9), and a resiliently deformable membrane (7; 13) attached to the sensor body (9). The at least one first optical fibre (1, 2) is arranged for allowing measuring of a pressure induced deflection of the resiliently deformable membrane (9). An end (25) of the at least one first optical fibre (1, 2) is connected to the sensor body (9) in a manner that withstands temperatures within a range of temperatures hot enough to regenerate soot depositions on the resiliently deformable membrane (7; 13), yet cool enough to prevent melting of the resiliently deformable membrane (7; 13). When included in an internal combustion engine, at least one such combustion pressure sensor is positioned with its resiliently deformable membrane (7; 13) in direct contact with a surrounding body (8) of an engine component for direct transfer of heat to the surrounding body (8).