An instrument called an exhaust gas analyzer is used to measure combustion-related exhaust gases. It successfully monitors the various gases present and provides measurements regarding their contents. It is also known as a portable emission analyzer. Some gas analyzers can also identify the potential fire starters if fuel is accidentally discharged. Even engine efficiency can be determined by some other models. Automotive exhaust gas analyzers are multi-gas analyzers that can detect carbon monoxide (CO), carbon dioxide (CO2), fuel-dependent hydrocarbons (HC), oxygen, and HC infrared (NDIR) (O2). Gas analyzers analyse exhaust gases using NDIR and chemical sensors.
Automotive Exhaust Gas Analyzers are typically employed to identify and resolve issues with engine emissions and to enhance engine performance. Gas analyzers assist with emission compliance and immediately give precise and reliable results. They are used to calculate the levels of gases such as carbon monoxide. Real-time combustion efficiency is calculated utilising gas measurements using both chemical and infrared gas analyzers. Checking the operation of the evaporative emission system, no-start situations, exhaust system leaks, evaporative emission system leaks, gasoline smells inside the car, etc. are some more uses.
Operation of the emission analyser
The emission analyzer functions in a manner similar to that of the heavy emission testing machine. Through the keypad, the information about the test vehicle is entered. These specifics include the test date, the licence plate number, the engine type, and the year and model of the vehicle. The reference circuit is then used to monitor the engine's oil temperature and revolutions per minute (RPM). Both diesel and gasoline engines' oil temperatures must be at least 70 degrees Celsius, and before the measurement may start, the engine's revolutions per minute (RPM) must reach 3500 for diesel engines and 2500 for gasoline-powered cars.
The opacimeter will be the one to provide information to the microcontroller if the car is diesel-fueled. If it is gasoline, the microcontroller will get data from the gas sensors. The data is read by the microcontroller's analog-to-digital converter and sent to the LCD display and thermal printer.
Components of Exhaust Emission Analyser
1) Keypad and LCD
There are 12 buttons on the keypad, and the LCD contains 4 lines with 20 characters. Through RS232, the keypad is connected to the microcontroller. The keys have been configured to represent letters or numbers. The character that is transmitted to the LCD through the microcontroller is determined by how many times the Enter key is pressed after that.
2) Reference Circuit
It has a spinning element, an oscillator, an SCR, a power inverter, and a xenon flash light. A reference line identifies the spinning piece. The rotor will revolve exactly once for each flash of light if the light flashes at the same rate that the motor rotates. The rotor will look motionless to an observer.
For engines fueled by gasoline, the stroboscope is calibrated to determine the corresponding frequency that must be produced by the oscillator when it is set at 2500 RPM and 3500 RPM (for diesel powered engines). The frequencies are discovered to be respectively 41.67 Hz and 58.33 Hz.
3) Opacimeter
The quantity of light that is blocked out by atmospheric pollution is known as opacity. A light source and an LDR may be used to measure opacity, with the resistance of the LDR being a function of the amount of light it receives when a gas and particle combination travels between the light source and the LDR. The sample of smoke emission is fed via a chamber with the shape of a funnel made of aluminium sheet. The blackness or opacity of the smoke is determined by the quantity of light that penetrates through.
4) Gas Sensors
The three gases that are often released by gasoline-powered cars are measured using two gas sensors. The CO and HC detection ranges for the Iridium 50 gas sensor are 0-15% for Carbon Monoxide and 0-10000 ppm for Hydrocarbons. Nitrous Oxide may be detected by the NOXO100 gas sensor up to 5000 ppm. The IRidium 50 gas sensor is connected to circuits that enable RS232 serial connections for direct contact with the microcontroller.
5) Microcontroller
The microcontroller contains a 10-bit ADC, two full-duplex UARTs, 64K flash memory, 4K RAM, and a number of I/O ports. Z8! Encore is written in the C programming language. When the initialization signal from the reference circuit is received by the microcontroller, an algorithm is created to tell it to start collecting data from the sensors attached to the UARTs and ADC.
6) Thermal Printer
The Epson TM-T88 thermal printer is connected to the Zilog microcontroller's UART. The printout includes the test date, the plate number, and the quantity of gases that were found.
Techniques used for analysing Exhaust emission
Methods like Non-Dispersive Infra-Red, Flame Ionization Detector, Chemiluminescence Analyzer, Fourier Transform Infra-Red, Laser Diode Spectrometer, Magnetic Methods are some of the most popular methods for analysing Exhaust emission. These methods are all based on a certain physical characteristic of the gas being measured. Even when the measured species is subjected to a chemical reaction in the analyzer, only an ancillary physical attribute is directly assessed.
The above analytical methods have been created or implemented in order to measure internal combustion engine exhaust gases. They provide a respectable level of precision and are impervious to cross-species interference. These techniques are frequently employed for compliance checks and emission certification.
Working of the of the techniques explained
Analyzers used for certification and compliance testing are not ideal for real transient engine testing due to their sluggish reaction times. In order to be precise, sensitive, and stable, steady-state analyzers often have lengthy reaction times and are adequately dampened. Transient work requires extremely rapid analysis, ideally within a few milliseconds. An additional issue in transient testing is caused by the location of the exhaust gas sample stations, which are downstream of the engine, and the accompanying time and distance delays. Reconstructing the genuine signal from the instrument signal using mathematical methods that account for sampling delays and instrument response characteristics.
