Surrogate fuels for the simulation of diesel engine combustion of novel biofuels

Abstract

Recently, several promising biomass-derived fuels for diesel engines have been identified, produced, and tested. Diesel engine experiments confirmed very low soot and low nitrogen oxide emissions. With regard to further improvements of the combustion system, it is desirable to complement the diesel engine experiments with numerical simulations. To date, this is hindered by the lack of suitable chemical reaction mechanisms for these novel fuels. Therefore, a surrogate approach is presented here and applied in computational fluid dynamics simulations. Combustion and pollutant formation is simulated using the representative interactive flamelet model. Ignition, combustion, and pollutant formation are described in a consistent manner by inclusion of detailed reaction chemistry. Different mixtures of n-heptane, toluene, ethanol, dimethylether, ethane, and phenol are employed to describe the combustion chemistry of the biofuels. The compositions of the surrogate fuels are compiled according to hydrogen/carbon ratio, oxygen content, cetane rating, and molecular properties of the experimental fuels. Spray, injection, and evaporation properties of the experimental fuels, as obtained from spray vessel experiments, are included in the computational fluid dynamics simulations. By systematic comparison of experimental and numerical results, the surrogate methodology is validated and an improved understanding of the limitations of the current surrogates is achieved. Thus, a methodology for the fast adoption of novel fuels for simulations is proposed that can be used regardless of the availability of specific chemical reaction mechanisms.

Chemical kinetic and combustion characteristics of transportation fuels

“…The methodology of splitting physical and chemical property estimation methods using different representative species for each has been applied frequently but with fewer rigors than above. For example, Kerschgens et al recently used toluene to represent the physical spray properties, and reduced kinetics of a mixtures of n-heptane, iso-octane, toluene, ethanol, dimethyl ether, phenol and ethane to represent the kinetic aspects for simulation of direct injection diesel combustion with 2-methyl tetrahydrofuran, di-n-butyl ether, and their blends as fuel [156]. The purpose of the exercise was to build a platform for rapid initial diesel simulations using new oxygenated alternative fuels.…”

Synthese, motorische Verbrennung, Emissionen: Chemische Aspekte des Kraftstoffdesigns

“…Obwohl, wie zuvor erwähnt, Surrogate für Biokraftstoffe zumeist nicht benötigt werden, kann ihre Definition nützlich sein, wenn chemische Mechanismen für kommende Biokraftstoffe noch nicht verfügbar sind . Allerdings sind solche Surrogatmechanismen dann nicht hinreichend, um feinere Details der Chemie vorherzusagen, wie etwa die Bildung von Schadstoffen.…”

“…Dies ist besonders für neue Biokraftstoffe ein Thema, deren fundamentale Chemie weniger erforscht ist als die von konventionellen Kohlenwasserstoffen. Dennoch hat die Anwendung der chemischen Mechanismen in Motorsimulationen gezeigt, dass diese enorm dabei helfen, ein erstes Verständnis des kraftstoffspezifischen Motorverhaltens zu erlangen, auf dem dann für das Motordesign aufgebaut werden kann.…”

Advanced Biofuels and Beyond: Chemistry Solutions for Propulsion and Production

“…[147] However,s uch surrogate mechanisms will not be sufficient to predict finer details of the chemistry,s uch as pollutant formation.…”

“…With the knowledge obtained in these fundamental studies,m ore realistic mechanisms can be constructed that can be used to model the combustion behavior of the furanic biofuels.H owever, these mechanisms have been validated under conditions that are far from engine applications.T his is particularly an issue for novel biofuels,w hose fundamental chemistry is less explored than that of conventional hydrocarbon fuels.H owever,t he application of such chemical mechanisms in engine simulations [147] has shown that these are tremendously helpful to gain an understanding of fuel-specific engine behavior, which can then be used in engine design. Figure 11.…”