Exhaust System, Basic Function - GF49.00-P-1001A

Engine All (4xWD) 

Engine All (CAR) 

Courtesy of MERCEDES-BENZ USA

Sample illustration of exhaust system 

Overview 

This document contains information on:

• General 
• Function 
  • On diesel engines 
  • For spark-ignition engines 

General 

The exhaust system is part of the engine management and fulfills the tasks involved in exhaust gas cleaning:

• Exhaust routing away from the vehicle
• Cleaning of exhaust gas to reduce pollutants
• Recirculating exhaust gas for preventive pollutant reduction
• Reduction of exhaust noise

Function 

The purpose of the exhaust manifold in the exhaust system is to guide the exhaust gas out of the cylinder exhaust ports and into the exhaust system. The construction affects the engine output, the exhaust gas temperature and the acoustics of the exhaust system. Air gap insulation allows the exhaust manifold to contribute to increasing the exhaust gas temperature, which increases the efficiency of the catalytic converters. The exhaust manifold is produced from heat resistant material to protect against high temperatures, e. g. high-alloyed stainless steel or alloyed cast iron.

Catalytic converters and soot particulate filters (6, 16) form the components for the exhaust gas cleaning. They clean and filter the pollutants that are hazardous to health and the environment which are generated during fuel combustion. This includes the following pollutants:

• Nitrogen oxides (NO_x )
• Hydrocarbons (HC)
• Carbon monoxide (CO)
• Soot particles

Catalytic converters ensure that these pollutants are reduced through the chemical catalytic process. As the pollutants vary depending on the fuel type, different types of catalytic converters are used in diesel and spark-ignition engines. The catalytic converters are installed near the engine. This way, they reach their operating temperature quickly and start working early on, even after a cold start. In the three-way catalytic converter (3), the operating temperature lies at 300°C, for example.

Courtesy of MERCEDES-BENZ USA

Sample diagram of exhaust system, shown on engine 654 

The following catalytic converters are used in exhaust systems, depending on the fuel type:

For diesel engines: 

• Oxidation catalytic converter (14)
• SCR catalytic converter (in modular unit with soot particulate filter) (16)

For spark-ignition engines: 

• Three-way catalytic converter (3)

A soot particulate filter (6, 16) ensures that the soot particles are filtered and oxidized. It is also installed near the engine. As a result of the higher exhaust gas temperature, the retained soot particles can burn off better during the regeneration phase. Diesel engines rarely reach sufficiently high exhaust gas temperatures to burn off soot particles. For this reason, an oxidation catalytic converter (14) is installed upstream in diesel exhaust systems. It ensures a chemical breakdown of collected soot particles at low exhaust gas temperatures. The soot particulate filter (in modular unit with SCR catalytic converter) (16) in diesel engines is made from silicon carbide, while the soot particulate filter (6) in spark-ignition engines is made from the more heat resistant cordierite.

Depending on the fuel, an optimization, monitoring and regulation of the pollutant reduction is realized by means of corresponding temperature sensors (5, 19), lambda sensors (1, 2) and NOx sensors (12, 17). Spark-ignition engines are partially equipped with soot particulate filters (6) without regulating temperature sensors (5). These soot particulate filters (6) have a high filtration efficiency, are maintenance-free and self-regulating. Lambda sensors (1, 2) measure the residual oxygen content in the exhaust gas and are used in spark-ignition engines. NO_x sensors (12, 17) determine the nitrogen oxide and oxygen concentration in the exhaust gas as well as the ammonia concentration downstream of the SCR catalytic converters (in modular unit with soot particulate filter) (16).

Due to its exhaust gas recirculation function, the exhaust system is passively involved in the charge exchange. The design of the exhaust system affects the outflow behavior of the exhaust gas and thus indirectly affects the fresh air supply.

	Additional basic functions
	Exhaust gas flap controller, basic function	Engine all (CAR)	GF49.10-P-2005A
	Soot particulate sensor, basic function	Engine 608 in model 118, 177, 247 with code 460 (Canada version) with code 494 (US version) Engine 654 in model 118, 167, 177, 206, 247 with code 460 (Canada version) with code 494 (US version) Engine 654 in model 213, 238, 257 as of model year 2021 with code 460 (Canada version) with code 494 (US version) Engine 656 in model 167, 223 with code 460 (Canada version) with code 494 (US version) Engine 656 in model 213, 238, 257 as of model year 2021 with code 460 (Canada version) with code 494 (US version)	GF49.20-P-2004A
	Exhaust system temperature sensor, basic function		GF49.20-P-2005A