What is the purpose of a Diesel Exhaust Fluid (DEF) system in modern diesel engines, and what happens if the system malfunctions or DEF is contaminated?

The purpose of a Diesel Exhaust Fluid (DEF) system in modern diesel engines is to reduce emissions of nitrogen oxides (NOx). NOx are harmful pollutants that contribute to smog and acid rain. The DEF system uses a process called Selective Catalytic Reduction (SCR) to convert NOx into harmless nitrogen and water. The DEF, which is a solution of urea in water, is injected into the exhaust stream upstream of the SCR catalyst. The heat from the exhaust causes the urea to decompose into ammonia. The ammonia then reacts with the NOx on the surface of the SCR catalyst, converting them into nitrogen and water. If the DEF system malfunctions, several problems can occur. The engine's NOx emissions will increase, potentially violating emissions regulations. The engine's performance may be reduced. Many engines are programmed to reduce power output or even shut down if the DEF system is not functioning properly. The DEF system components can be damaged. A malfunctioning DEF system can cause the SCR catalyst to overheat or become contaminated. If the DEF is contaminated, it can also cause problems. Contaminants in the DEF can clog the DEF injector, preventing it from spraying properly. They can also damage the SCR catalyst. Using DEF that is not the correct specification can also cause problems. For example, using DEF with too high a concentration of urea can damage the SCR catalyst. Using DEF with too low a concentration of urea will reduce the system's effectiveness. For example, if a wheel loader's DEF injector becomes clogged due to contaminated DEF, the engine may experience reduced power and the emissions control system will not function correctly. Therefore, proper functioning of the DEF system and the use of high-quality, uncontaminated DEF are crucial for meeting emissions regulations and maintaining engine performance.