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EXHAUST SMOKE: TYPES (BLACK, WHITE, AND BLUE) AND CAUSES

Exhaust smoke is a way of your car communicating with you to say what is wrong. Usually, the smoke that gets emitted is black, white, grey and blue. The exhaust gases are an old school way to detect symptoms of problems i.e. large amounts of black smoke may mean the EGR is blocked and it’s over-fueling.
Knowing the difference between the smokes that comes from the exhaust is very useful. If you are not going to fix the car yourself, take note when the smoke appears and the color and report back to your mechanic. Avoiding the problem will only shorten the life of the engine and result in unnecessary repair bills.

TYPES OF EXHAUST SMOKES

1. White smoke
2. Black smoke 
3. Blue smoke

1. WHITE SMOKE

Thick white smoke can be caused by the engine burning coolant. This can be caused by the coolant leaking into the engine due to a leak in the head gasket, a damaged cylinder head or a cracked engine block. If you happen to see this kind of smoke take your car to the garage as soon as possible as the leaking coolant can lead to overheating which could cause damage to your engine. Not to mention chances of coolant mixing with the oil.
White smoke has a varying amount of causes and symptoms, which are more common in gasoline cars. The most common cause of white smoke is when the car has just been started. The white smoke is just steam from condensation that clears as the car warms up.

White Smoke from Petrol/Gasoline Car

White smoke as mentioned is usual from startup however if it continues when warm, you have a problem. Check the following for white smoke causes in petrol cars:

1. Head Gasket Failure.

A common issue with cars that have been neglected or simply the gasket has reached the end of its lifespan. Try using a head gasket sealer and testing to see if any smoke appears and you would have located the issue.

2. Turbo Issues

The turbo usually emits white or grey smoke that mostly appears under acceleration. Not as common but seals and pumps do fail and turbos problems get worse with old age.

3. Overheating Engine.

In some cases, certain engines tend to bellow out white smoke when they are too hot. Check the temperature next time there is white smoke. If it is overheating, look into potential causes, such as broken fans or no water.

4. Cracked Engine Block.

Not that common but a cracked engine block will force white smoke to the exhaust. This sort of damage to the block can cause a car to become written off by the insurance companies.

White Smoke from Diesel Car

Sadly, white smoke from a diesel car operating at its optimum temperature is bad news in most cases. Check for the following for white smoke in diesel cars:

1. Worn or Leaking Injectors.

The seals on the fuel injectors are prone to breaking down and eventually leak. This can cause a blueish/white smoke to bellow from the exhaust. Take a look on your engine bay to see if there are any signs of leakage, usually in the form of black carbon build-up.

2. Poor Quality Diesel.

Often poor quality fuel can cause a blueish mix of white smoke to emit from the exhaust. It’s always best to use high-quality injector cleaner to treat your diesel fuel.

3. Low Cylinder Compression.

Usually caused by other components such as piston rings becoming worn out

2. BLACK SMOKE

Black smoke that gets emitted from a car is more common in diesel cars. Apart from when the car is cold, white smoke should never appear from a diesel car exhaust. The majority of older diesel cars will bellow black smoke under heavy acceleration but new diesel engines will not emit any black smoke.

Black Smoke from Petrol/Gasoline Car

Black smoke in petrol/gasoline cars will is often the result of a rich mixture from the distributor. This will result in very poor miles per gallon and extra stress on engine components.

1. Rich Mixture.

A rich fuel mixture or air mixture will cause black smoke under acceleration or revving. This can be a result of a distributor unit providing too much fuel to the injectors or not enough air getting to the fuel. Some cars are tuned to run rich such as the Mitsubishi Evo.

2. Not Enough Air.

A clogged air filter or not enough air getting to the intake system completely offset the air to fuel ratio.
Petrol engines very rarely emit black smoke from the exhaust compared with diesel cars. In almost all circumstances, black smoke from a petrol car is due to the air to fuel ratio.

