Assessing the Influence of Compression Ratio on Engine Characteristics Including Operational Limits of a Biogas-Fueled Spark-Ignition Engine

Abstract

Biogas, which is a renewable alternative fuel, has high anti-knocking properties with the potential to substitute fossil fuels in internal combustion engines. In the present study, performance characteristics of a spark-ignition engine operated under methane (baseline case) and biogas are compared at the compression ratio (CR) of 8.5:1. Subsequently, the effect of CR on operational limits, performance, combustion and emission characteristics of the engine fueled with biogas is evaluated. A variable compression ratio, spark-ignition engine was operated at various CRs of 8.5:1, 10:1, 11:1, 13:1 and 15:1 over a wide range of operating loads at 1500 rpm. Results showed that the operating range of the engine at 8.5:1 CR reduced when biogas was utilized in the engine instead of methane. However, the operating range of the engine for biogas extended with an increase in CR - an increase from 9.6 N-m-16.5 N-m to 2.8 N-m-15.1 N-m was observed when CR was increased from 8.5:1 to 15:1. The brake thermal efficiency improved from 13.7% to 16.3% and the coefficient of variation of indicated mean effective pressure reduced from 12.7% to 1.52% when CR was increased from 8.5:1 to 15:1 at 8 N-m load. The emission level of carbon dioxide was decreased with an increase in CR due to an improvement in the thermal efficiency and the combustion process.

Experimental analysis of the system behavior of a two-stage variable compression ratio (VCR) system in fired SI-engine operation

“…4–7 Furthermore it is also an effective method to improve the performance and operating range of dual fuel engines, for example, with bio gas or hydrogen. 8,9…”

“…[4][5][6][7] Furthermore it is also an effective method to improve the performance and operating range of dual fuel engines, for example, with bio gas or hydrogen. 8,9 The mechanical implementation of VCR systems that allow to adapt the Top Dead Center (TDC) position of the piston can be classified into three major groups: 10 (1) An additional pivot or supporting point of the conrod due to unconventional cranktrain components, for example, multi-component conrods or racks gearboxes. [11][12][13] (2) An adjustable distance between cylinder head and the crankshaft, for example by using eccentric main bearings or tilting mechanisms of the cylinder head.…”

“…In addition to the mechanical coupling, they are also hydraulically interconnected by the 5/2-way valve (9). Both support chambers are connected to the conrod bearing oil supply via Check Valves (CV) (7) + (8). The hydraulic connection of the support chambers can be designed in different ways.…”