Vehicle Emissions & Approvals | Calibration Gases | Coregas NZ

Vehicle emissions and type approvals

New car and truck models are tested to ensure that they conform to the relevant emissions legislation. The testing equipment requires many different traceable calibration gas mixtures.

Vehicle certification

Vehicle certification is essential to obtain approval to fit an identification plate to a motor vehicle and use it on Australian roads. The Vehicle Safety Standards (VSS) branch within the Department of Infrastructure, Regional Development and Cities administers vehicle certification in Australia. State and territory registering authorities administer the subsequent use of vehicles to determine their ongoing roadworthiness and approve modifications of vehicles in service.

The certification system for new vehicles is based on 'type approval', where each vehicle model and/or type undergoes tests to demonstrate compliance with the applicable Australian Design Rules (ADRs). If the test vehicle complies, then it is deemed that all other vehicles of the same model or type will also comply. This ought to be the case if the production process is under control.

The vehicle manufacturer must ensure compliance with the ADRs. The VSS does not test vehicles for certification purposes. The vehicle manufacturer may conduct the relevant ADR tests in a location they choose. To comply with the applicable ADRs, several test vehicles may be required; this is particularly the case for passenger cars and light commercial vehicles.

Once the tests are successfully completed and approval granted, that type of car may be fitted with identification plates and used on the Australian highways and roads.

Heavy duty vehicle emissions testing

Exhaust gases from heavy vehicles are checked by state and territory authorities using instrumentation which requires specialty gas mixtures for calibration. In Australia, cars older than 5 years require a mechanical check (pink slip) before the car owner can renew their car registration. In many countries, this equivalent check would include inserting a sensor probe into the car exhaust pipe to check the emission levels of pollutant gases such as carbon monoxide and oxides of nitrogen. In Australia, however, no such emissions test is required during these 'pink slip' tests.

However, some states do conduct testing. For instance in New South Wales, the Roads & Maritime Services (the former RTA) conduct roadside spot checks on heavy vehicles, which include mechanical and emissions checks. The emissions measurement instrumentation required for these tests must be validated with calibration gas mixtures to ensure that the test has been conducted accurately.

Gas emissions limit values and instrumentation

For emissions testing, there are two relevant ADR's. ADR 79 is for light vehicles and passenger cars. In Table 1 of section of the ADR 79/04 the emissions limits values are presented for gaseous emissions of carbon monoxide, total hydrocarbons (THCs), combined nitrogen oxides (NOx) and non-methane hydrocarbons (NMHCs). The limit values are expressed in mg/km to regulate the impact of the vehicle over its use. There is no generic way to convert these values to a ppm measurement; this can only be done with a detailed understanding of the vehicle.

ADR 79 also specifies the type of instrumentation that must be used to conduct the testing. In line with vehicle emissions testing around the world, Annexe 4a, Appendix 3, section 1.3 refers to the following: CO and CO2 analysis using non-dispersive infra-red (NDIR); methane and THC analysis using flame ionisation detection (FID); and NOX with either chemiluminescence or non-dispersive ultra-violet resonance absorption (NDUVR).

ADR 80 is relevant for heavy duty vehicles. ADR 80/03 refers to Directive 2005/55/EC. Within that directive, there are gaseous emissions limit values for carbon monoxide, hydrocarbons and combined oxides of nitrogen (NOx). The limits are expressed in g/kWh of power generated and, similar to the limits in ADR 79, conversion of these to a ppm measurement value can only be done with a full understanding of the engine power performance characteristics.

Both ADRs also refer to particulate emissions (PM). However, PM emissions are measured using different types of instrumentation and calibration techniques to the gaseous chemical species emissions, which require specialty gases calibration mixtures to validate the testing.

Instrumentation calibration and verification

Section 2.1 of ADR 79/04 explains the calibration requirements for the analytical instrumentation: they must be calibrated in the month of any 'type testing' and once every six months for ongoing production quality control validation. In addition, a recalibration must take place if a verification test result is outside the acceptable range.

According to section 2.2 of ADR 79/04, verification tests must be conducted prior to and after each emission test measurement. The validation requires the use of a zero gas and a span gas which must have a nominal value within 80 to 95% of the target measurement concentration. A gas diluter may be used to achieve this concentration, so a single cylinder of calibration gas mixture can be used to cover a variety of tests and verification points.

The rules for calibration are set out in section 2.1 of the ADR 79/04. An important point to note is that the concentration of the calibration gas must be at least 80% of the full scale deflection of the instrument. As with the verification process, a gas diluter may be used as long as the accuracy it can produce the diluted gas mixture to an accuracy of plus or minus 2%.

Pure gases and instrumentation gas mixtures

According to section 3.1 of the ADR 79/04, the following pure gas ans instrumentation gas mixture specifications are relevant for instrument calibration and operation:

  • Purified nitrogen: (purity: ≤1 ppm C, ≤1 ppm CO, ≤400 ppm CO2, ≤0.1 ppm NO)
  • Purified synthetic air: (purity: ≤ 1 ppm C, ≤1 ppm CO, ≤400 ppm CO2, ≤0.1 ppm NO); oxygen content between 18 and 21% volume
  • Purified oxygen: (purity: > 99.5% volume O2)
  • Purified hydrogen: (and a mixture containing 40% hydrogen in helium): (purity ≤1 ppm C, ≤400 ppm CO2)
  • Carbon monoxide: (minimum purity 99.5%)
  • Propane: (minimum purity 99.5%)

All of these instrumentation gases are available at concentrations suitable for vehicle type testing from Coregas.

Calibration gas mixtures

According to section 3.1 of the ADR 79/04, calibration gas mixtures with a true concentration value within plus or minus 2% of the stated figure for the following chemical compositions shall be available:

  • C3 H8 in a balance of purified synthetic air
  • CO in a balance of purified nitrogen
  • CO2 in a balance of purified nitrogen
  • NO in a balance of purified nitrogen (the amount of NO2 contained in this calibration gas shall not exceed 5% of the NO content)

All of the above calibration gases are available from Coregas at concentrations suitable for vehicle type testing.


Gas delivery equipment

In addition to the calibration gas mixtures, high purity gases and instrumentation gas mixtures it is essential to use high quality gas delivery equipment and piping to deliver the gases from the gas store to the instrumentation. At Coregas, we have a comprehensive range of Spectrolab equipment which is ideal for the specialty gases required for vehicle emissions testing. Here are some product guidance notes:

For intermittent use calibration gas mixtures: either a single stage regulator mounted on the cylinder or a single stage wall mounted gas supply panel. This is the lowest cost option for gas supply.

For frequent use calibration gas mixtures and zero gases: a single stage automatic change over unit. The advantage over the simple regulator / panel is that the system will switch from an empty gas cylinder to a full one without interruption to the gas supply. This makes the test process seamless and minimises operator change overs and therefore maximises productivity.

For continuous use instrumentation gases such as synthetic air and 40% Hydrogen in Helium FID Fuel gas mixture: a two stage automatic change over unit. The advantage over the single stage automatic change over unit is that the delivery pressure of the gases is held stable over the lifetime of the gas cylinder. This ensures a steady flow of these gases to the FID flame.

Gas delivery system design and installation

Our technical services team at Coregas have had years of experience in the design and installation of high purity and calibration gas mixture supply systems. They can advise you on the most suitable gas control equipment and piping options and would then be ready to procure the relevant materials and complete the installation in your vehicle emissions testing laboratory: the "full service" option.