Hakan Serhad Soyhan

Numerical investigation of the stability of bubble train flow in a square minichannel

The stability of a train of equally sized and variably spaced gas bubbles that move within a continuous wetting liquid phase through a straight square minichannel is investigated numerically by a volume-of-fluid method. The flow is laminar and cocurrent upward and driven by a pressure gradient and buoyancy. The simulations start from fluid at rest with two identical bubbles placed on the axis of the computational domain, the size of the bubbles being comparable to that of the channel. In vertical direction, periodic boundary conditions are used. These result in two liquid slugs of variable length, depending on the initial bubble-to-bubble distance. The time evolution of the length of both liquid slugs during the simulation indicates if the bubble train flow is “stable” (equal terminal length of both liquid slugs) or “unstable” (contact of both bubbles). Several cases are considered, which differ with respect to bubble size, domain size, initial bubble shape, and separation. All cases lead to axisymmetric ...

An Experimental and Modeling Study to Investigate Effects of Two-Stage Direct Injection Variations on HCCI Combustion

In this study, homogenous charge compression ignition (HCCI) combustion with two-stage direct injection (TSDI) strategies was modeled with stochastic reactor model (SRM) and validated by using the experimental results of the TSDI gasoline HCCI engine. For the experimental study, a diesel engine was converted to an electronically controlled HCCI gasoline engine. The effects of injection timings and injection ratios on the HCCI combustion characteristics were studied at high equivalence ratio and constant engine speed. The injection timings (first and second) and fuel quantity for each injection were adjusted to get desired mixture formation in the cylinder. During the experiments, the maximum cylinder gas pressure, pressure rise rate and start of combustion were directly controlled by using the second fuel injection timing and injection ratio. Using optimal second fuel injection timing and injection ratio caused a reduction on NOx and HC emissions. The model results of the HCCI combustion were in good agreement with the experimental results. Both of the experimental and modeling results showed that the second fuel injection timing had a strong effect on the HCCI combustion when compared to the first injection timing.

Investigation of performance of 0-D internal combustion engine simulation codes based on detailed and reduced chemical kinetic mechanisms

In this study, combustion performance of two 0-D engine simulation codes, Chemkin-Pro and SRM Suite, was examined in a homogenous charged compression ignition (HCCI) engine and comparisons were made against the experimental data, which was based on combustion of TRF-70 (70% toluene and 30% n-heptane in vol. basis). Reduced and semi-detailed chemical kinetic mechanisms of TRF-70 were used in both codes for performance evaluations in terms of pressure, heat release rate and exhaust gas emissions (CO, CO2 and O2). OH and H2O2 emissions, which were difficult to obtain experimentally, were compared computationally among codes using both semi-detailed and reduced mechanisms. Both codes had advantages over the other; stochastic reactor model (SRM) resulted in better results than Chemkin-Pro in terms of pressure and heat release rate when compared to experimental data, while Chemkin-Pro was advantageous owing to its shorter CPU time with acceptable proximity to experimental data.

Recent Trends in Internal Combustion Engines

This special issue is devoted to the recent trends in internal combustion engines. Recent trends in internal combustion engines aim to reduce fuel consumption and also lower exhaust gas emissions.The aim of this special issue is to bring all topics and all the scientific/technological approaches in recent trends in internal combustion engines. We, as editorial team, received several contributions as original research articles and review articles that will stimulate the continuing efforts to understand new technologies in internal combustion engines (ICEs). The papers are “Design and implementation of the control system of an internal combustion engine test unit” by T. Koc et al., “Trends of syngas as a fuel in internal combustion engines” by F. Y. Hagos et al., “Simulation analysis of combustion parameters and emission characteristics of CNG fueled HCCI engine” by P. M. Diaz et al., “Calibration and validation of a mean value model for turbocharged diesel engine” by R. Li et al., “Fuzzy sets method of reliability prediction and its application to a turbocharger of diesel engines” by Y.-F. Li and H.-Z. Huang.

Performance of a direct diesel engine using aviation fuels blended with biodiesel

In this study, jet fuel (JF) and railroad fuel (D2) with SME blends (5%, 20%, 50%) were used in a four-cylinder, naturally aspirated, direct (DI) diesel engine. The engine was operated under full load and tested at various speeds to determine the engine’s performance and exhaust emission characteristics. The experimental results show that as the SME ratio of the fuels increases, the break specific fuel consumption (BSFC) and exhaust temperature increase; the SME and its blends show a slight drop in engine performance. In this experiment, carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx) and smoke opacity values were measured for each fuel. The results of the emission tests revealed that the oxygen content of SME provided a significant reduction in CO and smoke opacity emissions. However, when the test engine was fuelled by SME and its blends, NOx emissions increased.