### Conceptual analysis of a four -stroke linear engine [thesis]

Sorin Petreanu
CONCEPTUAL ANALYSIS OF A FOUR-STROKE LINEAR ENGINE By Sorin Petreanu During the past five years at West Virginia University, research into new auxiliary power generation devices has led to the development of a novel crankless reciprocating internal combustion engine. This dissertation presents a conceptual design of a Four-Stroke Linear Engine based on the numerical simulation of the operation of this type of linear engine. The engine consists of four opposed pistons linked by a connecting rod
more » ... y a connecting rod to a linear alternator. A series of numerical simulations was developed and employed to investigate the operation and performance of this crankless, four stroke linear engine. Since this linear engine is crankless, the numerical analysis of this particular engine is a time-based analysis. Two numerical models permit the simulation of the Four-Stroke Linear Engine employing Direct Injection Compression Ignition mode and a Homogeneous Charge Compression Ignition (HCCI) mode. The engine computational model combines dynamic and thermodynamic analyses. A detailed analysis of the engine operation range allows results to be obtained from a parametric study. The parametric study was performed to predict the engine behavior over a wide operating range, given intake parameters, variations in fuel combustion properties, reciprocating mass of the piston shaft assembly, frictional load and the externally applied load, and injection and valve timing. Based on the parametric study a conceptual design for a 15 kW linear engine was developed, showing the effects of reciprocating mass and air to fuel ratio on frequency of operation, power output, and efficiency. The engine analysis shown that this engine has a limited range of operation. The engine operating in as a direct injection compression ignition permitted high efficiency with values between 46 and 49 % corresponding to a compression ratio range between 17 and 35. The analysis performed for the engine operating as a HCCI mode revealed that this particular operating mode depends critically on the start of combustion, which depends in turn on piston motion which is not prescribed. Although the HCCI operation permitted to achieve high values of the efficiency (over 60%) and power output it was observed that the operation domain for the engine was much narrower than for the direct injection case. The results obtained from the numerical simulation show that the FSLE operating under HCCI is difficult to control and this observation extends to any mechanical arrangement of the linear engine with unconstrained piston motion. iii ACKNOWLEDGEMENTS My past five years as graduate student at West Virginia University represent one of the greatest experiences of my life. During this period I had the chance to meet new people and to make a lot of friends. It is very difficult to write this section since there are so many people to mention.