What is a catalytic converter and how it works?
The catalytic converter is that component of the exhaust system, which results from the combustion of the fuel that “treats” the exhaust gases before they are exhausted. The normal operation of a catalytic converter leads to a conversion of the combustion gases into (almost) inoffensive gases thus helping in the fight against pollution.
A catalyst is capable of converting 98% of the harmful gases from the exhaust into cleaner gases. Inside the catalyst, the gas circulates through a dense honeycomb structure of ceramic and lined with catalysts and insulating layers.
The catalytic converter has the form of a classic, elliptical or round sound damper, inside which there is a ceramic or metallic monolith on which metals are deposited, which favors the conversion of polluting gases into non-polluting gases.
Why do cars need a catalytic converter?
To understand why catalysts are needed, we had to find out why engines cause pollution. The engines of the cars run on gasoline or diesel, which are made from petrol. Petrol is composed of hydrocarbons (molecules made of carbon and hydrogen atoms). In theory, the burning of any type of fuel based on hydrocarbons together with oxygen from the air, a large amount of energy is released. This results in carbon dioxide and water, elements relatively harmless to the atmosphere.
In practice, however, gasoline is a mixture of about 150 chemicals, not only hydrocarbons but also many additives. This means that gasoline doesn’t burn as clean as we would like. This results in pollution. The polluting gases resulting from engine engines include a poisonous gas called carbon dioxide, but also volatile organic compounds and nitrogen oxides.
Pollutant gases are composed of harmful molecules, but in turn, these molecules are composed of harmless atoms. The problem of pollution would be solved if there was a way to split these molecules after they leave the engine, before being released into the air. Here comes the catalyst, a simple device that uses chemical reactions to reduce the number of pollutants in the engine.
Most modern cars are equipped with triple-acting catalytic converters, which refers to the three regulated emissions whose reduction helps the catalyst – carbon monoxide, VOC and NOx molecules. The converter uses two different types of catalysts, a reduction catalyst, and an oxidation catalyst. Both types consist of a ceramic structure covered with a metal catalyst, generally platinum, rhodium and/or palladium. The idea is to create a structure that exposes a maximum surface area of catalyst to the exhaust stream while minimizing the amount of catalyst needed (catalysts are very expensive). The main parameters that influence the degree of conversion are:
- – the coefficient of excess air and its variation;
- – the temperature of the flue gas;
- – space velocity (flow rate of flue gas relative to the volume of the catalyst).
Currently, almost exclusively the trivalent or triple-acting (or three-way) catalyst with ceramic support is used. There are two main types of structures used in catalytic converters – honeycombs and ceramic balls. Most cars today use a honeycomb structure.
Can the catalytic converter reduce pollution even better?
The catalytic converter greatly reduces pollution, but this reduction can be substantially improved. One of the biggest drawbacks is that it only works at fairly high temperatures. When you start the machine from the cold, the catalytic converter does not work nearly at all to reduce the pollutants in the exhaust gas. A simple solution is to move the catalytic converter closer to the engine. Thus, hotter exhaust gases reach the converter and it heats up faster, but this solution can also reduce the life of the converter by exposing it to extremely high temperatures.
Most car manufacturers place the converter under the front passenger seats, far enough from the engine to keep the temperature at a level that will not damage it. Preheating the catalytic converter is a good method for reducing emissions. The easiest way to preheat the converter is to use electric heaters. Unfortunately, the 12-volt electrical systems on most cars do not provide enough energy or power to heat the converter quickly enough. Most people would not wait a few minutes for the catalytic converter to warm up before starting the car. Hybrid cars with large packages of high-voltage batteries provide enough power to heat the catalytic converter very quickly.
The efficiency of the catalyst transformations is optimal at high temperatures. The point at which the catalyst efficiency exceeds 50% is called the “catalyst ignition” point. For most catalysts, the ignition point is around the temperature of 250 … 300 ° C, for this reason, it is important that the catalyst temperature reaches the optimum operating value (400 … 800 ° C) as soon as the engine is started. Positioning the catalyst as close to the engine as possible on the exhaust manifold will facilitate faster heating.
To reach the optimum operating temperature, some catalysts are provided with heating resistors located before the metal monolith. Thus, at start-up, the electric resistor is powered by electricity and produces heat. The flue gases take up the heat emitted by the heating resistance and enter the catalyst accelerating the heating process.
Problems and symptoms of a bad catalytic converter
The catalyst may be damaged or even destroyed if it is operating at excessive temperatures. The very high temperatures in the exhaust manifold are caused by the unburnt air-fuel mixture that ignites in the catalyst. The combustion of the air-fuel mixture in the catalyst can raise its temperature to 1400 ° C. Exposure of the catalyst to high temperatures also influences its efficiency. If the temperature in the catalyst exceeds the value of about 1000 ° C it deteriorates irreversibly and over time, after multiple exposures, it does not convert the pollutant emissions.
