EFFECT OF SWIRL MOTION ON THE COMBUSTION IN A BIOGAS-DRIVEN INTERNAL COMBUSTION ENGINE AT PARTIAL LOAD OPERATION

In this study the combustion characteristics of a fully integrated biogas cogeneration unit of 150 kW is examined with respect to flow and swirl numbers of different cylinder head designs also regarding different loads. Two cylinder heads were characterized by its flow numbers on a flow bench and then used on the motor. Combustion velocity was analyzed at loads of 50%, 75%, and 100%. Analysis of heat release and cylinder pressure was done using full motor indication. All tests were done meeting the mandatory NOx 500 mg/m(3) regulations. The characterization of the cylinder heads by flow and swirl numbers was done on a static flow bench at MCI. An integrative methodology for determining the swirl numbers was applied. With this method flow and swirl numbers were derived from torque meter and mass flow measurements at varying valve lifts. The used cylinder heads both have identical inlet ports and a bore diameter of 130 mm. The cylinder heads differ in their valve seat geometry. The new valve seat design proves to have significant influence on the swirl motion generated by the inlet port. A higher swirl also means a reduced overall flow rate. Motor performance was evaluated by its heat release over crank angle (CA). Faster heat release and higher burning velocity was achieved with the new seat design. Comparing crank angle at 50% mass fraction burned a higher swirl makes for an earlier burning focus. Considering flow characteristics with respect to cylinder pressure and heat release at full load, the flow optimized valve seats of the cylinder head generate an increased heat release parallel to higher cylinder pressure at all load conditions.