Black smoke from a diesel car

Black smoke from a diesel car is the result of poor combustion of the fuel. In my experience, the issue is either due to insufficient airflow or poor quality diesel that builds up into a carbon deposit. Causes of black smokes from diesel car exhausts are the following:

1. Clogged Air Filters

With dust blocking the air filter, there are chances that sufficient air amount is not reaching the cylinder. As a result, more fuel is being burnt. And, ultimately this causes black smoke from exhaust irrespective of the fact that the fuel injectors are working properly.
Besides this, due to the heavy load or during hard acceleration also black smoke can be found, as the fuel is not injected at the right time.

2. Damaged Fuel Injectors

In case of the good fuel injector, the fuel is properly atomized, which means the fine droplets of fuel are spreading equally in the cylinder. However, if the injectors don’t close on time or they are clogged, there are chances that more fuel is injected in a certain area called a rich mixture area of the car. In this situation, even the amount of air is insufficient for the combustion of fuel due to blocked injectors (and the few opened ones inject only fuel).
As a result, solid carbon is formed from the fuel not burnt, which is emitted as black smoke from the tailpipe of the car.

3. Faulty MAF Sensors

The work of the Mass Airflow sensor is to determine the volume of air entering the engine, which in turn, helps in measuring the amount of fuel to be injected inside the cylinder. This entire functioning is important for the complete combustion of fuel in the engine. Otherwise, a malfunctioning MAF sensor can lead to poor performing engine.

4. Bad EGR Valve

The EGR reduces the emission of nitrogen oxides by a re-circulating portion of an engine’s exhaust gas to the internal combustion engine. If this component is damaged, it emits all the black smoke out of the exhaust.

5. Damaged Piston Rings

One possible reason behind black smoke from the exhaust pipe is damaged piston rings. Piston Rings are designed to prevent the infiltration of engine oil inside the combustion chamber. If there is any problem with the piston rings, the engine oil starts flowing into the combustion chamber. The combustion of the mixture of this engine oil and the fuel delivers black smoke.

6. Engine Deposits

Engine deposits are another reason causing black smoke from the tailpipe. When the engine is new, it will run fluently without any problems. But after a long period of use, the engine conditions get worse and worse and this consists of getting accumulations of combustion product in important areas like combustion chambers and injectors. And these interfere with the best functioning.

7. Poor Quality Diesel Fuel.

Poor quality fuel will also cause black smoke (as well as white) to come from the exhaust. Using a diesel additive to clean vital components can fix this problem, which we recommend to do on a full tank basis.

8. Faulty Turbocharger and Bad Air to Fuel Ratio.

Diesel fuel requires an adequate air ratio in order to perform as it should from the factory. The poor ratio is usually caused through a faulty turbo, dirty/old air filter and sensors that control airflow. With bad air to fuel ratio, performance will be reduced significantly.

9. Over Fueling or ECU Chip/Tuning/Remap.

The term basically means that too much diesel is being pumped from the fuel pump. This has the potential to crack a cylinder head if it’s over fueling excessively. However, if the diesel car has been tuned or remapped, over-fueling (and over boosting) is common. I had a 1.9 TDi that was remapped, which would leave a black smokescreen in my rear mirror under heavy acceleration.

3. BLUE SMOKE

Blue smoke is an indication that the car is burning engine oil. This happens when the piston rings are worn out and oil is leaking to the combustion chamber where it is burned together with the fuel. For a turbocharged car, the smoke is a sign that the blower is in need of replacement. Burning oil can cause rough starts due to the fact that it can ruin a car’s spark plugs.

1. Stuck PVC Valve

If you observe blue smoke appearing in your car all the time, PCV (Positive Crankcase Ventilation) Valve will be the first thing you should check. The function of the PCV valve is releasing the pressure (which builds up in the Oil Pan) into the Intake Manifold (where the engine gets its air for running). The Intake Manifold is linked to the Air Filter of your engine too. So if the PCV Valve gets stuck, it will keep mixing the oil with air and other gases inside the engine. The combustion of this mixture will cause blue smoke.

2. Worn Engine

The worn engine is another culprit responsible for blue smoke from the exhaust.
Each engine has pistons which are moved up and down a cylinder. Each piston has metal rings around its side like bracelets. The function of these rings is to help the piston forming a tight seal against the cylinder. So if the rings or cylinder is worn out, oil from below the piston will come up. Then the oil gets mixed with the Air and Gasoline and gets burnt, causing the blue smoke.

