Computer-Aided Simulation of the Volumetric Efficiency of a 2 MW Gas Engine

In a mean value thermodynamic model of an internal combustion engine, operational parameters such as volumetric efficiency have a significant effect on the thermal performance of the engine, for example the combustion process inside the cylinder depends on the air-fuel ratio, large amounts of air are introduced to the combustion chamber require and consequently more fuel it is needed, which traduces in a higher output engine torque and electrical power. The air-fuel flow in the admission line has an appreciable inertia due to the turbocharged operation, but the intake manifold, the admission valves and the throttle act as an obstruction for the air-natural gas. Considering everything considered before, this paper proposes a model for the volumetric efficiency on the 2 MW Jenbacher Gas Engine, which is the capacity of the engine to fill the available geometric volume of the engine with a new charge of the air-fuel mix. A thermodynamic model was introduced to study the ratio between the real volume of air drawn off the cylinder, concerning the theoretical geometric volume of the cylinder based on a typical day of operation of the thermal power plant. Finally, to show the impact of the volumetric efficiency on the model results, a regression as a function of the intake manifold temperature and pressure, the volumetric gas flow and the engine revolutions was proposed. This allows to estimate the engine volumetric efficiency with a quadratic accumulated error ranging from 5.65 (when the volumetric efficiency model depends only on the air-gas mixture pressure) to 1.94 (when the model was correlated as a function of the pressure and temperature of the inlet manifold, motor angular speed, and the volumetric natural gas flow). The study gives evidence about a successful simulation of a Natural Gas Engine thermodynamic model built in Matlab due to the similarity found between the simulated results and the experimental data obtained fromt the data acquisition software installed on the equipment, obtaining in most cases a good accuracy to predict the effective efficiency and the electric power under different operation conditions.