Abstract

About nine million barrels of gasoline are consumed daily by automobile engines. Out of this, roughly 2.25 million barrels are effectively used by the engine to generate power, whereas the rest is wasted due to engine inefficiencies. There is a dire need to bring up a more efficient engine, since even an effort for a 1% increase in efficiency would result in savings of almost $6 million daily worldwide. In this study, first, a conventional poppet valve engine configuration for a 70cc engine was analyzed. Then, based on the engine efficiency contributing parameters, a novel Independent Rotary Valve (IRV) engine configuration was proposed. The proposed engine configuration was analyzed for the same 70cc engine. The LOTUS Engine software was used for the thermodynamic investigation of intake valve closing angle for getting maximum values of volumetric efficiency, brake power, and brake torque at different speeds and intake valve closing angles. It has been found that the proposed engine configuration resulted in approximately 1.165% increase in thermal efficiency by a decrease in air-fuel mixture pumping work. In addition, a 13% increase in volumetric efficiency, a 13% increase in brake torque, and an 18% increase in brake power were found, through the use of independent valve actuation. Also, an increase in mechanical efficiency is expected, due to the added simplicity of the proposed IRV as compared to the conventional poppet valve system. This increase has been verified analytically and by numerical modeling performed in ANSYS FLUENT. The proposed IRV engine configuration is thus a more efficient, more powerful, less complicated, more stable, and an environmentally safer engine.

Introduction

Engines are designed to be efficient so that the maximum work could be extracted for the same amount of fuel supplied [1]. The statistics presented in the literature on gasoline consumption clarifies the worth of increasing the efficiency of the engine.2 It is illustrated in the literature that almost 20% of the mechanical efficiency (nm) is lost in the cam valve configuration, by dissipation in the spring and the torque to drive this complex mechanism. Additionally, 50% of nm is lost in piston-cylinder arrangement [2,3]. The value of volumetric efficiency (nv) is also important to the performance of an engine, in particular at higher speeds [4]. It is seen that the effect of the valve timing and flow restriction on pressure drop in the intake manifold is most critical to nv. Volumetric efficiency increases as the lift and timing are increased for the same engine speed [57]. Volumetric efficiency is critical to high-speed performance, where choking takes place as engine valves find little time to actuate, and thus, lesser air enters the cylinder. The concept of choking has been explained in detail in the literature [8]. Choking limits engine operation at high speed and thus limits the performance characteristics to be maximum at a speed range of 2500–3000 rpm. A valve actuation optimization system is the only practical way to increase engine efficiency at all speeds [9].

Kakaee et al. [10] performed an optimization study using variable valve timing (VVT). It was found that there is a 5% decrease in brake-specific fuel consumption (BSFC), an increase of 3.5% in brake torque, and 2.9% in brake power. Additionally, it was found that a decrease of 10% BSFC resulted in an even more increased torque and power. Intake valve closing (IVC) timing is a fundamental element of controlling the volumetric efficiency and thus performance [6,11,12]. Cinar and Akgun [13] performed a study on IVC and found that there is an almost 5% increase in brake torque and 2–5% decrease in BSFC. However, the benefits of VVT or IVC are limited because these are mainly programmed to operate in two speed regimes, low end and high end.

A typical representation of the engine energy flow diagram and data on throttling shows that pumping loss, when wide open throttle (WOT) doesn’t exist, accounts for 1–4% loss of the available fuel energy. WOT operation in carburetor with throttling at the port by poppet valve is a plausible solution to the loss by pumping work (Wp) and thus to increase the thermal efficiency [14,15]. A system invoking the benefits of VVT as well as throttling losses has been introduced by FIAT as a multi-air system. It is found that there is a considerable increase in engine performance parameters [16]. However, this system has a major disadvantage. It becomes too much expensive and complicated to operate on electrohydraulic system installed on the top of the poppet valves. Other systems with overhead cam motors have been proposed by Camcon. These systems use conventional poppet valves and work on independent valve actuation.3 However, like the previous system, they suffer significant drawback as it does not completely work on throttle-less operation; rather just control the timing of valve.

Rotary valves have been known long since the poppet valves were. In fact, rotary valves have been idealized as the ultimate engine solution, with extensive research work of 15 years done by Cross, extensively indicating the benefits [17]. These benefits include high volumetric efficiency, higher compression ratio capability, lesser mechanical losses, and lesser mass on top of the engine. Remy and Hoi [18] performed a comparative study on rotary and poppet valves. It was found that there is an almost 23% increase in volumetric flowrate, with a design that involves axial port feeding to rotary valves. However, rotary valves have faced a major disadvantage. The sealing of rotary valves has never been completely addressed for most of the research work done earlier. As high-temperature seal materials have not been available then. Only now, with the recent improvements in elastic technology, with materials like Poly Tetra Fluoro Ethylene (TPFE) capable of bearing temperatures up to 600 K, with spring energized seals (with significantly less friction) have improved the prospect of incorporating seals with rotary valves. Thus, it is made possible to use rotary valves [19]. Coates spherical rotary valve (CSRV) is an example of this possibility [20].