3. Blown Turbo

Blown turbo is a probable reason causing blue smoke in cars that have Turbos. Blue smoke will suddenly appear in a big cloud if your car blows a Turbo. A blown turbo is either the turbo casing has damaged or a broken oil seal in the Turbo. In both cases, they let oil into the intake of the engine.

4. Blue Smoke Comes With Transmission Fluid Loss

A modulator is used to control the transmission shift in older vehicles with vacuum controlled automatic transmissions. If there is any problem with the modulator like a failed diaphragm, it enables the engine to suck in transmission fluid. Then this transmission fluid will be burnt like oil, creating the blue smoke coming out of the exhaust.

EXHAUST SYSTEM: COMPONENTS AND THEIR FUNCTION

The exhaust system collects the exhaust gases from the cylinders, removes harmful substances, reduces the level of noise and discharges the purified exhaust gases at a suitable point of the vehicle away from its occupants…

FUNCTION

The exhaust system collects the exhaust gases from the cylinders, removes harmful substances, reduces the level of noise and discharges the purified exhaust gases at a suitable point of the vehicle away from its occupants. The exhaust system can consist of one or two channels depending on the engine. The flow resistance must be selected so that the exhaust back pressure affects engine performance as little as possible. To ensure that the exhaust system functions perfectly, it must be viewed as a whole and developed accordingly. This means that its components must be coordinated by the design engineers in line with the specific vehicle and engine.

In addition to all the complex functions which the exhaust system has to perform, it is also subject to extreme stresses. The fuel-air mixture in the cylinders is abruptly heated to temperatures up to 2,400 °C. This causes it to expand greatly before escaping into the exhaust system at supersonic speed. This noise level resembles the crack of an explosion and must be reduced by approx. 50 dB(A) as it travels from the engine exhaust valve to the end of the exhaust system.

Apart from temperature and pressure stresses, the exhaust system must also cope with vibrations from the engine and bodywork as well as vibrations and jolting from the carriageway. The exhaust system additionally has to resist corrosion attacking from the inside caused by hot gases and acid, and from the outside in the form of moisture, splashed water and salt water. There is also the risk that the catalyst may be poisoned through sulfur or lead present in the fuel.

COMPONENTS OF EXHAUST SYSTEM

1. Exhaust manifold:

The exhaust manifold attaches to the cylinder head and takes each cylinder’s exhaust and combines it into one pipe. The manifold can be made of steel, aluminum, stainless steel, or more commonly cast iron.

2. Oxygen sensor:

All modern fuel injected cars utilize an oxygen sensor to measure how much oxygen is present in the exhaust. From this, the computer can add or subtract fuel to obtain the correct mixture for maximum fuel economy. The oxygen sensor is mounted in the exhaust manifold or close to it in the exhaust pipe.

3. Catalytic converter:

This muffler like part converts harmful carbon monoxide and hydrocarbons to water vapor and carbon dioxide. Some converters also reduce harmful nitrogen oxides. The converter is mounted between the exhaust manifold and the muffler.

Selective Catalytic Reduction (SCR)

This technology uses ammonia to break down dangerous NOx emissions produced by diesel engines into nitrogen and water. In automotive applications, SCR delivers ammonia through a urea solution – Diesel Exhaust Fluid (DEF) – which is sprayed into the exhaust stream by an advanced injection system and then converted into ammonia on a special catalyst.

SCR is the technology of choice for the majority of truck and engine manufacturers to meet 2010 emissions standards for heavy-duty trucks.

Aside from helping the environment, the biggest benefit of SCR for vehicle owners is the fuel efficiency the technology provides. Because SCR deals with emissions in the exhaust pipe, engineers are able to tune the engine to provide more torque and reduce fuel consumption.

4. Muffler/Silencer:

Every internal combustion engine produces «exhaust noise» due to the pulsating emission of gases from the cylinders. This noise has to be silenced by reducing the sound energy of the exhaust gas flow. There are two basic options here: Absorption and reflection of the sound in the silencer. These two principles are generally combined in a single silencer. Exhaust chambers and exhaust flaps are other sound-absorbing and sound-modifying elements that can be used to eliminate especially undesirable frequencies from the outlet noise. Catalytic converters also have a sound-absorbing effect.

