Emission Control Systems

Understanding Emission Control Systems: Types and How They Work

Introduction:

Do you recall the time when the nation experienced a three-month lockdown? During that period, the air quality improved significantly, and the environment became cleaner due to reduced emissions. One of the key sources of harmful emissions is our vehicles, and to combat this issue, engineers have developed emission control systems. In this article, we will explore what an emission control system is, how it functions, and delve into the different types of emission control methods in use today.

What is an Emission Control System?

An emission control system is a series of functions implemented by vehicles to minimize harmful emissions such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). These systems are classified into two main categories: prevention or active systems and destruction or passive systems. While advancements in automotive engine technologies have led to some reduction in emissions, more impactful methods are required to meet stringent emission standards.

Catalytic Converters: Reducing Tailpipe Emissions

Catalytic converters are essential components found in all vehicles, designed to destruct tailpipe emissions. Over the years, catalytic converters have evolved, with modern three-way catalytic converters effectively controlling CO, HC, and NOx emissions. These converters transform harmful gases into carbon dioxide (CO2) and water (H2O). They contain precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) that facilitate oxidation to convert pollutants into less harmful compounds.

To maintain optimal efficiency, catalytic converters require heat. However, during cold starts, their efficiency can be reduced. To address this, many car manufacturers now utilize secondary batteries to pre-heat the catalytic converter as soon as the vehicle is started. Overall, catalytic converters play a pivotal role in destructing harmful emissions.

Evaporative Emission Control: Saving Fuel and Reducing Emissions

The evaporative emission control system not only reduces emissions but also enhances fuel efficiency. It prevents the evaporation of hydrocarbons from the fuel tank by collecting and circulating them into the combustion chamber. The system relies on a carbon canister, which absorbs fuel vapors through loose chemical bonds. When necessary, these vapors are released via a purge solenoid, controlled by the vehicle's onboard computer module.

The collected fuel vapors are then channeled into the engine's intake manifold through the Positive Crankcase Ventilation (PCV) valve and undergo combustion. This process saves fuel and prevents the escape of vapors through the fuel tank lid during refueling, thus contributing to emissions control.

Exhaust Gas Recirculation (EGR): Lowering Emissions and Engine Temperatures

Exhaust Gas Recirculation (EGR) is a beneficial system that lowers emissions and helps maintain lower engine temperatures. Commonly found in turbocharged petrol and diesel engines, EGR channels a portion of the exhaust gases back into the intake manifold. In petrol engines, EGR is used to increase efficiency, while in diesel engines, it primarily reduces NOx emissions.

The exhaust gases being recirculated are already burnt and inert, which means they decrease the combustion capacity in each cylinder, leading to lower heat production and subsequently lower emissions. However, it's essential to note that EGR slightly reduces engine power and is inactive until the engine reaches its optimum operating temperature.

Diesel Particulate Filter (DPF): Trapping and Burning Soot

The Diesel Particulate Filter (DPF) is a honeycomb filter designed to trap soot produced during combustion in the exhaust manifold. Over time, the collected soot is burnt through a process called regeneration, which occurs while driving at specific engine RPMs in a controlled environment.

Car manufacturers recommend following a regeneration cycle to maintain the DPF's health and efficiency. Adequate exhaust temperature and a sufficient level of oxygen are necessary for smooth regeneration. Modern vehicles inform the driver about the DPF's clogging activity, ensuring the process is carried out seamlessly.

Selective Catalyst Reduction (SCR): Reducing NOx Emissions in Diesel Engines

Selective Catalyst Reduction (SCR) is an advanced emission control method predominantly used in high-capacity diesel engines to meet stringent emissions standards like BS6. SCR involves injecting a liquid urea known as Diesel Exhaust Fluid (DEF) or AdBlue into the exhaust system. The fluid reacts with NOx emissions, converting them into less harmful nitrogen, water, and CO2, which are then expelled from the exhaust pipe.

SCR systems can significantly reduce NOx emissions, helping vehicles comply with strict emissions regulations.

Frequently Asked Questions (FAQ):

Q1: Does the catalytic converter affect emissions?

Ans: Yes, the catalytic converter plays a crucial role in reducing emissions. It acts as the main emission control unit in a vehicle, trapping harmful gases and converting them into less harmful substances like nitrogen, water, and carbon dioxide. Without a catalytic converter, vehicles would emit significantly higher levels of pollutants, posing a threat to the environment.

Q2: How does the emission control system work?

Ans: The emission control system operates in coordination with various other systems in a vehicle. It can be broadly categorized into two types: preventive and destructive methods. The primary objective is to minimize emissions while ensuring the vehicle's efficiency and performance are not compromised.

Q3: What are the common faults with the emission control system?

Ans: The emission control system is complex, and modern cars are equipped with computers that can detect faults. One common issue is the clogging of the Diesel Particulate Filter (DPF), which may trigger a warning on the instrument cluster. In such cases, a regeneration process can be used, or the car should be taken to a qualified mechanic for inspection and repairs.

Q4: How can I fix a fault in the emission control system?

Ans: Due to the complexity of the emission control system and the placement of its components, it is best to have any issues addressed by an experienced mechanic. DIY repairs are not recommended, as improper handling may lead to further complications.

Q5: Why might the emission control system not be ready?

Ans: Certain emission control components, like the catalytic converter and Exhaust Gas Recirculation (EGR) system, require specific operating conditions to function optimally. For instance, they may not work efficiently when the engine temperature is too low. Automakers often tune these systems to adapt to various environmental conditions, ensuring their effectiveness in diverse situations.

Conclusion:

Emission control systems play a crucial role in reducing harmful pollutants from vehicles and preserving the environment. Catalytic converters, evaporative emission control, EGR, DPF, and SCR are among the effective methods employed to achieve cleaner air and comply with emissions standards. By adopting and continuously improving these technologies, we can pave the way for a cleaner and more sustainable future.