Analyze Exhaust Emission
Normally when in the workshop, all Tune-Up, while ending with the term Set / Check CO.
Not
just about the problem of environmental pollution, but from the
emissions test we can find out if there is damage to the car and of
course we could make fuel efficient.
In
support of environmental preservation efforts, the countries in the
world are starting to realize that the vehicle exhaust is one pollutant
or source of air pollution largest therefore, vehicle exhaust gases must
be made as much as possible so as not to pollute the air.
In
countries that have vehicle emission standards are tight, there are
five elements in vehicle exhaust gases to be measured are compounds HC,
CO, CO2, NOx compounds O2dan. While in countries that are not too
stringent emission standards, measuring only 4 elements in exhaust gases
are compounds HC, CO, CO2 and O2.
Hydrocarbon Compounds Emissions
Gasoline
is a hydrocarbon compound, so every HC obtained in vehicle exhaust
indicates unburned gasoline and wasted along with the rest of the
combustion. If a perfect burnt hydrocarbons (reacting with oxygen) then
the result of the combustion reaction is carbon dioxide (CO2) and water
(H¬2O). Although the ratio between air and fuel (AFR =
Air-to-Fuel-Ratio) is appropriate and supported by the design of the
combustion chamber when the engine is already close to the ideal, but
still, most of the gas as if still can â € œbersembunyiâ €? ? of fire
during a combustion process and cause the HC emissions at the tailpipe
is quite high.
For
a car that is not equipped with a catalytic converter (CC), HC
emissions that can be tolerated is 500 ppm and for cars equipped with
CC, HC emissions that can be tolerated is 50 ppm.
The
HC emissions can be reduced by providing additional heat and oxygen
outside the combustion chamber to complete the combustion process.
Oxygen injection process right after the exhaust port will be able to
suppress the HC emissions drastically. Currently, some car engines are
equipped with electronic water pump direct-injection reaction works when
cold-start to reduce HC emissions CC shortly before reaching the ideal
working temperature.
If
the high HC emissions, shows there are 3 possible causes that CC does
not work, AFR improper (too rich) or gasoline does not burn completely
in the combustion chamber. If the car is equipped with CC, it must be
tested prior to the CC denganc fig measure the temperature difference
between inlet and outlet CC. Supposedly the temperature at the outlet
will be at least 10% higher than inletnya.
If
CC works normally but HC stays high, then it is a symptom that AFR
improper or misfire occurs. AFR is too rich will cause the emission of
HC is high. This bias is caused partly leak fuel pressure regulator,
carburetor settings are not appropriate, a clogged air filter, engine
temperature sensor is not normal and so on that can make the AFR is too
rich. Dirty injectors or fuel pressure that is too low can make gasoline
granules become too big to burn dengna perfect and it also will make HC
emissions is high. Whatever the reason, which is too rich AFR also be
made into a high CO emissions and even lead to the outlet of the CC
overheated, but high CO and HC can also be caused by rembasnya lubricant
into the combustion chamber.
If
only high HC, it should explore the causes that make the ECU ordered
petrol injectors to spray just a little so that the AFR is too thin that
causes intermittent misfire. In cars still use carburetors, among other
causes misfire is not a good spark plug wires, ignition timing is too
backward, air leaks around the intake manifold or mechanical problems
that cause low engine compression numbers.
For
cars equipped with EFI system and CC, this misfire symptoms should be
addressed immediately because if allowed to stand, the ECU will
continuously strive to make AFR become rich as read that there is still
unburned oxygen. Consequently CC will overheat.
Emissions of Carbon Monoxide (CO)
Carbon
monoxide gas is a gas that is relatively unstable and tend to react
with other elements. Carbon monoxide, can be changed easily to CO2 with
the help of a little oxygen and heat. When the machine is working with
the appropriate AFR, emissions of CO in the exhaust end of the range of
0.5% to 1% for machines equipped with injection systems or approximately
2.5% for machines that still use carburetors. With the help of water
injection system or CC, the CO can be made as low as possible close to
0%.
If
the AFR little richer than the ideal figure (ideal AFR = lambda =
1.00), the CO emissions will rise dramatically. So high rates of CO
indicate that AFR is too rich, and this could be due to, among others,
due to problems in the fuel injection system such as the fuel pressure
is too high, the engine temperature sensor is abnormal, a dirty air
filter, PCV system is not normal, dirty carburetor or improper settings.
Emissions of Carbon Dioxide (CO2)
CO2
concentrations indicate directly the status of the combustion process
in the engine. The higher the better. When AFR is in an ideal figure,
CO2 emissions ranged from 12% to 15%. If the AFR is too lean or too
rich, then the CO2 emissions will drop drastically. If CO2 is below 12%,
then we have to look at other emissions that indicates whether the AFR
is too rich or too thin.
Keep
in mind that this is only a source of CO2 combustion chamber and CC. If
CO2 is too low but the CO and HC normal, indicating leakage of exhaust
pipe.
Oxygen (O2)
The
concentration of oxygen in the exhaust gases of vehicles is inversely
proportional to the concentration of CO2. To get a more complete
combustion process, the amount of oxygen into the combustion chamber
should be sufficient for any hydrocarbon molecules.
In
the combustion chamber, a mixture of air and gasoline can burn
perfectly if the shape of the combustion chamber curved perfectly. This
condition allows the molecules of gasoline and air molecules can be
easily met to react perfectly to the combustion process. But
unfortunately, the combustion chamber can not be perfectly curved and
smooth so as to allow the gas molecules as if hiding from molecular
oxygen and cause the combustion process to be completed.
