Investigation of cylinder deactivation and variable valve actuation on gasoline engine performance

Increasingly stringent regulations on gasoline engine fuel consumption and exhaust emissions require additional technology integration such as Cylinder Deactivation (CDA) and Variable valve actuation (VVA) to improve part load engine efficiency. At part load, CDA is achieved by closing the inlet and exhaust valves and shutting off the fuel supply to a selected number of cylinders. Variable valve actuation (VVA) enables the cylinder gas exchange process to be optimised for different engine speeds by changing valve opening and closing times as well as maximum valve lift. The focus of this study was the investigation of effect of the integration of the above two technologies on the performance of a gasoline engine operating at part load conditions. In this study, a 1.6 Litre in-line 4-cylinder gasoline engine is modelled on engine simulation software and simulated data is analysed to show improvements in fuel consumption, CO2 emissions, pumping losses and effects on CO and NOx emissions. A CDA and VVA operating window is identified which yields brake specific fuel consumption improvements of 10-20% against the base engine at engine speeds between 1000rpm to 3500rpm at approximately 12.5% load. Highest concentration of CO emissions was observed at between 4 to 5 bar BMEP at 4000rpm and highest concentration of NOx at the same load range but at 1000rpm.Findings based on simulation results point towards significant part load performance improvements which can be achieved by integrating cylinder deactivation and variable valve actuation on gasoline engines. Copyright © 2014 SAE International

COMPARISON OF FLOW FIELD BETWEEN STEADY AND UNSTEADY FLOW OF AN AUTOMOTIVE MIXED FLOW TURBOCHARGER TURBINE

Global decarbonizing efforts in transportation industry have forced the automotive manufacturers to opt for highly downsized high power-to-weight ratio engines. Since its invention, turbocharger remains as integral element in order to achieve this target. However, although it has been proven that a turbocharger turbine works in highly pulsatile environment, it is still designed under steady state assumption. This is due to the lack of understanding on the nature of pulsating flow field within the turbocharger turbine stage. This paper presents an effort to visualize the pulsating flow feature using experimentally validated Computational Fluid Dynamics (CFD) simulations. For this purpose, a lean-vaned mixed-flow turbine with rotational speed of 30000 rpm at 20 Hz flow frequency, which represent turbine operation for 3-cylinder 4-stroke engine operating at 800 rpm has been used. Results indicated that the introduction of pulsating flow has resulted in more irregular pattern of flow field as compared to steady flow operation. It has also been indicated that the flow behaves very differently between pressure increment and decrement instances. During the pressure decrement instance, flow blockage in terms of low pressure region occupies most of the turbine passage as the flow exit the turbine

Drawbacks on the application of nozzle vanes in turbocharger turbine under pulsating flow conditions

It is commonly agreed that a turbocharger turbine behaves differently between steady and pulsating flow operations. This is due in no small part to the flow field distribution within the turbine stage. The use of nozzle vanes has significantly increased the three-dimensional complexity of the flow field, although some argue that the use of such stator could lead to improved overall turbine performance. This research investigates the drawbacks on the circumferential flow angle distributions due to existence of nozzle vanes particularly during pulsating flow conditions. In achieving this objective, a validated full stage unsteady CFD model was built to gain insight of the flow field behaviour. The results indicate that application of nozzle vanes has favourable effect on flow angle distribution at the rotor inlet during steady state operations for both design and off-design conditions. This is achieved in such a way that the existence of nozzle vanes has reduced the fluctuation of flow angle as compared to the flow upstream the vanes. On the other hand, during pulsating flow turbine operation, the fluctuation amplitude has spiked almost 400% the level of its counterpart under steady state operation at the rotor inlet. This behaviour could potentially have adverse effect on flow field distribution within the turbine passage and as such, reducing unsteady turbine efficiency

Non-adiabatic pressure loss boundary condition for modelling turbocharger turbine pulsating flow

This paper presents a simplified methodology of pulse flow turbine modelling, as an alternative over the meanline integrated methodology outlined in previous work, in order to make its application to engine cycle simulation codes much more straight forward. This is enabled through the development of a bespoke non-adiabatic pressure loss boundary to represent the turbine rotor. In this paper, turbocharger turbine pulse flow performance predictions are presented along with a comparison of computation duration against the previously established integrated meanline method. Plots of prediction deviation indicate that the mass flow rate and actual power predictions from both methods are highly comparable and are reasonably close to experimental data. However, the new boundary condition required significantly lower computational time and rotor geometrical inputs. In addition, the pressure wave propagation in this simplified unsteady turbine model at different pulse frequencies has also been found to be in agreement with data from the literature, thereby supporting the confidence in its ability to simulate the wave action encountered in turbine pulse flow operation

Developing an effective forest therapy program to manage academic stress in conservative societies: a multi-disciplinary approach

We conducted a multi-disciplinary research to develop a forest therapy program that could manage academic stress in students. The first part of the study comprised of a survey to develop a forest therapy program based on the expectations of students, and involved 412 students aged 19–24 years (21.73 ± 2.33 years). The second part was a field study to determine the sustained effects the forest therapy program had on the blood pressure of students, involving twenty-nine students aged 21–23 years (21.83 ± 0.711). The survey determined that students were suffering from academic stress but their fear of societal stigma prevented them from seeking assistance. The majority (57.26%) expressed interest in forest therapy, and wanted a half-day forest therapy program during the weekend. Systolic (SBP) and diastolic (DBP) blood pressure were used as measurement indices for the field study, and was conducted before breakfast, lunch and dinner. Readings were taken 3 days before (baseline values), during, 3, 5 and 7 days after the forest therapy program. The blood pressure reading 3 days prior to the program served as a representation of the participants’ every blood pressure levels. When compared to the everyday blood pressure levels (124/81 mmHg), both the SBP and DBP significantly decreased during the forest therapy (117/77 mmHg), and the decrement maintained 3 days (114/77 mmHg) and 5 days after (118/79 mmHg). There was no significant decrease in blood pressure between the everyday levels and 7 days after. In conclusion, a half-day forest therapy program is able to decrease students’ SBP and DBP, and the decrements were maintained for 5 days. The exit survey reaffirmed the blood pressure results, whereby the participants believed that forest therapy had reduced their stress

