THC emissions from gas engines

Owing to their high efficiency and lower NOx and soot emissions, gas engines are frequently used in decentralised energy supply systems. However, they can emit high amounts of unburned hydrocarbons (THC – Total Hydro Carbon). The project has set itself the goal of identifying engine-related measures for optimised combustion and thus minimise THC emissions. Comprehensive experimental tests were conducted using a single-cylinder research engine and an optical engine. These served to verify the newly developed simulation model with which the THC content can be reliably pre-determined. The level of THC emissions depends especially on the air-fuel ratio. When all relevant parameters are optimally aligned, these emissions can be dramatically reduced and the effectiveness further increased. However, the higher resulting NOx values must be compensated for using an effective exhaust gas treatment.

» The project results enable us to develop new strategies for minimising emissions and thus to optimise the total system effectively. «
Dr. Ulf Waldenmaier (MAN Diesel & Turbo SE)


Efficient gas engines play a huge role in decentralised energy supply systems. Compared to other thermal generating technology, they score well because of their lower CO2 as well as soot emissions and NOx emissions. The higher share of THC in the exhaust gas of gas engines is, however, an issue. To minimise these greenhouse gases from even emerging, engine-related measures for combustion optimisation are pursued. This project focuses on analysing these measures.


Using a single-cylinder research engine, the influences of different combustion parameters were investigated experimentally. The theoretical work concentrated on modelling how THC emissions emerge. The model is based on a hybrid approach that considers reaction-kinetic approaches as well as airflow and combustion. An optical engine, on which the flame spread of different ignition systems and timing was tested, was used for calibrating the combustion model. On the basis of practical and simulative results, an evaluation mix was developed that can be used for assessing the effectiveness of THC reduction possibilities.


The newly developed simulation model qualifies as a tool for engine optimisation because it can pre-determine experimental values with satisfying accuracy. It has been shown that the air-fuel ratio has the largest impact on the emergence of THC emissions. Further important influencing factors are the wall temperature, crevice volume, timing, ignition system and carburetion. Optimally aligning these parameters leads to considerably lower THC emissions. The project results suggest that a rethinking of new emission concepts should be considered. If minimising THC is the focus of engine-related emissions, higher NOx levels post-combustion go hand-in-hand with greater engine efficiency. In this case, NOx reduction must concentrate fully on post-treatment with catalysers.


THC emission gas engines | Formation principles and reduction of THC emissions from gas engines | Project No. 1127



Public & FVV Funding

640.000,00 EUR

Time Period
2012-11-01 to 2015-10-31

Research Association for Combustion Engines (FVV) eV

Lyoner Strasse 18
60528 Frankfurt am Main

Specialist Agency Renewable Raw Materials (FNR) eV

Hofplatz 1
18276 Gülzow-Prüzen


Dr. Ulf Waldenmaier
MAN Diesel & Turbo SE

RTD Performers

1 | Institute of Internal Combustion Engines (LVK), Department of Mechanical Engineering - Technical University of Munich (TUM)

Head of research:
Prof. Dr.-Ing. Georg Wachtmeister

2 | Institute of Combustion Technology (ITV) - Leibniz Universität Hannover

Head of research:
Prof. Dr. Friedrich Dinkelacker

Technical University of Munich (TUM)

Institute of Internal Combustion Engines (LVK)

Arcisstrasse 21
80333 Garching

Leibniz University Hannover

Institute for Combustion Technology

Welfengarten 1A
30167 Hanover

Project Management

Ralf Thee

+49 (0) 69 6603 1349
+49 (0) 69 6603 2349

Research Association for Combustion Engines eV

Lyoner Strasse 18
60528 Frankfurt am Main
T +49 69 6603 1345