Abstract An experimental study on four electric gear urea pumps was carried out, and the variation rules of supply flow rate, speed, and volumetric efficiency of the urea pumps were obtained. Test ...results show that the volumetric efficiency will be affected by the coupling of multiple factors simultaneously, showing complex nonlinearity. A simulation model whose accuracy was verified by test data was established for analyzing the influencing factors of supply performance. With the increase in speed, the variation of volumetric efficiency has a linear relationship with the change of radial clearance and a quadratic parabola relationship with the change of axial clearance. In the range of working speed, the influence of radial clearance on volumetric efficiency is more significant, while the influence of axial clearance on volumetric efficiency will be gradually enhanced with increasing speed. The radial tolerance range should be as small as possible to ensure the consistency of the urea pump’s volumetric efficiency.
•Backfire origins of hydrogen fuelled engines are comprehensively reviewed.•Backfire control technologies of hydrogen engines are detailed discussed.•Correlations between various backfire origins are ...analyzed.•Different backfire control technologies are recommended adopting jointly.
Hydrogen fuel applications in internal combustion engines have attracted increasing attention due to zero carbon emission and excellent combustion characteristics in terms of thermal efficiency. Internal combustion engines fuelled with hydrogen are demonstrated to have higher brake thermal efficiency than other fossil fuel cases. However, abnormal combustion such as backfire in port hydrogen injection engines limits the improvement of internal combustion engine performance resulting from low ignition energy and high flame propagation velocity of hydrogen fuel. Volumetric efficiency drops significantly if backfire occurs; moreover, it brings about damages to the intake systems and fuel injection systems. Backfire is induced by high temperature residual exhaust gas, hot spots, and abnormal discharge of spark plugs; all the factors causing pre-ignition of hydrogen-air mixture promote the backfire occurrences. This paper reviews the factors tending to induce backfire, such as improper intake valve timing and fuel injection timing, and high fuel-air equivalence ratios; additionally, the corresponding backfire control strategies are analyzed with advantages and disadvantages being discussed. The factors leading to backfire are mainly caused by large amounts of residual exhaust gas, extremely slow combustion, and improper hydrogen distributions around intake valve seats. Backfire control strategies have specific application conditions to ensure their effectiveness, beyond which they will generate negative impacts on backfire control effectiveness. Power loss is nearly inevitable for naturally aspirated engines when backfire control strategies are adopted. Multiple control strategies are recommended to ease the engine performance drop caused by backfire control; meantime, multi-objective optimizations are suggested to achieve the optimal global performance.
•Novel variable-length manifolds are proposed for a 4-cylinder spark ignition engine.•A new 1D-3D coupled method is utilized for problem simulation.•Thermal, fluid-flow, heat, and mass transfer ...criteria are defined to evaluate the proposal.•Results improved the thermal efficiency, fuel consumption and heat release rate of the engine.
In current investigation, an innovative variable-length intake manifold is proposed for a 4-cylinder spark ignition engine to raise volumetric efficiency. Unlike common variable-length manifolds that operate solely on the basis of adjusting the optimal length of the inlet duct, in this proposed design, in addition to changing the optimal length by using different throttles, a non-linear combination of different throttles at different engine speeds is used. In addition, the effect of connecting the runners of cylinders no.1 and no.2, and cylinders no.3 and no.4 to each other with three different diameters is also investigated, and the innovation of this study is considered. To prove the efficiency of the new design, firstly, a stock engine is modeled utilizing the GT-Power software in wide-open throttle mode and then validated with the experimental results and previous studies then with the direct coupling of the model to the 3D Converge Lite solver. The proposed variable-length intake manifold with different throttle bodies is analyzed and reviewed in a one-dimensional-three-dimensional way. The results of using the proposed manifolds illustrated that by using a non-linear combination of throttle bodies and variable connection of runners in the entire speed range of the engine, the volume efficiency, thermal efficiency, torque, and effective specific fuel consumption of the engine are improved compared to the stock model by 5.17%, 0.67%, 5.90%, and 0.66%, respectively.
•The performance of transcritical CO2 heat pump system is experimentally studied.•The COP of vapor-injected cycle outperforms single-stage cycle by 6.21%.•Factors affecting the volumetric efficiency ...of the compressor are analyzed.
The accelerated advancement of the economy has led to a heightened focus on the issue of energy conservation and reduced consumption within heat pump systems. An experimental investigation was conducted to analyze the impact of discharge pressure and outlet water temperature on the performance of the transcritical CO2 single-stage heat pump system and vapor injection heat pump system. The experimental results show that the heating capacity first increases and then tends to be constant or even slightly decreases with the increase of discharge pressure in single-stage heat pump system. When subjected to the same operating conditions, the coefficient of performance of vapor injection heat pump system exceeds that of single-stage heat pump system. Compared with single-stage heat pump system, the performance coefficient of vapor injection heat pump system has increased by an average of 6.21% and the heating capacity has increased by an average of 9.54%. Additionally, the volumetric efficiency of the compressor substantially decreases when producing high-temperature hot water. Semi-empirical models for evaluating the compressor performance in both single-stage heat pump system and vapor injection pump system are established through the parameterization of the volumetric efficiency with respect to the pressure ratio and compressor speed. These models effectively forecast compressor performance.
