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Hydrogen-diesel dual fuel (HDDF) technology is one approach available to improve the performance and reduce carbon-based emissions of compression ignition (CI) engines. Unfortunately, when operated at partial and low loads, HDDF engine configurations suffer from poor fuel utilization, combustion efficiency and ignition delay. As partial load application is increasingly important to performance of hybrid power systems, this paper explores the use of oxygen enrichment to improve HDDF performance outside of conventional load applications. In this paper, a numerical model was first developed and validated for HDDF combustion using experimental data. This model was subsequently applied to study the influences of oxygen enrichment on engine performance and emission characteristics. Furthermore, the Exhaust Gas Recirculation (EGR) was implemented as a secondary control for NOx emission reduction. For this configuration the results showed that oxygen enrichment (between 21% and 27% by volume) into the intake manifold led to an improved combustion efficiency and reduced carbon-based emissions. The brake thermal efficiency (BTE) increased by 1.6% and the brake specific energy consumption decreased by 4%. Across the emissions spectrum, soot emission reduced by 72%, whereas NOx emission increased by 63% without using the EGR technique. By combining oxygen enrichment and EGR strategies, a considerable reduction of 79% in NOx and an increase of 2.6% in BTE was observed for the oxygen concentration of 27% and EGR rate of 24% compared to a conventional HDDF operation with 45% HES ratio. [Display omitted] • Effect of oxygen enrichment on hydrogen dual-fuel engine performance was studied. • Thermal efficiency of dual-fuel engines was improved by oxygen enrichment. • Oxygen enrichment reduced carbon-based emissions and increased NOx emissions. • EGR significantly reduced NOx emissions and slightly increased system efficiency. • Combined EGR and oxygen enrichment techniques largely improved engine performance. [ABSTRACT FROM AUTHOR]

Consumers conventionally adopt diesel generation to meet the energy needs where the grid connection is unreliable or unavailable. While electrification has provided these communities a variety of economic and social opportunities, diesel consumption has resulted in adverse costs and environmental pollution. Two technologies available to reduce the expense and emissions of diesel fuel reliance include dual fuel or hybrid diesel applications. The dual-fuel approach involves a supplementary gas fuel charge in support of reduced diesel fuel consumption. Hybrid applications involve the integration of renewable generation to displace diesel fuel consumption. This paper reviews the potential for hybrid dual-fuel applications, identifying engine flexibility as a major integration barrier. In comparing the flexibility of various dual-fuel technologies to operate dynamically, this paper presents a critical review across hydrogen, liquified petroleum gas (LPG), natural gas (NG) and blended hydrogen and NG derivatives. The results identify a range of approaches able to improve engine flexibility and thus reduce the cost and carbon intensity of diesel-fired internal combustion engines. At low load conditions, while NG and LPG exhibit similar performance, the use of hydrogen and hydrogen blends provide improved engine performance and response. Unfortunately, given the current cost of hydrogen fuel, significant commercial barriers exist to the adoption of hydrogen or hydrogen blended fuels. Despite this, this review indicates the potential of hydrogen-NG blends to offer additional flexibility in comparison to alternative dual-fuel technologies. This position is furthered considering near term cost targets associated with the development of a global green hydrogen industry, coupled with its ability to serve as a demand-side management approach within isolated power systems, one of the multiple future research themes. • The potential of dual fuel approach in renewable energy applications was assessed. • Different dual fuel technologies were compared over various conditions. • Dual fuel low load application was discussed to manage the variability of RE sources. • The ability of H 2 , NG and LPG dual fuel approaches operate at low load was compared. • EGR and Fuel Injection were effective methods to improve combustion performance. [ABSTRACT FROM AUTHOR]

We give counterexamples to a result in F. Esser and F. Harary [2, Theorem 3] asserting that two nonisomorphic complete r -partite graphs with the same number of vertices have different spectral radii. We then derive some results on invariant factors and apply them to obtain relationship between the parameters of integral complete multipartite graphs and their integer eigenvalues. Necessary conditions for complete multipartite graphs to be integral are obtained. [ABSTRACT FROM AUTHOR]

Diffusivity equation which can provide us with the pressure distribution, is a Partial Differential Equation (PDE) describing fluid flow in porous media. The quadratic pressure gradient term in the diffusivity equation is nearly neglected in hydrology and petroleum engineering problems such as well test analysis. When a compressible liquid is injected into a well at high pressure gradient or when the reservoir possess a small permeability value, the effect of ignoring this term increases. In such cases, neglecting this parameter can result in high errors. Previous models basically focused on numerical and semi-analytical methods for semi-infinite domain. To the best of our knowledge, no analytical solution has yet been developed to consider the quadratic terms in diffusivity PDE of one-dimensional unsteady state fluid flow in rectangular coordinates and finite length. Due to the resulting errors, the nonlinear quadratic term should also be considered in the governing equations of fluid flow in porous media. In this study, the Fourier transform is used to model the one-dimensional fluid flow through porous media by considering the quadratic terms. Based on this assumption, a new analytical solution is presented for the nonlinear diffusivity equation. Moreover, the results of linear and nonlinear diffusivity equations are compared considering the quadratic term. Finally, a sensitivity analysis is conducted on the affecting parameters to ensure the validity of the proposed new solution. The results demonstrate that this nonlinear PDE is also applicable for hydraulic fractured wells, and well test analysis of fractured reservoirs. [ABSTRACT FROM AUTHOR]