To
reduce HC emissions, then it takes a little extra air or oxygen to
ensure that all gas molecules can â € œbertemuâ € ?? with molecular
oxygen to react perfectly. This means AFR of 14.7: 1 (lambda = 1.00) is
actually a condition that is a little thin. This is what causes the
oxygen in the flue gas will range between 0.5% to 1%. On machines
equipped with CC, this condition will be good because it helps the CC
function to convert CO and HC into CO2.
The
machine can still work well although AFR AFR too thin even to reach 16:
1. But in these conditions will arise other effects such as machines
tend knocking, engine temperature increases and emissions of NOx
compounds will also increase dramatically.
Normally
the concentration of oxygen in the exhaust gas is approximately 1.2% or
less even possible 0%. But we must be careful when oxygen concentration
reaches 0%. This shows that can be used up all the oxygen in the
combustion process and this can mean that tend to be rich AFR. In such
conditions, the low oxygen concentration will coincide with high CO
emissions. If the high oxygen concentration can mean AFR too thin but
also can indicate some other things. When coupled with high CO and HC,
then the car is equipped with CC CC means damaged. For a car that is not
equipped with the CC, when oxygen is too high and the other low means
there is a leak in the exhaust sytem.
Emissions of NOx compounds
In
addition to the above four gas, NOx emissions are not overlooked in
making the diagnosis of the machine. NOx compounds are chemical bonds
between nitrogen and oxygen. Under normal conditions the atmosphere,
nitrogen is an inert gas that is very stable which will not bind with
other elements. But under conditions of high temperature and high
pressure in the combustion chamber, the nitrogen will break ties and
binds with oxygen.
NOx
compounds is very unstable and when released into the air, will bind
with oxygen to form NO2. This is very dangerous because these compounds
are highly toxic, and when exposed to water to form nitric acid.
The
high concentration of NOx compounds due to the high oxygen
concentration coupled with the high temperature of the combustion
chamber. To keep the NOx concentration is not high, it is necessary to
precisely control the temperature of the AFR and combustion chamber must
be maintained so as not too high either with EGR and long valve
overlap. Normally NOx at idle does not exceed 100 ppm. If the AFR is too
thin, the ignition timing is too high or other causes which led to the
combustion chamber temperature increases, will increase the
concentration of NOx and this will not be overcome by the CC or
advanced
EGR system though.
Piles
of carbon crust is in the combustion chamber will also increase the
compression engine and can cause hot spots that can increase levels of
NOx. Machines are often detonation will also lead to high concentrations
of NOx.
To help us analyze the condition of the engine, we can use as an aid in the description below:
1.
high CO emissions, showing a condition where too rich AFR (lambda
<1.00). In general, CO showed the efficiency of combustion in the
combustion chamber. The high CO emissions caused by lack of oxygen to
produce a complete and perfect combustion.
Things that cause too rich AFR, among others:
- Idle speed is too low.
- Settings improper carburetor float causing too much gasoline.
- Air filter is dirty.
- Lubricants machine is too dirty or heavily contaminated.
- Charcoal Canister saturated.
- PCV valve that is not working.
- The performance of the fuel delivery system is not normal.
- Air intake temperature sensor is abnormal.
- Coolant temperature sensor is abnormal.
- Catalytic Converter that does not work.
2.
Normal CO. If the AFR is close to or right at the ideal point (AFR 14.7
or lambda = 1.00), the CO emissions will not be more than 1% on the
engines with injection systems or 2.5% on the engines with carburetors.
3.
CO is too low. Actually there is no limit where CO is said to be too
low. The concentration of CO sometimes still visible â € œnormalâ € ??
even though the machine has been working with a very thin mixture.
HC
4.Emisi high. Generally, this condition indicates the presence of
excess unburned gasoline due to the failure of the ignition system or
incomplete combustion. HC concentration measured in ppm (parts per
million). Common causes are not qualified ignition system, a leak in the
intake manifold, and problems in the AFR.
Other causes are:
- Incomplete combustion due to the spark plug is damaged.
- Ignition timing is too backward.
- The cable plugs are damaged.
- Low compression engine.
- Leaks in the intake.
- Error reading data by ECU causing too rich AFR.
5.
Concentration of Oxygen. Indicates the amount of air entering the
combustion chamber is proportional to the amount of gasoline. The ideal
number for oxygen in exhaust emissions ranged from 1% to 2%.
6. The high oxygen concentration. It shows that the AFR is too thin.
Conditions that lead to, among others:
- AFR improper.
- Leaks in the intake tract
- The failure of the ignition system that causes misfire
7. The low oxygen concentration. This condition indicates that the AFR is too rich.
8. elevated CO2 concentration. This condition indicates that the AFR is close to or right in ideal conditions.
9. The low CO2 concentrations. This condition indicates that the AFR is too lean or too rich and leaks in the exhaust system.
10.
The concentration of NOx compounds. NOx compounds including nitric
oxide (NO) or nitric oxide (NO2) is formed when the temperature of the
combustion chamber reaches more than 2500 degrees F (1350 ° C). These
compounds can also be formed when the machine gets heavy loads.
11. The high concentration of NOx.
This indicates:
- EGR Valve does not work.
- AFR too thin.
- Spark Advancer that does not work.
- Thermostatic Water Heater jammed.
- Damage to the cold air duct.
- High crust deposits in the combustion chamber.
- Catalytic Converter abnormal.
12.
The low NOx concentration. Actually there is no restriction that states
too low emissions of NOx compounds. Generally NOx is 0 ppm when the
machine is idle.
