Numerical Investigation of the Combined Influence of Three-Plug Arrangement and Slot Positioning on Wankel Engine Performance

A numerical methodology for three-dimensional fluid dynamics and chemical kinetics simulation of the combustion and gas-exchange processes in the Wankel engine was developed and validated. Two approaches of performance enhancement were studied—the addition of a slot in the rear side of the rotor recess, and installation of a third plug in the trailing side of the working chamber, in addition to the two available plugs mounted in the leading side of the baseline engine. The obtained results showed that the suggested three-plug arrangement significantly improves the engine performance. Furthermore, positioning the trailing plug further from the passage between the trailing and leading sides is of preference for higher mean in-chamber pressures. Nevertheless, for maximum performance, the distance should be brought to an optimum as during the intake stroke there is a loss of inducted charge due to backflow from the trailing plug hole. For the three-plug arrangement the presence of a slot is necessary for the prevention of early flame quenching in the trailing side, while keeping the added volume to a minimum. Moreover, positioning the slot and the trailing plug off-center, results in higher flow intensity towards the leading plugs, and accordingly, to a higher combustion efficiency. For dual-plug ignition system (two plugs in the leading side) it is preferable to maintain minimum clearance in the trailing side.

Total Plasma Homocysteine and Depressive Symptoms in Older Hispanics

Background: Very few studies have investigated the association between total plasma homocysteine (tHcy) and depressive symptoms in older Hispanics. Objective: To test the hypothesis that high tHcy associate with depressive symptoms in older Hispanics. Methods: A total of 1,418 participants .55 years old from the Maracaibo Aging Study (MAS) underwent standardized neurological, neuropsychiatric, and cardiovascular assessments. The Neuropsychiatric Inventory Depression Subscale (NPId) was used to assess the burden of depressive symptoms. The tHcy levels and other biochemical parameters in blood samples were measured. Multivariable logistic regression models were applied. Results: Participants with depressive symptoms had higher levels of tHcy than those without (15.1 versus 13.9 µmol/L; p = 0.009). Elevated tHcy levels were associated with depressive symptoms after adjusting for age, sex, education, smoking, diabetes, hypertension, alcohol intake, stroke, and dementia (OR = 1.62; 95% CI, 1.10–2.21). Conclusion: Elevated levels of tHcy level were associated with depressive symptoms in older Hispanics living under the nutritional and environmental conditions of a developing country.

Experimental and Numerical Analysis on the Influences of Direct Fuel Injection into Oxygen-Depleted Environment of a Homogeneous Charge Compression Ignition Engine

The oxygen-depleted environment in the recompression stroke can convert gasoline fuel into light hydrocarbons due to thermal cracking, partial oxidation, and water-gas shift reactions. These reformate species can influence the combustion characteristics of gasoline direct injection homogeneous charge compression ignition (GDI-HCCI) engines. In this work, the combustion phenomena are investigated using a single-cylinder research engine under a medium load. The main combustion phases are experimentally advanced by direct fuel injection into the negative valve overlap (NVO) compared with that of intake stroke under single/double pulse injections. NVO peak in-cylinder pressures are lower than that of motoring due to the limited O2 concentration, emphasizing that endothermic reactions occur during the overlap. This phenomenon limits the oxidation reactions, and the thermal effect is not pronounced. The 0-D chemical kinetics results present the same increasing tendencies of classical reformed species of rich-mixture such as C3H6, C2H4, CH4, CO, and H2 as functions of injection timings. Predicted ignition delays are shortened due to the additions of these reformed species. The influences of the reformates on the main combustion are confirmed by 3-D CFD calculations, and the results show that OH radicals are advanced under NVO injections relative to intake stroke injections. Consequently, earlier heat release and cylinder pressure are noticeable. Parametric studies on the effects of injection pressure, double-pulse injection, and equivalence ratio on the combustion and emissions are also discussed experimentally.

THE DEVELOPMENT OF ELECTRONIC CONTROL ALGORITHM OF FUEL ACTIVATOR INJECTION AT TWO-PHASE MIXTURE FOR-MATION IN AUTOMOTIVE DIESEL ENGINE

The article presents an algorithm of automatic control of injection of fuel activator supplied at the intake stroke into the intake manifold at two-phase mixture formation in the diesel engine. The algorithm represents a command set written in the microcontroller program of electronic control unit of the system performing the injection of fuel activator at the first phase of two-phase mixture formation.

