Diesel/biodiesel/biogas mixtures driven compression ignition internal combustion engines constructal design

Abstract

This paper introduces a first and second law based transient mathematical model for 4-stroke compression ignition internal combustion engines (CI-ICE) driven by diesel/biodiesel/biogas mixtures to allow for the maximization of system performance. In this way, the CI-ICE morphology that provides easier access to the currents that flow through it is sought, according to constructal law. The total entropy generated in the CI-ICE cycle was calculated by adding the entropy generation in all strokes. An optimization problem was formulated based on the variation of operating and geometric parameters, and the objective functions were the effective and 2nd law efficiencies, ηef and ηII, as well as the destroyed exergy fraction, yD. The optimal ranges found for the bore-stroke, compression and conrod-crank ratios were 0.51≤Bopt≤1.25; 2.07≤ROD/CSopt≤4.14, and 10.23≤CRopt≤33.44 in which ηefηIImax≃0.330.37 with yD,min≃0.66 for D100 (pure diesel), and ηefηIImax≃0.310.35 with yD,min≃0.64 for B50D25NG25 (biodiesel/diesel/natural gas blend). The maxima and minimum found were sharp, since ηef and ηII varied up to 71% and 69% in comparison to their maximum values, respectively, and yD up to 45% in comparison to its minimum value within the adopted ranges of variation of the optimized parameters. Such large variations stress the importance of considering the optimized CI-ICE morphology in actual design, i.e., CI-ICE constructal design.