Blog – Simulating Drive Cycles to Optimise Catalyst and Aftertreatment System Design.

By Dr Kurtis Irwin, VP Global Catalysis, CATAGEN

A drive cycle is a set of operating conditions that a vehicle must go through to measure its emission and fuel economy performance. The cycle consists of a specific sequence of accelerations, decelerations, and constant speed driving, which is designed to simulate typical driving patterns.

Drive cycles are used to test and certify vehicles for compliance with emissions and fuel economy standards set by regulatory agencies, such as the Environmental Protection Agency (EPA) in the United States or the European Commission in Europe.

Catalysts are designed to convert harmful exhaust gases, such as carbon monoxide, nitrogen oxides, and hydrocarbons, into less harmful emissions, such as carbon dioxide, water, and nitrogen. The performance of the catalyst depends on the temperature and composition of the exhaust gases, which vary depending on the driving conditions. Therefore, catalysts are designed to operate most effectively within a specific temperature range, which can be affected by the driving cycle.

To ensure that catalyst and aftertreatment systems are effective under a wide range of driving conditions, they must be tested using a variety of drive cycles. By subjecting vehicles to different types of drive cycles, engineers can evaluate the performance of the catalyst and aftertreatment systems in a variety of conditions and adjust their design as needed to improve their effectiveness.

The Worldwide Harmonized Light Vehicles Test Cycle (WLTC) is a drive cycle used to measure the emissions and fuel economy of light-duty vehicles worldwide. The WLTC was developed to replace the previous New European Driving Cycle (NEDC), which was criticized for not accurately reflecting real-world driving conditions. 

The WLTC consists of four phases, each with a different speed and acceleration profile, and it includes both urban and suburban driving conditions. The drive cycle is designed to be more representative of real-world driving conditions and is intended to provide more accurate measurements of emissions and fuel economy. 

The emissions limits for the WLTC vary depending on the type of vehicle and its engine size. For gasoline-powered vehicles, the WLTC emissions limits for carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM) are:

• CO: 1.0 g/km 
• NOx: 0.06 g/km 
• PM: 0.0045 g/km (for direct injection engines) or 0.025 g/km (for non-direct injection engines) 

For diesel-powered vehicles, the WLTC emissions limits for CO, NOx, and PM are: 

• CO: 1.0 g/km 
• NOx: 0.08 g/km 
• PM: 0.0045 g/km 

It’s important to note that these limits are intended to be more stringent than the previous NEDC emissions limits, and they are expected to be updated periodically as emissions standards evolve. 

Along with the WLTC, there has also been a specific motorcycle drive cycle developed; The Worldwide Motorcycle Test Cycle (WMTC) is a standardized test procedure used to measure the emissions and fuel economy of motorcycles and scooters worldwide. The WMTC was developed by the United Nations Economic Commission for Europe (UNECE) and is used as the basis for emissions regulations in many countries around the world. 

The WMTC consists of two parts: a low-power test (LPT) and a high-power test (HPT). The LPT is designed to simulate urban driving conditions, while the HPT is designed to simulate highway driving conditions. Each part of the test consists of four different speed and acceleration phases, and the entire test lasts approximately 20 minutes. 

During the test, the motorcycle or scooter is placed on a chassis dynamometer, which simulates the resistance of the road. The vehicle is then driven through the different phases of the test, and its emissions and fuel economy are measured. 

The emissions limits for the WMTC vary depending on the type of motorcycle or scooter and its engine size. The limits for carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) are set based on the vehicle’s engine displacement and power output. For example, for motorcycles with an engine displacement of less than or equal to 50 cc, the WMTC emissions limits are: 

• CO: 4.5 g/km 
• HC: 0.8 g/km 
• NOx: 0.12 g/km 

For motorcycles with larger engine sizes, the emissions limits are generally more stringent. 

Overall, the WMTC provides a standardized method for measuring the emissions and fuel economy of motorcycles and scooters, and it is used to set emissions regulations in many countries around the world. 

CATAGEN have developed the ability to conduct this testing in an OMEGA reactor without the need for an engine, motorcycle or rolling road. The OMEGA reactor can accurately recreate the catalyst inlet conditions for temperature, flow rates and gas concentrations. This allows for testing and development of the catalysts and aftertreatment systems much earlier in the development phase and also understand the tailpipe emissions much earlier in the development process. 

CATAGEN’s Omega Technology can be used to recreate a wide range of drive cycles, including those developed by regulatory agencies such as the EPA. By simulating a drive cycle on the aftertreatment systems, engineers can evaluate how a vehicle’s emissions will be affected by different driving conditions and can optimize the aftertreatments design and performance accordingly. 

In addition to simulating drive cycles, CATAGEN can also be used to optimize catalyst and aftertreatment system design. The OMEGA reactor can be used to test different types of catalysts and aftertreatment systems and understand how they will perform under different driving conditions, allowing engineers to select the most effective system for a given vehicle and drive cycle. 

Overall, CATAGEN can help streamline the drive cycle testing process and improve the accuracy and efficiency of development of the aftertreatment systems and emissions testing. 

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