The exhaust system is itself a system subject to vibration, it produces noise itself through natural frequencies and vibration which are transmitted to the car body. Careful coordination of the entire system is, therefore, necessary here. This includes the design and positioning of the individual elements of the exhaust system and their flexible mountings.

The muffler serves to quiet the exhaust down to acceptable levels. Remember that the combustion process is a series of explosions that create a lot of noise. Most mufflers use baffles to bounce the exhaust around dissipating the energy and quieting the noise. Some mufflers also use fiberglass packing which absorbs the sound energy as the gases flow through.

5. Resonator

The muffler alone cannot always quiet all the engine noise. Many exhaust systems also include a resonator which is like a mini-muffler. They are usually straight pipes filled with sound muffling materials. The resonator can be either before or after the muffler in the exhaust system.

6. Exhaust pipe:

Between all of the above mention parts is the exhaust pipe which carries the gas through it’s journeys out your tailpipe. Exhaust tubing is usually made of steel but can be stainless steel (which lasts longer due to its corrosion resistance) or aluminized steel tubing. Aluminized steel has better corrosion resistance than plain steel but not better than stainless steel. It is, however, cheaper than stainless steel.

HOW TO IDENTIFY PROBLEMS

Although the exhaust system is located underneath the vehicle, there are some symptoms you can look out for which may indicate that there is a problem with your exhaust.

1.Noises

A loud roaring noise could indicate corrosion to the exhaust system
A hissing sound could mean that gas is escaping through a crack or hole in one of the exhaust components
Chugging noises mean that there may be a blockage in one of the pipes
A persistent and rapid succession of knocking sounds indicate that a part of the exhaust may have come loose

2. Emissions

White smoke – this is not smoke but in fact, vapor and you should see this when you first start your car as it indicates that the engine is warming up. If white smoke is visible after the engine is warm it may indicate internal leaks or cracks.

Blue smoke – A bluish-grey smoke means that oil may be burning in the combustion chamber. This could mean that the cylinder is worn or there are leaks in the valve seals.

Black smoke – very black smoke is often accompanied by increased fuel consumption and may signify leaks in the exhaust system or a problem with the engine.

3. Visual

Inspect the components of your exhaust that you can see for any signs of rust or corrosion. Make sure you keep an eye out for any cracks and holes and contact a specialist if you do find any signs of damage.

En los motores más modernos, el funcionamiento de la EGR se rige por la señal de los sensores de temperatura del motor, régimen del motor y carga de aceleración. En función de estos la ECU del coche comandará la EGR, abriéndola o cerrándola. Por norma general, las EGR están abiertas (metiendo gases quemados al motor) cuando circulamos con el motor caliente, a baja carga y a regímenes de motor bajos.

Si se cumplen los parámetros para la apertura de la EGR, veremos que esta se acciona de dos formas, según su naturaleza. Puede ser por un actuador de vacío o por un actuador eléctrico. Las segundas son las más eficaces y las que ahora equipan casi todos los vehículos, ya que permiten controlar mejor el grado de apertura de la válvula. Algunos vehículos equipan válvulas EGR refrigeradas por un intercambiador de calor que utiliza el refrigerante del motor. De esta forma, se reduce la temperatura de los gases a la hora de introducirlos en los cilindros y la producción de emisiones de NOx es todavía menor.

Cuando la válvula EGR está abierta en la cámara de combustión se mezclan los gases recirculados con los gases frescos de la admisión. En este caso los segundos son menores que si la válvula estuviese cerrada y por tanto en las explosiones se genera menos calor, de ahí la reducción de las emisiones de NOx.

Como no es difícil intuir, el funcionamiento la válvula EGR resta potencia al motor. Cuanto más frío sea el aire que entra al motor y más oxígeno tenga, más potencia tendrán las explosiones y por tanto, mejor será el rendimiento del vehículo. Por ese motivo, cuando demandamos mucha aceleración, la EGR permanece cerrada, para tener todas las prestaciones del motor.

Diesel engines tend to emit higher Nitrogen Oxide (NOx) which is harmful to humans. This is because of high temperatures in the engine cylinders because of the higher compression ratio. To control and decrease the NOx, manufacturers employ ‘Exhaust Gas Recirculation’ technology in engines.

