The possibilities for reducing NOx emissions by optimising combustion in the engine alone are limited. In order to comply with the thresholds that are already imposed in particularly sensitive coastal zones, MAN Diesel & Turbo is offering its customers technically sophisticated additional systems. One of these is the humid air motor (HAM) – already tried-and-tested in over 100,000 hours of operation on board ships and in power plants. The technology is available in a slightly different form for both our four-stroke and two-stroke engines. The two-stroke system is called scavenging air moistening (SAM).
 
The principle is as follows: The hot charge air from the compressor is humidified in a water spray chamber. This increases the heat capacity of the charge air on the one hand, allowing it to absorb more heat, while at the same time reducing the oxygen content of the air. The result is a lower combustion temperature in the engine – one of the key factors for NOx content in exhaust gas. HAM technology enables this to be reduced by up to 65 percent. Since untreated seawater can be used to generate the steam, running the HAM system incurs only very minimal additional operating costs.
 
Our sales personnel can also outline further advantages of the humid air motor in customer discussions. The system guarantees high availability with low maintenance. The mist generated in the combustion chamber not only allows clean combustion but also prevents deposits in the chamber, the turbines of the turbocharger and the rest of the exhaust gas apparatus. Nor does our team shy away from mentioning the disadvantages: Using HAM slightly increases the specific fuel consumption and the amount of smoke in the exhaust gas. Use of waste heat is also significantly limited. Other factors to consider are the investment costs and the large area required to house the system.