What are the reasons for excessive NOx emissions in cars?
3 Answers
The reasons for excessive NOx emissions in car exhaust are as follows: 1. Vehicle aging. If the vehicle has traveled more than 450,000 kilometers or has been in use for more than 15 years, various components of the car will show significant aging, poor contact, poor sealing, and insufficient pressure. 2. Failure of the three-way catalytic converter. This is the most important external purification device installed in the car's exhaust system, which can convert harmful gases such as CO, HC, and NOx in car exhaust into harmless carbon dioxide, water, and nitrogen through oxidation and reduction reactions. 3. Abnormal engine operation. The engine may have issues such as spark plug oil leakage or oil mixing. When the throttle is increased, the engine does not run smoothly and powerfully. 4. Damaged oxygen sensor. In engines using a three-way catalytic converter to reduce exhaust pollution, the oxygen sensor is an essential component. It detects the oxygen concentration in the exhaust and sends feedback signals to the ECU, which then controls the increase or decrease of fuel injection by the injector, thereby keeping the air-fuel ratio of the mixture near the theoretical value and making fuel combustion more efficient.
Our family has been driving for over a decade, and I've found that NOx emissions exceeding standards generally stem from two major reasons. One is when you frequently floor the accelerator while driving, causing the engine temperature to spike suddenly, especially during prolonged high-speed driving—nitrogen oxides are produced under such high-temperature conditions. The other is when key components in the car, like the three-way catalytic converter or the EGR system, become aged or clogged with carbon deposits, rendering them ineffective. The three-way catalytic converter is supposed to help break down pollutants, but once it gets blocked or fails, NOx levels become uncontrollable. If the EGR valve gets clogged with carbon deposits, the exhaust gas recirculation is disrupted, leading to higher exhaust valve temperatures and skyrocketing NOx emissions. Additionally, if the vehicle's oxygen sensor malfunctions, the air-fuel ratio gets messed up, also increasing NOx. Personally, I recommend not waiting for problems to arise before fixing them—regularly check the emission system, especially for older cars. A simple cleaning can prevent a lot of trouble, since environmental protection relies on daily habits.
As someone who enjoys tinkering with cars, I believe excessive NOx emissions are often related to routine maintenance. The most common issue is a clogged catalytic converter—carbon buildup inside prevents it from processing NOx, so regular cleaning with a detergent is necessary. The EGR system is also prone to problems; if the valve gets dirty and doesn’t seal properly, high-temperature exhaust gases can’t recirculate, causing combustion chamber temperatures to rise and NOx production to spike. A faulty oxygen sensor leads to inaccurate air-fuel ratio adjustments, resulting in incomplete combustion and higher emissions. Additionally, excessive carbon buildup in older components like the intake manifold or fuel injectors disrupts smooth engine operation, naturally increasing NOx. When driving, avoid aggressive acceleration—smooth driving reduces high-temperature conditions. In short, preventing minor issues is far better than fixing them later. Checking these components during oil changes and spending a little money can help protect the environment.