2. Engine misfire
The main source of catalyst damage due to high temperatures is engine misfire. It occurs because of the following causes:
- – damaged spark plugs: the spark is no longer produced or is produced but with low intensity
- – the air-fuel mixture is too rich (acute lack of oxygen) or too poor (acute lack of fuel)
- – the cylinder loses compression
A misfired engine will feel, when idle, with strong shocks and vibrations, and at high speeds with low power. Due to the destructive effect that the ignition rates have on the catalyst, the OBD2 standard requires the diagnosis of this phenomenon. When this occurs, check engine light will be on and the engine may enter the damage regime (limited performance) to limit the destructive effect on the catalyst.
If you have a check engine light on the dashboard, be sure to read the trouble codes with an OBD2 scanner to see if you receive the P0420 error code because this error code occurs, most of the time when there are problems with the catalytic converter.
There are many situations in which the catalyst can become contaminated and as a result, it can no longer capture carbon emissions effectively. These situations include leakage of engine coolant or a scenario in which, due to oil burns, harmful particles reach the exhaust system.
If the engine burns too much oil, the oil additives can be deposited on the surface of the catalyst, sealing it. This prevents gases from coming into contact with the metals of the catalyst, which decreases its efficiency.
Contamination can also occur in situations where you make short but frequent, car trips. In this situation, the catalyst can regenerate after long driving.
In situations where the oil mixture is not the right one or the exhaust system does not operate at normal parameters, the catalyst may become clogged over time. Clogging can be prevented by maintaining and constantly observing vehicle emissions.
Among the most common signs of a faulty catalyst are: poor engine performance, low acceleration, black smoke or sulfur odor coming from the exhaust pipe, excessive heat under the vehicle, strange noises, increased fuel consumption.
How to clean a clogged catalytic converter
A clogged catalyst can result in high consumption, poor engine performance, but also poor control of harmful gas emissions. To repair the catalyst without taking the car to service, here are the steps you need to follow.
- Before you start, park your car on a hard, smooth and well-lit surface. Open the hood and prop it up to keep it open. Make sure you use eye protection.
- Use a wrench to remove the screws holding the catalyst in place, and don’t forget to put the screws in a secure place. Remove the catalyst from the exhaust system.
- Inspect the catalyst for defects. Shake it and listen if you hear any strange noises.
- Use a cloth and clean the residue on the surface of the catalyst. Use a hose with pressurized water to clean the deposits. If it is still dirty after these steps, let the catalyst soak it in a mixture of degreaser and hot water.
- Allow the catalyst to dry completely before reassembling it in the exhaust system.
- Another way to clean the catalyst and avoid damaging deposits is to use better quality fuel. For example, if you normally use the cheapest fuel, try passing through a few fuel tanks of the highest quality fuel.
How to repair a catalyst that is making strange noises
When a catalyst breaks down, the monolithic filler in the substrate breaks and the parts begin to shake and make noises. Since the substrate is the one that absorbs the toxic gases, the longer you delay its decomposition, the better for your car. The best way to do this is to use a mechanic’s stethoscope to find out exactly where the spare parts are. Give a small hole at each location and fasten with screws. These will replace the detached parts and delay the replacement of the catalyst.
It is also possible that the heat shield of the catalyst will start to make some noises. You can solve the problem easily by putting more hose clamps together to form a larger hose clamp around the shield. Fix it until you think it is tight enough to hold the shield in place.
If you have exhausted all the solutions in repairing the catalytic converter, then it is necessary to replace it.
The costs of replacing the catalytic converter
If you conclude that you need a new catalyst, you should know that prices vary greatly depending on the vehicle model, age, or whether the part is new or used. These can exceed $ 500. In terms of labor, it costs on average between 80 $ and 300 $.
How to clean the catalytic converter without removing it
If you want to try to clean the catalytic converter without removing it from the machine, you can try the Catacleaner. This is a very good solution for any car, whether it is diesel, gasoline, or hybrid. Catacleaner not only plays an important role in cleaning the catalytic converter, but it will also clean the oxygen sensors, but also the entire exhaust system of the car.
Important to know is that this product cannot remedy the mechanical defects that are inside the catalytic converter, if it is very hard, cracked or broken. OXICAT is a solution for cleaning the catalytic converter, which can run with some oil burns before.
For the solution to do its job, it is important to add the specified amount of OXICAT in the car tank, and then you have to drive the car a few miles to find out if the car can be driven better than before. It is again important to know that the temperature of the coolant of the car must be checked permanently, and thus you will know for sure that there is no problem of overheating.