GT-Power Modeling of a 6-Cylinder Natural Gas E>ngine and Investigation of the Possible Performance Improvements by Studying the Miller Cycle

Sammanfattning: This master thesis has been conducted at the Division of Combustion Engines under the Department of Energy Sciences, Faculty of Engineering at the Lund University. The purpose of this master thesis project is to create a computer based model of a Natural Gas Engine in order to raise its potential for updating a Volvo bus as well as creating a study of the improvement efficiency of the Miller Cycle. In the last 100 years, there has been enormous progress in the internal combustion engine field. The emission of reactive Hydrocarbon from light duty vehicles is approximately. 70 percent lower in natural gas operation than with petrol operation. Emissions of greenhouse gases are 15-25 percent lower with in natural gas operation than from corresponding petrol vehicles. Environmental improvement by reducing emissions as well as alternative energy issues will become more and more important in the future. Diesel engines have a higher efficiency level compared to gasoline engines, but the problem is that their NOx and Soot emissions are higher than other types of engines. That’s one of the main reasons why Natural Gas engines became more and more important over the last few years. New gas buses that are run with vehicle gas emit approximately 50% less NOx than corresponding diesel buses, something that can to contribute substantially to creating better air environment in the big towns. Moreover, the emission is reduced of carcinogenic pollutants and particles. [1] The gas engine project at Lund University is exploring the extension of the performance, fuel efficiency and the stability of a spark ignition (SI) natural gas engine. The engine is a partly modified (modified from a single point to multi-port injection system), 6-cylinder turbocharged (9.4 liter) Volvo engine, which is equipped with EGR valves and an EGR cooler. The engine runs on a Stoichiometric mixture of air and fuel associated with the cost effective 3-way after treatment system. The work presented in this thesis has focused on studying, with simulation, an engine model for new gas buses that is run with natural gas and a study with Miller Cycle. This research has been conducted in a 1-D gas exchange simulation program called GT-Power with an engine model originating from VOLVO. As well, during the verification of this model, testing cases were modified to produce different tests.