Numerical Investigations of the Auto-Ignition Ranges of a Natural Gas Fueled HCCI Engine 2017-32-0073
Homogeneous charge compression ignition (HCCI) in natural gas fueled engines is thought to achieve high efficiency and low NOx emissions. While automotive applications require various load and speed regions, the operation range of stationary cogeneration engines is narrower. Hence, HCCI operation is easier to reach and more applicable to comply with future emission standards.
This study presents computationally investigations of the auto-ignition ranges of a stationary natural gas HCCI engine. Starting from a detailed 1D engine cycle simulation model, a reduced engine model was developed and coupled to chemical kinetics using AVL Boost. Compression ratio, air-fuel ratio, internal EGR rate (iEGR) and intake temperature were varied for three different speeds, namely 1200, 1700 and 2200 rpm. Each examination includes a full factorial design study of 375 configurations.
In the first step, the combustion was calculated using the GRI-mechanism 3.0 and a single zone combustion model. The data generated was analyzed and single effects of the design parameters on auto-ignition characteristics were derived. In the second step, quadratic regression models were built and sensitivity analysis was performed. Compression ratio and intake temperature show the largest impact on auto-ignition timing (AIT) and auto-ignition temperature, whereas iEGR and air-fuel ratio mainly influence indicated mean effective pressure (IMEP). The design space indicates narrower auto-ignition range at lower engine speed due to decreasing volumetric efficiency and increasing heat losses.
