Neutralization of exhaust gases (Mondeo 3)

Example Duratec-HR: two lambda sensors in carburettor engines

1 — Pre-activated lambda sensor, 2 - After-activated lambda sensor,	3 - Catalyst, 4 - Additional noise muffler.

Chemically renders up to 90% of exhaust gas components harmless: three-way catalytic converter

1 of 2 CO 2 O ₂ is CO ₂; from 2C ₂ H₆ 7О ₂ became 4СО ₂ 6 Н ₂ О; from 2NO 2CO we get N ₂ CO ₂.

1 — Lambda sensor, 2 - Ceramic monolith, 3 - Elastic metal weave,	4 - Heat-containing double bowls, 5 - Platinum-rhodium coating, 6 - Ceramic or metal supporting body.

Fuel is mainly made up of components such as carbon and hydrogen. When burned in an engine, carbon combines with oxygen from the air to form carbon dioxide (CO 2), and hydrogen (H) with the same oxygen (O 2) creates water (H 2 O). About 0.9 liters of water are formed from one liter of fuel. It is removed as "invisible" water vapor from the exhaust system. However, in winter, when starting a cold engine, white exhaust clouds can often be observed - an indirect sign of condensed water.

Mondeo with catalytic converter – diesel with oxidation catalyst – all Mondeo with EGR

All petrol-powered Mondeos are now equipped with a single regulating catalytic converter, including exhaust gas recirculation. In contrast, diesel variants have a single oxidation catalytic converter and an exhaust gas recirculation system. The regulating catalytic converter reduces carbon monoxide by around 85%, hydrocarbons by 80% and nitrogen oxides by almost 70%. The oxidation catalytic converter leaves nitrogen oxides alone (the recirculation system takes care of this). The designation "regulated" indicates that the exhaust gas emissions, unlike those with an oxidation catalytic converter, are actively measured during operation and adjusted within the prescribed minimum. However, as the distance travelled (mileage) increases, each catalytic converter loses its "influence".

Measures the oxygen content in the exhaust gas - lambda sensor

In order to reduce the reaction time of the "poisonous lard", an oxygen sensor is installed in the Mondeo directly in the exhaust manifold and behind the catalytic converter. It continuously analyzes the residual oxygen content in the exhaust gas. It sends its "information" to the electronic control unit: depending on the current measurements, the on-board computer sets the composition of the air-fuel mixture (lean, rich). This is done in a rapidly changing sequence. Excess air for combustion of hydrocarbons, insufficient air to reduce nitrogen oxides. The "regulated" exhaust gases pass through the catalytic converter, which - as already mentioned - converts them into carbon dioxide, water vapor and nitrogen.

Catalyst operating temperatures

In order for the catalytic converter and the lambda sensor to function, their operating temperatures must be reached (catalytic converter: about 300°C). This work is performed by the hot exhaust gas for 25–80 seconds. However, these two elements react very sensitively to excessive heating. For example, when unburned residues of the combustible mixture ignite in the hot catalytic converter (misfiring), the temperatures inside can rise to dangerous values. A constant temperature of around 1200°C can prematurely age the catalytic converter; at temperatures above 1400°C, the ceramic housing melts and the lambda sensor becomes too hot. A melted catalytic converter can be "exposed" with "good ears" by hissing exhaust noises – this is caused by increased exhaust back pressure – and a sharp loss of power. Get to work on finding out the reasons right away, otherwise the new catalytic converter under your Mondeo will have a short life, and the exhaust valves in the cylinder head will burn out in a very short time.

Pay attention to misfiring: especially when shifting from high gears or driving down mountain roads in forced idle mode - if sounds are heard from the exhaust system, thoroughly get to the bottom of the cause of this phenomenon.

PRACTICAL ADVICE

Handling the catalytic converter If your Mondeo has problems starting – usually due to a flat battery – do not drive, move or tow the car. This can cause a lot of unburned fuel to get into the catalytic converter and cause it to fail. Ignition failure or misfires indicate faults in the ignition system. It is necessary to quickly establish the cause or call a specialist with measuring equipment to your Mondeo. Before installing the new underbody protection, "pack" the catalytic converter well, otherwise it is at immediate risk of fire. Occasionally also check the heat shield above the catalytic converter for damage. A leaky exhaust system (burnt gaskets, temperature cracks, rust defects, etc.) before the lambda sensor distorts the measurement results (increased oxygen content). The electronic engine control unit therefore gives a command to enrich the mixture. An error in the electronic unit causes increased fuel consumption and premature aging of the catalyst.

Information for this article was taken from the website FordBook.ru