Emission testing is a crucial aspect of vehicle regulation, ensuring that automobiles meet environmental standards. For benzine (gasoline) cars, understanding the intricacies of emission testing procedures, especially concerning On-Board Diagnostics (OBD2) and related systems like CAS (Calibration Application System), is vital for both car manufacturers and repair experts. This article delves into the emission testing landscape, focusing on benzine vehicles and the role of OBD2 in maintaining compliance.
Emission Test Procedures for Benzine Vehicles
Modern emission testing for benzine cars is conducted using chassis dynamometers to simulate real-world driving conditions in a controlled laboratory environment. These tests are designed to measure pollutants in grams per kilometer (g/km), except for Particle Number (PN), which is measured in particles per kilometer (1/km). Over the years, the regulatory landscape has evolved with changes in test cycles, reflecting a growing understanding of vehicle emissions.
Initially, the New European Driving Cycle (NEDC) was the standard. However, to better represent real-world driving, the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) was introduced. During the transition, a correlation tool (CO2MPAS) bridged the gap between NEDC-based CO2 targets and the new WLTP standards. By 2020, NEDC-based CO2 targets were converted to WLTP targets to maintain comparable stringency.
The implementation of Euro 5 and Euro 6 standards brought significant advancements in emission measurement methodologies, particularly for Particulate Matter (PM) and Particle Number (PN). These new methods, developed by the UN/ECE Particulate Measurement Programme (PMP), are more rigorous. The PM mass measurement method is now akin to the US 2007 procedure. While regulatory PM mass emission limits were adjusted to reflect the change in measurement methods, PN emissions in benzine and diesel cars are measured over the NEDC/WLTC test cycle using the PMP particle number method, as detailed in UN/ECE Regulation 83 Suppl. 7.
For the upcoming Euro 7 standards, the exhaust emission test procedures are expected to remain largely consistent with Euro 6. For passenger cars (M1) and light commercial vehicles (N1) powered by benzine engines, the following regulations are key:
- Laboratory Exhaust Emissions: UN Regulation No 154 (UN Regulation No 154—Uniform provisions concerning the approval of light duty passenger and commercial vehicles with regards to criteria emissions, emissions of carbon dioxide and fuel consumption and/or the measurement of electric energy consumption and electric range (WLTP), 02 series of amendments) is the governing standard. This ensures that benzine vehicles are tested under standardized conditions to measure exhaust pollutants.
- Real Driving Emissions (RDE): UN Regulation 168 (UN Regulation No 168, Original version) is applied for RDE testing. This is crucial for benzine cars to ensure that low emissions are maintained not only in the lab but also on real roads.
- Evaporative Emissions: UN Regulation No 154, Level 1A (4-phase WLTP) (02 series of amendments) dictates the evaporative emissions testing, important for controlling hydrocarbon emissions from benzine fuel systems.
- Brake and Tire Emissions: While primarily focused on exhaust emissions, regulations are expanding to include other sources. Brake particle emissions for M1 and N1 vehicles are tested according to UN Global Technical Regulation No 24. Furthermore, tire abrasion limits for C1 tires will be based on methodologies developed in UN WP.29, although these are less directly related to benzine engine operation itself but are part of broader vehicle environmental impact.
Real Driving Emissions (RDE) Testing for Benzine Engines
Since the Euro 6d-TEMP stage, Real Driving Emissions (RDE) testing has become mandatory, supplementing laboratory tests. This is particularly relevant for benzine cars as it ensures emission control systems perform effectively under diverse, real-world driving conditions. RDE tests employ Portable Emissions Monitoring Systems (PEMS) mounted on the vehicle during operation.
An RDE test for a benzine vehicle typically lasts between 90 and 120 minutes and must include a mix of driving environments: urban, rural, and motorway, each constituting roughly one-third of the test duration and covering at least 16 km. The speed limits for these segments are defined to reflect typical driving patterns (urban: up to 60 km/h, rural: up to 90 km/h, motorway: up to 145 km/h).
For benzine vehicles under Euro 6 standards, it’s mandatory to measure and record NOx, CO, and PN emissions during RDE tests. The on-road emission limits are determined by multiplying the laboratory emission limit by a conformity factor (CF). This factor acknowledges the variability between lab and real-world conditions.
The Role of OBD2 and CAS in Emission Control and Testing
On-Board Diagnostics II (OBD2) systems are integral to modern benzine cars. They continuously monitor the performance of the engine and emission control systems. A key aspect related to emission testing is the Calibration Application System (CAS), which is often intertwined with the OBD2 system’s functionality. CAS is used during vehicle development and testing to calibrate engine control parameters to optimize performance and minimize emissions. In the context of OBD2, CAS data and calibration settings are crucial for ensuring the emission control system operates as intended throughout the vehicle’s life.
The OBD2 system in a benzine car monitors various sensors and actuators related to emission control, such as oxygen sensors, catalytic converter efficiency, fuel trim, and more. When an emission-related fault is detected, the OBD2 system stores Diagnostic Trouble Codes (DTCs) and typically illuminates the Malfunction Indicator Lamp (MIL) on the dashboard. These DTCs provide valuable information for repair technicians to diagnose and rectify emission issues.
During emission testing, especially periodic technical inspections, the OBD2 system is interrogated. A key part of the test is to check for stored DTCs and ensure the MIL is not illuminated, indicating that the emission control system is functioning correctly according to the manufacturer’s calibration (often managed through CAS). Furthermore, some advanced emission tests might involve reading live data from the OBD2 system to verify sensor readings and system parameters in real-time.
Defeat Devices and the OBD2 System
Regulatory scrutiny on “defeat devices” is significant in emission control. EU regulations define a defeat device as:
any element of design which senses temperature, vehicle speed, engine speed (RPM), transmission gear, manifold vacuum or any other parameter for the purpose of activating, modulating, delaying or deactivating the operation of any part of the emission control system, that reduces the effectiveness of the emission control system under conditions which may reasonably be expected to be encountered in normal vehicle operation and use.
The regulations prohibit defeat devices, but exceptions exist, primarily to protect the engine or enable cold starting. However, the definition of “emission control system” itself is critical. In the context of OBD systems, it’s defined as:
the electronic engine management controller and any emission-related component in the exhaust or evaporative system which supplies an input to or receives an output from this controller.
This OBD-centric definition is notable as it doesn’t explicitly include fuel system parameters, combustion system design, or the Exhaust Gas Recirculation (EGR) system, even though these are crucial for emission control in benzine engines.
The OBD2 system plays a vital role in preventing and detecting defeat devices. By continuously monitoring the performance of emission-related components, OBD2 is designed to identify malfunctions or manipulations that could lead to increased emissions. Manufacturers must demonstrate that their emission control strategies are not defeat devices and that the OBD2 system is effective in monitoring and reporting emission-related faults under normal operating conditions.
While EU regulations outline the prohibition of defeat devices, the process for manufacturers to apply for exemptions remains somewhat ambiguous. Transparency and clear guidelines are essential to ensure fair compliance and effective enforcement against emission cheating.
Conclusion
Emission testing for benzine cars is a complex and evolving field, driven by the need for cleaner air and stricter environmental regulations. Understanding the test procedures, the significance of Real Driving Emissions, and the critical role of OBD2 systems and CAS is paramount. For car repair experts, proficiency in diagnosing emission-related issues using OBD2 tools and understanding the calibration data linked to CAS is increasingly important. As emission standards like Euro 7 approach, the focus on robust testing and effective OBD2 monitoring will only intensify, ensuring benzine vehicles contribute to a more sustainable future.