Accurate in-cylinder air mass flow estimation is important for reducing emissions and improving the fuel efficiency of gasoline engines. Especially, the air-fuel ratio (AFR) control for gasoline ...engines is directly affected by the air mass flow estimation, which is used in feedforward control. At present, the transient air intake estimation for an engine is much more complex than the steady-state case. In practice, the working conditions of gasoline engines are always changeable to adapt to different traffic conditions, so it is important to improve the air intake estimation under the transient conditions. In order to improve the accuracy of intake air estimation, an appropriate filtering method is designed to eliminate the periodic fluctuations of the signals. And an estimation method based on the map self-learning algorithm is proposed, which considers the full working state of the engine, especially the transient conditions. The convergence of the proposed algorithm is guaranteed theoretically, and the method is designed to realize real-time identification and recursively correct of the volumetric efficiency value. The parameters of the observer are designed and adjusted through experiments to verify the effectiveness of the algorithm. With the continuous recursion of the algorithm, the accuracy of the air intake estimation will be improved and the error will be reduced. At last, the proposed strategy is analyzed and verified by a large number of experiments on the engine test bench to show its promising potentials.
The low volumetric efficiency of the diaphragm compressor under hydrogen refueling process, which hereby results in poor energy efficiency and high cost of hydrogen applications, should be paid ...attention to. This paper presents theoretical analysis and experimental investigation of the factors affecting the volumetric efficiency of the diaphragm compressor for hydrogen refueling process, focusing on the influence of hydraulic oil compressibility. A mathematical model was established to estimate the volumetric efficiency of diaphragm compressors, in which the effects of clearance volume, superheating of suction gas and pressure loss were taken into account and the emphasis was focused on the compressibility of hydraulic oil. A test rig was built to validate the theoretical model and further experimental investigations were carried out to identify the factors influencing the oil compressibility and hereby the volumetric efficiency. The volumetric efficiency was measured and compared under varied oil compressibility conditions by varying elastic modulus, oil overflow pressure and oil volume. The results indicated that the measured volumetric efficiency agrees well with the calculated value. The compression and expansion of hydraulic oil have a dominant influence on the volumetric efficiency, resulting in a loss of 37% of volumetric efficiency as compared to 2.4%, 18% and 1%, respectively for losses associated with clearance volume, superheating of suction gas and pressure loss, for a diagram compressor under refueling conditions with suction pressure of 30 MPa and discharge pressure of 90 MPa. The volumetric efficiency reduced rapidly with the increased oil overflow pressure, at a rate of 5% decrease with every 10 MPa rise in oil overflow pressure. As the oil volume increased by 100% of the stroke volume, the volumetric efficiency droped by 5.5%.
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•A volumetric efficiency model with oil compressibility effects was established.•Oil compressibility had a major effect on the volumetric efficiency.•Major factors on oil influencing volumetric efficiency were quantitatively estimated.•Oil volume should be designed less than 3 times stroke volume.
In terms of waverider’s aerodynamic performance degradation due to the design of increasing volume in engineering, it’s a solution to improve the design operations referring to area rule. With theory ...analysis and numerical simulation, the application of supersonic area rule at hypersonic speed was studied; an improved shape modification method based on area rule was developed and validated. The research results could support the design of improving volumetric efficiency of waverider and showed as follows: Object is supposed to be slender enough to ensure supersonic area rule’s application accuracy at hypersonic speed, which indicates the challenge to apply supersonic area rule to practical hypersonic vehicle due to unsatisfactory geometrical character; referring to some scholars’ development of area rule at hypersonic speed, improved shape modification method based on transonic area rule was developed and the influence of object’s geometrical character on drag reduction at hypersonic speed was studied; Applying the improved shape modification method, the modified combination of volume body and waverider had the drag reduced by 4% and volume increased by 31%, volumetric efficiency increased by 5%.
Hypersonic waveriders are special shapes with leading edges coincident with the body's shock wave, yielding high lift-to-drag ratios. The waverider geometry results from streamline tracing using the ...solutions of a basic flow field such as the wedge or the cone for specified shock and base curves. The base and shock curves can be independently prescribed in the osculating cone method enabling a larger design space. Generally, low values of the conical shock angle (9∘−15∘) are used. The lack of any method to limit the maximum cone angle for osculating cone waverider motivates this study. Mathematical expressions are derived for geometrical conditions that result in successful osculating cone waverider generation. A power law curve and a Bézier curve are analyzed. Closed-form expressions for the maximum cone shock angle are obtained for the power law curve. A numerical procedure to solve the same for the Bézier curve is developed. The results, for a typical Mach number of 6.0, evidently show that the maximum cone shock angle for successful waverider generation is significantly lower than the maximum angle for attached shock solutions. The limiting conditions developed will be essential in constraining the waverider sample space for automated multi-objective optimization routines. CFD simulations were conducted on waveriders designed with traditional shock angle of 12∘ and near limiting shock angle of 18∘. The analysis revealed a substantial 50% increase in volumetric efficiency, albeit with a minor decrease in aerodynamic performance. This highlights the critical need for determining the maximum conical shock angle when aiming for specific high volumetric efficiency.
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