Discharge and flow coefficient analysis in internal combustion engine using computational fluid dynamics simulation

Intake system is one of the crucial sub-systems in engine which can inflict significant effect on the air-fuel mixing, combustion, fuel consumption, as well as exhaust gases formation. There are many parameters that will influence engine performances. Good engine breathing is required to get better air flow rate to the engine. One of the methods includes the improvement of intake system by modifying the intake port design. This paper presents the application of Computational Fluid Dynamics analysis on two engines with different intake port shapes. Dimensionless parameters like discharge coefficient and flow coefficient are used to quantify the changes in intake flow at different valve lifts variation. Results show that when valve lift increases, this inflicted the increase in discharge coefficient because of greater mass flow rate of induction air. Both flow and discharge coefficient is dependent on valve lift. Flow analysis proved the relationship by computing the increase of flow coefficient as valve opening increase. The computed analysis shows that different intake port shapes does bring significant effect on discharge coefficient and flow coefficient

Suppression of tonal noise in a centrifugal fan using guide vanes

This paper presents the work aiming for tonal noise reduction in a centrifugal fan. In previous studies, it is well documented that tonal noise is the dominant noise source generated in centrifugal fans. Tonal noise is generated due to the aerodynamic interaction between the rotating impeller and stationary diffuser vanes. The generation of tonal noise is related to the pressure fluctuation at the leading edge of the stationary vane. The tonal noise is periodic in time which occurs at the blade passing frequency (BPF) and its harmonics. Much of previous studies, have shown that the stationary vane causes the tonal noise and generation of non-rotational turbulent noise. However, omitting stationary vanes will lead to the increase of non-rotational turbulent noise resulted from the high velocity of the flow leaving the impeller. Hence in order to reduce the tonal noise and the non-rotational noise, guide vanes were designed as part of this study to replace the diffuser vanes, which were originally used in the chosen centrifugal fan. The leading edge of the guide vane is tapered. This modification reduces the strength of pressure fluctuation resulting from the interaction between the impeller outflow and stationary vane. The sound pressure level at blade passing frequency (BPF) is reduced by 6.8 dB, the 2nd BPF is reduced by 4.1 dB and the 3rd BPF reduced by about 17.5 dB. The overall reduction was 0.9 dB. The centrifugal fan with tapered guide vanes radiates lower tonal noise compared to the existing diffuser vanes. These reductions are achieved without compromising the performance of the centrifugal fan. The behavior of the fluid flow was studied using computational fluid dynamics (CFD) tools and the acoustics characteristics were determined through experiments in an anechoic chamber

Effects of mechanical turbo compounding on a turbocharged diesel engine

This paper presents the simulation study on the effects of mechanical turbo-compounding on a turbocharged diesel engine. A downstream power-turbine has been coupled to the exhaust manifold after the main turbocharger, in the aim to recover waste heat energy. The engine in the current study is Scania DC13-06, which 6 cylinders and 13 litre in capacity. The possibilities, effectiveness and working range of the turbo compounded system were analyzed in this study. The system was modeled in AVL BOOST, which is a one dimensional (1D) engine code. The current study found that turbo compounding could possibly recover on average 11.4% more exhaust energy or extra 3.7kW of power. If the system is mechanically coupled to the engine, it could increase the average engine power by up to 1.2% and improve average BSFC by 1.9%

Downsizing Capability Evaluation of Active Control Turbocharger (ACT)

This study aims to evaluate the downsizing capability of active control turbocharger (ACT) by means of computer simulation approach. One dimensional simulation package was used to model a commercial 13L diesel engine equipped with variable geometry turbocharger (VGT) and a 10L diesel engine equipped ACT. The 10L ACT engine delivered up to 34.42% of higher brake power than 13L VGT engine at 1000RPM and below, but for the higher engine speed, 13L VGT engine delivered higher brake power (up to 14.5%) than 10L ACT engine

Pressure distribution on the blade surface of an automotive mixed flow turbocharger turbine under pulsating flow conditions

The increment of the contribution to CO2 release by transportation industry as other sectors are decarbonizing is evident. As number of world population continue to increase, the task of developing highly downsized high power-to-weight ratio engines are critical. Over more than a hundred years of invention, turbocharger remains a key technology that enable highly boosted efficient engine. Despite its actual operating environment which is pulsating flow, the turbocharger turbine that is available to date is still designed and assessed under the assumption of steady flow conditions. This is attributable to the lack of understanding on the insight of the flow field effect towards the torque generation of the turbine blade under pulsating flow conditions. This paper presents an effort towards investigating the influence of pulsating flow on the blade loading and its differences from steady state conditions through the use of Computational Fluid Dynamics (CFD). For this purpose, a lean-vaned mixed-flow turbine with rotational speed of 30000 rpm at 20 Hz flow frequency, which represent turbine operation for 3-cylinder 4-stroke engine operating at 800 rpm has been used. Results presented in terms of spanwise location of the blade indicated different behavior at each location. Close to the hub, there are strong flow separation that hinders torque generation is seen while at mid-span more torque is generated under unsteady flow as compared to its steady counterpart. Moreover, close to the shroud, the pressure difference between steady and pulsating flow is almost identical