What are the main harmful substances emitted by diesel engines?

[Mila]

The main harmful substances emitted by diesel engines are: nitrogen oxides and particulate matter. The working principle of a diesel engine is: 1. Intake stroke: The crankshaft rotates, the exhaust valve closes and the intake valve opens, the piston moves downward from the top dead center, the cylinder volume increases and the pressure decreases, air is drawn into the cylinder through the intake valve, and the piston moves downward to the bottom dead center; 2. Compression stroke: The crankshaft continues to rotate, forming a closed volume in the cylinder. As the piston moves upward, the pressure and temperature continuously rise; 3. Power stroke: Diesel is atomized and mixed with air through the high-pressure fuel injection pump and injector, forming a combustible mixture, which is injected into the cylinder with high-pressure and high-temperature gas, and combustion releases heat; 4. Exhaust stroke: The rotating crankshaft drives the connecting rod piston to move from the bottom dead center to the top dead center, and under the push of the piston, the exhaust gas is discharged from the exhaust valve.

[DelMakayla]

Diesel engines emit a significant amount of harmful substances when running, with nitrogen oxides being a major component. These can irritate the respiratory tract and contribute to smog formation. There are also those black, sooty particles containing carbon soot and polycyclic aromatic hydrocarbons, which are harmful if inhaled. Additionally, diesel fuel contains sulfur, which turns into sulfur dioxide after combustion—that pungent smell is its doing. Although diesel engines emit less carbon monoxide, excessive accumulation can still cause dizziness and poisoning. Modern vehicles now use urea systems and particulate filters to reduce these emissions. Older vehicles emitting thick black smoke are a clear sign of excessive particulate matter, so it's best to check the exhaust treatment system before hitting the road.

[DiViolet]

From an environmental perspective, each harmful substance emitted by diesel engines poses different hazards. Nitrogen oxides degrade air quality and harm trees and plants. The ultrafine particles in particulate matter can penetrate lung alveoli, and long-term inhalation may easily trigger asthma. The polycyclic aromatic hydrocarbons emitted by diesel vehicles are highly carcinogenic, and these components are also found in barbecue smoke. Acid rain produced by burning sulfur-containing diesel is most damaging to buildings, as stone carvings and metals cannot withstand the corrosion. Fortunately, the sulfur content in diesel sold at gas stations is now controlled below ten milligrams, so using high-quality fuel is the first step toward environmental protection. Regularly cleaning the fuel system and replacing filters can help the engine burn cleaner, naturally reducing emissions.

[LeHadley]

I've been driving a diesel pickup for five or six years, and I'm most familiar with the black smoke coming out of the exhaust pipe. The mechanic said that black smoke is actually particulate matter, mostly caused by clogged fuel injectors or a dirty air filter. Also, the exhaust gas analyzer often indicates high nitrogen oxide levels, which is related to driving habits. It improved a lot after I stopped stomping on the accelerator. Last winter, I was even pulled over by the traffic police for emitting white smoke. The inspection found that the exhaust gas recirculation valve was stuck, resulting in sulfur dioxide smell in the exhaust. Now, during every maintenance, I ask the mechanic to focus on checking the EGR valve and urea injector, as it directly affects whether the vehicle can pass the annual inspection.

[OAlina]

Diesel vehicle emission management has several technical countermeasures in place. For nitrogen oxides (NOx), the primary solution is the SCR (Selective Catalytic Reduction) system, which uses urea injection to break them down. Particulate matter is captured by ceramic DPF (Diesel Particulate Filter) traps, and the accumulated soot is burned off during regeneration. The engine control unit improves atomization through common-rail injection, reducing soot formation. Newly developed lean-burn technology can increase fuel efficiency to over 40%, naturally lowering emissions. However, vehicle maintenance is crucial—using the correct oil grade and maintaining catalytic converter activity is essential; otherwise, the exhaust treatment system may fail prematurely. The EU's Euro 6D standard requires NOx emissions to be reduced to below 80 milligrams per kilometer, nearly ten times lower than older vehicles.

[DelEmerson]

Anyone who has driven a diesel car knows that the exhaust pipe gets extremely hot to the touch, and this high-temperature oxidation produces nitrogen oxides. The blue smoke during cold starts is actually unburned hydrocarbons, which smell like paint. I always remind my neighbors to change the diesel filter regularly; otherwise, the fuel injection pump won’t maintain proper pressure, and particulate emissions will double. The black smoke from heavy-duty trucks is the most obvious—it’s the result of an overly rich air-fuel mixture burning incompletely. Don’t just go for the cheapest gas station when filling up; diesel with high sulfur content produces sulfur compounds when burned. Nowadays, cities have installed many remote exhaust monitoring stations, and vehicles exceeding emission limits will be directly flagged, with fines and repairs costing far more than regular maintenance.