Types and Features of Flammable Gases
Flammable Gas Sensors
Gas sensors are developed according to the characteristics of the gases to be measured. In the NDIR method, since the gas concentration is measured using the absorption of infrared rays of the target gas, it is essential to understand the infrared absorption peak wavelength that is specific to the gas.
Therefore, we will introduce here the infrared absorption spectra of inflammable gases and micro-inflammable gases and the common peaks derived from the molecular structure.
Absorption peak of infrared rays derived from the molecular structure
The molecule has an infrared absorption peak derived from its molecular structure. If it is CO2, it absorbs infrared rays in the vicinity of 4.3um as the result of bonding between C and O, and if it is NO2, it absorbs infrared rays in the vicinity of 5.3um as a result of bonding between N and O.
Many flammable gases have a bond between C and H within their molecules, absorbing gases in the vicinity of 3.4um as a result of bonding between C and H. Therefore, it is detectable by the NDIR method, and AKM offers a line-up of LED and PD products specific to this wavelength band.. We have also developed a gas sensor to detect R32 using this technique.
Typical flammable gases
Typical flammable gases include methane, propane, and ethanol. Such gases are very dangerous because they burn violently in the air or with oxygen. In fact, to ensure safety in gas fields and other areas, workers carry a portable gas sensor. It is also important to detect such gas leaks in pipelines that carry large amounts of natural gas, because even a leak of 1% amounts to a large volume.
Typical micro-flammable gases
R32 and R1234yf, which are widely used as refrigerants for air conditioning, are also known as micro-flammable gases. In the past, an incombustible refrigerant called R410 was also used. However, because of its high global warming potential (GWP), R32 and R1234yf with low environmentally friendly GWP are used. On the other hand, because these gases are micro-flammable (A2L), it is mandatory to detect leaks.
However, R32 and R1234yf are not sufficiently low in GWP. Therefore, propane, a natural refrigerant with lower GWP, is drawing attention as a future candidate. On the other hand, since propane is classified as flammable (A3), leak detection will be more critical than R32 and R1234yf.
Methane, propane, and ethanol that are listed here as flammable gases have molecular structures of CH4, C3H8, and C2H5OH respectively and R32 that is classified as micro-flammable has a CH2F2 molecular structure. You can see that any gases have a C-H bond. As an example, the absorbance spectra of methane, ethanol, and R32 are illustrated in Figure X. The infrared absorption spectra of all gases indicate that there is an absorption peak in the vicinity of 3.4um. An NDIR type gas sensor can be developed by using this absorption-wavelength band.
In addition, by using LED of AKM in an NDIR type gas sensor, it can be used at the same temperature as that of the ambient environment by shortening the emission time. This eliminates the concern for an ignition source. This makes it much safer than the semiconductor type, which heats to several hundred degrees Celsius with a heater or an NDIR type that uses lamp light source that heats to 1000 degrees Celsius or higher.
In addition, it features ultra-low power consumption and compact size, enabling the development of portable flammable gas sensor.
Figure. Infrared transmittance spectrums
Senseair, which became a member of the Asahi Kasei Microdevices (AKM) Group in 2018, is a provider of gas sensors using NDIR: Non-Dispersive InfraRed technology. Our goal is to constantly develop and mass-produce new gas sensor technologies.