Today the environmental issues are a lot on the agenda and the environmental awareness are more and more common. New laws and restrictions on engines emissions are enforced and the demand on the engines gets higher and tougher. This leads to the engine testing playing a more crucial part than ever. Engine tests are done using an engine dynamometer. The dynamometer loads the engine by, in many different ways, absorbing the power and torque generated by engine. The most important functions of a dyno are to convey the power from the engine to the dyno, to load the engine, to measure the power and torque generated by the engine and to remove the excess heat that is generated.  Husqvarna is a Swedish company that produces garden and forest cutting tools, their most famous products are their chainsaws. Husqvarna does an extensive amount of engine testing, long time testing, functional testing and field testing. Some functional tests, such as start-ability after use is done in a climate chamber where the humidity and temperature can be set. Today, loading a chainsaw in -25 °C is a problem due to the fact that the most used dynamometer at Husqvarna is a water brake that freezes in minus degrees. This master thesis will answer the question on how to, for small engine, simulate the load that occurs during normal use of the engine and how to develop a dynamometer suitable for Husqvarna’s needs? The focus when developing the dynamometer will lie on solving the problem with minus degrees and having a good detachable coupling between the dyno and the chainsaw. The result is a hydraulic oil dynamometer. A hydraulic pump is attached to the guide bar and chainsaw using a detachable key way coupling and bearings. By controlling restriction of the flow in the hydraulic system the load can be controlled and also ultimately the RPM of the chainsaw. The hydraulic oil works fine in the minus degree as long as the right oil with the right viscosity range is used although a problem with the small chainsaws are that they are not reaching the full RPM in -25 °C. Mainly because of the backpressure created by the components in the system. This can be solved by minimizing the hydraulic systems total flow restriction.   However this problem doesn’t affect the testing methods as long as the chainsaw easily can be disconnected and freed from the dynamometer and then be run to full RPM which the coupling between the pump and chainsaw enables.

Growing concerns about interruption to oil supply and oil shortages have led to escalating global oil prices. In addition, increased public acceptance of the global warming problem has prompted car manufacturers to agree to carbon emission targets in many regions including most recently, the Californian standards. Other legislating bodies are sure to follow this lead with increasingly stringent targets. As a result of these issues, spark ignition engines in their current form will need significant improvements to meet future requirements. One technically feasible option is smaller capacity downsized engines with enhanced power that could be used in the near term to reduce both carbon emissions and fuel consumption in passenger vehicles.This research focuses on exploring the performance limits of a 0.43 liter spark ignited engine and defining its operating boundaries. Limiting factors such as combustion, gas exchange and component design are investigated to determine if they restrict small engine performance. The research gives direction to the development of smaller gasoline engines and establishes the extent to which they can contribute to future powertrain fuel consumption reduction whilst maintaining engine power at European intermediate class requirements.