The term EGR stands for Exhaust Gas Recirculation. It is a part of modern-day diesel engine vehicles which helps to decrease the Nitrogen Oxide (NOx) emissions. Exhaust Gas Recirculation is the technique used for reducing the nitrogen oxide in both the internal combustion diesel engines as well as petrol engines.

WORKING PRINCIPLE

The exhaust gas added to the fuel, oxygen, and combustion products increases the specific heat capacity of the cylinder contents, which lowers the adiabatic flame temperature.

In a typical automotive spark-ignited (SI) engine, 5% to 15% of the exhaust gas is routed back to the intake as EGR. The maximum quantity is limited by the need of the mixture to sustain a continuous flame front during the combustion event; excessive EGR in poorly set up applications can cause misfires and partial burns. Although EGR does measurably slow combustion, this can largely be compensated for by advancing spark timing. The impact of EGR on engine efficiency largely depends on the specific engine design, and sometimes leads to a compromise between efficiency and NOx emissions. A properly operating EGR can theoretically increase the efficiency of gasoline engines via several mechanisms:

• Reduced throttling losses.

The addition of inert exhaust gas into the intake system means that for given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses.

• Reduced heat rejection.

Lowered peak combustion temperatures not only reduces NOx formation, but it also reduces the loss of thermal energy to combustion chamber surfaces, leaving more available for conversion to mechanical work during the expansion stroke.

• Reduced chemical dissociation.

The lower peak temperatures result in more of the released energy remaining as sensible energy near TDC (Top Dead-Center), rather than being bound up (early in the expansion stroke) in the dissociation of combustion products. This effect is minor compared to the first two.

EGR is typically not employed at high loads because it would reduce peak power output. This is because it reduces the intake charge density. EGR is also omitted at idle (low-speed, zero loads) because it would cause unstable combustion, resulting in rough idle.

Since the EGR system recirculates a portion of exhaust gases, over time the valve can become clogged with carbon deposits that prevent it from operating properly. Clogged EGR valves can sometimes be cleaned, but replacement is necessary if the valve is faulty.

DESIGN

A vacuum controlled EGR valve regulates the number of exhaust gases admitted into the cylinders. It consists of a spring-loaded vacuum diaphragm. It links to a metered valve which controls the passage of the exhaust gases. Ported vacuum from a calibrated signal port located above the throttle valve connects to the EGR vacuum chamber.

At idling, the EGR valve is in the closed position because of the spring pressure and lower ported vacuum. The engineers designed it so because if the exhaust gases recirculate at the idling, then it would cause rough/erratic idling. Upon opening of the throttle applies the ported vacuum and gradually opens the tapered valve. This causes the exhaust gas to flow into the intake manifold.

However, when the throttle opens fully, there is no vacuum in the intake manifold. So, it closes the tapered valve and stops the exhaust gases from entering the intake manifold.

BENEFITS

The Exhaust Gas Recirculation system recirculates a part of the exhaust gas back into the engine cylinders through the combustion chamber. The logic behind the EGR system is very simple. The exhaust gas is hotter than the fresh air sucked by the engine. So, the exhaust gas significantly reduces the contents of the cylinder for combustion. Because of the absence of oxygen (O2), the exhaust gases have nothing to burn as they contain neither fuel nor oxygen particles.

Thus, it results in lower heat discharge and cylinder temperatures. It reduces the formation of nitrogen oxide (NO2) as well. The dormant exhaust gas present in the cylinder also limits the peak temperatures. It also reduces the loss that arises because of throttling in petrol engines while improving the engine life by reducing the cylinder temperatures. The three-stage catalytic converter further reduces the NOx to acceptable levels.

LIMITATIONS

The engineers designed the EGR system in such a way that it recirculates the exhaust gases only when the engine forms the Nitrogen Oxide (NOx). Thus, the EGR system DOES NOT affect the ‘Full-Load’ operation.

The Exhaust Gas Recirculation system also has a thermal control valve in the vacuum line which prevents the operation of EGR at lower engine temperatures. This system is useful especially in the diesel engines where the catalytic converter cannot stimulate the chemical reduction due to high oxygen contents. So, the NOx emission remains the same in such conditions.}

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