Li et al. [21] studied the pumping losses of the continuous variable valve lift and variable valve timing engine. The pumping loss factors and mechanism were analyzed in the two mentioned engine types. It was found that the continuous variable valve lift engine has lower intake loss than variable valve timing engine due to different intake modes.

Kutlar et al. [22] studied different methods to improve the efficiency of the four-stroke engine at part load. It was concluded that the flow restriction at the intake section by partially closing the throttle valve leads to increased pumping losses and is the main reason for the efficiency drop.

Ortlieb et al. [23] studied the effect of valve pumping power on the efficiency of the engine. The effect of the different variables, i–e load variation, engine speed, and valve timings on valve pumping work was evaluated. The 1D-CFD simulation was utilized in their study. It was concluded that the valve pumping work consideration can increase the engine efficiency accuracy prognosis based on engine process simulations.

Zibani et al. [24] proposed a solenoid-operated stepping valve to replace conventional poppet valves to resolve the issue of piston-valve collision. Software was used to precisely control the valve events, resulting in improved efficiency of the engine. ALTERA’s QUARTUS II Development System was used to carry out the simulation of the proposed system.

Allawi et al. [25] studied the variable valve timing (VVT) of multi-cylinder, four-stroke, and spark engines to improve engine efficiency-related performance parameters. The Lotus Engine Simulation software was used in their study. One conventional and three other timing cases were considered in their study. The results showed that the overlap case of 98 deg has improved engine efficiency performance parameters, i–e volume efficiency, brake thermal efficiency, etc.

Keeping in view the available literature on different engine configurations of intake valve lift and timing control methods, it can be seen that there is no such configuration, to address intake flow restriction, pumping power losses, throttling losses, and independent valve actuation collectively at all speeds. In addition, all of the discussed systems in the literature rely on poppet valves, which do not make much difference to the flow restriction on the face of the poppet valve, and hence, it does not simplify the system. Based on the literature, it is required to design an engine with no additional cost and the least complexity. Further, in the scope of simplicity and additional benefits over the poppet valve, a rotary valve with axial port feeding was concluded earlier to be the most convincing solution. Based on the prior criteria, an innovative novel rotary engine valve configuration was proposed by addressing the aforementioned issues collectively. This novel engine configuration was named an Independent Rotary Valve (IRV) engine. The proposed rotary valve engine configuration was compared with the 70cc conventional poppet valve engine configuration using analytical and numerical techniques. The LOTUS Engine software was used for the thermodynamic investigation of the intake valve closing angle for getting maximum values of volumetric efficiency, brake power and brake torque at different speeds, and intake valve closing angles. It was found that the proposed IRV resulted in significant improvements in volumetric efficiency, brake torque, brake power, and thermal efficiency. The pressure loss and pumping work were calculated for 2000 and 5000 rpm (low speed and high-speed regimes) because, at these engine speeds, the engine performance parameters are more sensitive in terms of fuel consumption. The set of results that are calculated at these two engine speeds can be applied to various engine speeds in low- and high-speed regimes. The selection of the 2000 and 5000 engine speeds is also based on the outcomes of the thermodynamics engine simulations given in Figs. 24 and Table 4. It can be seen from Table 4 that the engine performance parameters are more sensitive at 2000 and 5000 engine speeds. This improvement was verified analytically and by numerical modeling performed in ANSYS FLUENT.

Materials and Methods

Governing Equations

Engine Efficiency.

The first step to model the parameters and measure correctly the benefits of any designed system was to clearly define the parameters of engine efficiency, termed as the overall efficiency (noverall) of the engine. For an engine to be efficient, it must have high values of the constituent efficiencies, i.e., mechanical efficiency (nm), volumetric efficiency (nv), and fuel-conversion efficiency (nf).

Equation (1) can be used to calculate the overall efficiency
noverall=nm×nf×nv
(1)

In order to model the overall efficiency, it is needed to characterize each of the aforementioned efficiencies.

Mechanical Efficiency.

Mechanical Efficiency attributes mainly to the frictional losses and other accessories upon which the additional work is done by the engine. It is given as [26]
nm=brakepowerindicatedpower
(2)
The relation for brake power (bP) is given as
bP=2πNT
(3)
where N is the engine number of revolutions and T is the torque.

This means that at higher speeds and torque, the value of brake power increases. There are several losses, which reduce the brake power and hence, the mechanical efficiency. These losses in mechanical efficiency can be attributed to a number of factors, friction being the major one of them.

A comparison of mechanical efficiency values provided in Ref. [26] is shown in Table 1.

Fuel-Conversion Efficiency.

