The objective of the work presented in this paper is to contribute to the development of CHP systems based on conventional diesel engines but fuelled with pyrolysis oil or pyrolysis oil derived fuels. Experiments have been carried out using a one-cylinder, 20 kW(e) diesel engine, which was adapted to enable the feeding of different fuels and the monitoring of its performance. Apart from the introduction of a completely new stainless steel fuel injection system also specific measures have been implemented to overcome the difficult and slow ignition behavior of pyrolysis oil. Pyrolysis oil could be successfully combusted provided the air inlet temperature was increased to 100-120 degrees C at an engine compression ratio of 17.6. This temperature can be reduced by approximately 40 degrees C when the compression ratio is increased to 22.4. Generally, pyrolysis oil fuelling led to an increase in CO emission and a decrease in NOx emission. Apparently, peak temperatures in the cylinder are lower upon fuelling pyrolysis oil. A 'duration' experiment of 40 h was carried out while fuelling pyrolysis oil, without any notable effect on flue gas emissions and fuel consumption. This is considered as a very promising result, but further long-term testing will be required. (C) 2012 Elsevier Ltd. All rights reserved.