Numerical Simulation of a Prechamber-Ignited Lean-Burn Gas Engine by Means of Predictive Combustion Models
Abstract:
In the recent period, lean-burn gas operation has been gaining large attention
both in the marine sector and for power generation since it allows to achieve
very low Nitrogen Oxides (NOx) emissions and to reduce carbon footprint compared
to conventional diesel engines. However, to ensure a stable and efficient
combustion process, innovative ignition systems able to deliver high energy
content have to be considered. The employment of an active Pre-Combustion
Chamber (PCC) ignition system is nowadays considered one of the most effective
solutions for large-bore gas engines.
In active PCC engines, the lean gas mixture in the Main Chamber (MC) is ignited
by hot jets flowing from the PCC, resulting from a near-stoichiometric gas
spark-assisted combustion in the PCC. The ability to describe and model both the
PCC and MC combustion process with (zero-dimensional/one-dimensional) 0D/1D
models has gained great importance in the last years since it could enable the
exploitation of predictive simulation tools as a support to testing activities
in the engine development phase.
In this regard, in this activity a simulation methodology for a PCC gas engine is
presented. Two combustion models, one for the PCC and the other for the MC
phenomena, were investigated for the combustion process simulation. Experimental
measurements from a six-cylinders Wärtsilä engine were used to assess the
predictive capabilities of the numerical model, considering several engine
operating conditions and engine calibrations. Moreover, three different PCC
systems were investigated in this study to evaluate the model accuracy also
considering different PCC shapes and geometry features. The investigated
combustion models showed great accuracy in simulating the ignition process and
combustion behavior of the analyzed engine.