Experimental and Numerical Analysis on the Influence of Direct Fuel Injection Into O2-Depleted Environment of a GDI-HCCI Engine

Injected gasoline into the O2-depleted environment in the recompression stroke can be converted into light hydrocarbons due to thermal cracking, partial oxidation, and water-gas shift reaction. These reformate species influence the combustion phenomena of gasoline direct injection homogeneous charge compression ignition (GDI-HCCI) engines. In this work, a production-based single-cylinder research engine was boosted to reach IMEPn = 0.55 MPa in which its indicated efficiency peaks at 40–41%. Experimentally, the main combustion phases are advanced under single-pulse direct fuel injection into the negative valve overlap (NVO) compared with that of the intake stroke. NVO peak in-cylinder pressures are lower than that of motoring, which emphasizes that endothermic reaction occurs during the interval. Low O2 concentration could play a role in this evaporative charge cooling effect. This phenomenon limits the oxidation reaction, and the thermal effect is not pronounced. For understanding the recompression reaction phenomena, 0D simulation with three different chemical reaction mechanisms is studied to clarify that influences of direct injection timing in NVO on combustion advancements are kinetically limited by reforming. The 0D results show the same increasing tendencies of classical reformed species of rich-mixture such as C3H6, C2H4, CH4, CO, and H2 as functions of injection timings. By combining these reformed species into the main fuel-air mixture, predicted ignition delays are shortened. The effects of the reformed species on the main combustion are confirmed by 3D-CFD calculation, and the results show that OH radical generation is advanced under NVO fuel injection compared with that of intake stroke conditions thus earlier heat release and cylinder pressure are noticeable. Also, parametric studies on injection pressure and double-pulse injections on engine combustion are performed experimentally.

Optimization of Direct Water Injection Parameters to Improve the Trade-off Between Efficiency and NOx Emissions for a Lean-Burn CHP NG Engine

In the medium and long term, cogeneration plants in Germany will play an important role in the transition towards a cleaner and more efficient electricity and heat generation, compared to the conventional uncoupled power plants. For most of the currently used CHP (Combined Heat and Power) units, which operate with a lean-burn process, the NOx emissions limit represents an obstacle to increasing the electrical efficiency. Therefore, the lean burn process has become less attractive because of stricter future NOx emissions limit. In this context, the stoichiometric combustion process with a three-way catalytic converter provides a solution. However, the present study shows that lean burn operation still has potential due to direct water injection into the combustion chamber. This work includes an experimental investigation of the impact of different injection parameters (beginning of injection timing, injection pressure difference and water-to-fuel ratio) on the effectiveness of direct water injection regarding the improvement of the trade-off between engine efficiency and NOx emissions. For the execution of the experimental investigations, a series-production CHP-engine was equipped with a direct injection system consisting of a high-pressure unit, a high-pressure pipe and a GDI-injector. For the injector integration, the cylinder head was machined sidewise (close to the exhaust gas valve). Furthermore, 3D CFD simulations of the injection process allowed gaining a deeper insight into the complex spray-flow interaction, wall film formation and evaporation at different injection timings. For the 3D CFD simulations, the spray model used was tuned with help of spray pictures, taken on the spray test bed. Water injection at the beginning of the intake stroke (330 °CA BFTDC) reduces NOx emissions most effectively. Moreover, it causes the least engine efficiency loss. The increase of the injection pressure difference (between 20 and 80 bar) leads to a significant increase of the engine efficiency. However, it has a secondary effect on the NOx emissions reduction. The lowest NOx emissions are reached with an injection pressure difference of 60 bar. The combination of direct water injection (at the beginning of the intake stroke, injection pressure difference of 60 bar) with earlier combustion phasings enables an increase in the engine efficiency and a simultaneous decrease in NOx emissions without loss in engine performance. Main drawbacks of water injection are longer combustion duration and higher CO and HC emissions. In addition, the lower exhaust gas temperature causes a deterioration of the conversion of the HC molecules in the oxidation catalyst and reduces the heat recovery efficiency of the CHP-system.

Controlling parameters of intake stroke of gas piston engines using the method of small deviations

A mathematical model of estimation of thermal and effective parameters of the most important part of cogeneration system of gas piston engine working in cogeneration mode was developed. Parameters of fresh air intake stroke with variable conditions of the environment using the method of small deviations were studied. The advantages of using the method of small deviations are the possibility of linearization of calculation equations as well as making calculations of not absolute but relative parameter change. The main parameters of fresh air intake by a cylinder are parameters of combustible mixture at the end of the intake stroke: combustible mixture pressure pa, the level of compression ε, the level of heating of fresh charge during the intake ΔT, parameters of residue gases (quantity Mr, pressure pr and temperature Tr), temperature of combustible mixture Tк. Using the method of small deviations for estimation of influence of the temperature of combustible mixture on effective values of gas piston engine led to an important finding: relative change of specific effective fuel consumption (economical part of gas piston engine exploitation) is in reverse relation to squared relative difference of temperature of supercharging air. In addition, cooling of supercharging air will positively influence temperatures inside engine cylinders and consequently fuel burning temperature. In turn, lowering the fuel burning temperature will improve ecological impact of the engine and reduce exhaust of harmful components into the atmosphere, in particular NOx.