Fuel-conversion efficiency is the collective efficiency of the combustion process (combustion efficiency (nc)) and the actual work done on the piston by the fuel during thermodynamic cycle (thermal efficiency (nt)). It is given as [26]
nf=nc×nt
(4)
Both the combustion and the thermal efficiencies can be easily determined. Combustion efficiency usually has a very high value, up to even 98%, meaning that combustion is normally completed and a small amount of unburnt mixture remains after the combustion. Therefore, thermal efficiency becomes the major factor of control in the design problems. In fact, it is only this thermal efficiency that has motivated designers since centuries, to develop new concepts from Otto to Miller cycles, and various other designs. The relation for fuel-conversion efficiency from the air standard cycle analysis is given as
nt=Wtnc×mf×QLHV
(5)
where Wt is the same as the net area under the cycle of the thermodynamic process, also called the thermal work, QLHV is the lower heating value of the fuel, and mf is the mass of fuel. This means that a higher thermal work obtained from the same amount of fuel energy corresponds to an increase in thermal efficiency. In reality, the thermal efficiency values are much lower. It is seen that the brake values of nt are 15% lower than the indicated values nt,i. Some typical numbers are given in Table 2.

Lower values of brake thermal efficiency are due to exhaust enthalpy losses, heat transfer losses, pumping losses, etc. Out of all these, pumping loss is the only parameter, which can be practically controlled in a dynamic automobile environment.

Volumetric Efficiency.

Volumetric efficiency is often expressed in terms of the mass flowrate of air entering the cylinder (m˙a) and is mathematically given as [26]
nv=2m˙aρa,o×Vd×N
(6)
where ρa,o is the density of air, Vd is the displaced volume, and N is the number of revolutions. Based on Eq. (6), the volumetric efficiency increases as the mass flow of air increases and decreases as the number of revolutions is increased. Table 3 shows a range of values for this efficiency.

Thermodynamic Simulations for the Effect of Variable Intake Valve Closing Angle

The LOTUS engine software was used for the thermodynamic investigation of the intake valve closing angle for getting maximum values of volumetric efficiency, brake power, BSFC, and brake torque at different speeds and intake valve closing angles. LOTUS engine software is capable of predicting the overall performance of an engine [27]. The main steps that were followed for the engine simulation in the LOTUS software are given below:

  • The engine and manifold specifications were provided as inputs to the software.

  • Once the engine specifications data and test condition data were entered, the cycle simulation was performed. The progress of the simulation results was monitored continuously using the Job Status screen.

  • The calculation results for cycle-averaged data, such as volumetric efficiency, BSFC, torque, and power, were plotted using quick-to-use graph plotting systems.

The Intake Valve Closing Angle has a great effect on the performance and volumetric efficiency. Usually, the value of IVC is fixed in a conventional engine but the engine performance is not maximum at each engine speed. However, there is an optimum IVC value, for which the performance parameters are maximum at every engine speed. In order to check for the variation of volumetric efficiency and related parameters (torque, power, BSFC) by changing the valve timing, a parametric study was performed using LOTUS Engine software [28]. For an engine with a carburetor, the speed was varied from 1000 to 7000 rpm for the stoichiometric mixture. A demonstration of the circuit used in this simulation is provided in Fig. 1.

Using the simulation techniques, plots for parametric study of IVC, ranging from 15 deg before bottom dead center (BBDC) to 120 deg after bottom dead center (ABDC) was developed. Figure 2 shows the trend of volumetric efficiency over the above-mentioned range, obtained from simulation. Note that in Fig. 2, at the IVC value of 15 deg and 2000 rpm, the maximum volumetric efficiency of 89% is obtained. This value decreases sharply to 42% at 7000 rpm. This is consistent with the theory of VVT and Eq. (6), meaning that the valve close time should be altered to the optimum at every rpm or range of rpm. At 5000 rpm, the volumetric efficiency at 80 deg ABDC is 70%, whereas, at the previously maximum point of 15 deg after bottom dead center (ABDC), the value is only 57%. This corresponds to about a 13% improvement in volumetric efficiency with a mechanism employing variable IVC.

It can be seen in Fig. 3 that the brake power is highest at high rpm. However, choosing a maximum volumetric efficiency point of 15 deg ABDC would give the maximum power of 11 kw at 4000 rpm, whereas at 80 deg ABDC, the value of power increases to about 13 kw. This shows a 2 kw or about 18% increase in brake power with variable IVC.

In Fig. 4, it can be seen that the brake torque decreases at higher speeds. However, operating at about 65 deg ABDC can give a torque boost of about 4–5 Nm, equivalent to a 13% increase with variable IVC. In Fig. 5, it can be seen that at low and high speeds the magnitude of the break-specific fuel consumption (BSFC) is high.

In Table 4, all the obtained results have been tabulated on the basis of five ranges of rpm so that the IVC angle and their effect on efficiency can be depicted more clearly.

The engine size/geometry varies from one automobile to the other, which will affect the magnitudes of power and torque values. However, the percentage increase in the values of parameters remains almost the same. This is verified by the consistency of this work with related research works by Refs. [10,13,18] on VVT for intake valve.

Calculations for Pressure Drop and Pumping Work on Conventional Poppet Valve Configuration

Another problem that can affect the thermal efficiency nt,b is the pumping work [15]. In the current study, the actual value of pumping work (in a real engine) was evaluated by choosing a particular geometry. The choice of geometry of the engine was critical because the fluid dynamics calculations greatly depend on geometry. In this study, a single-cylinder 70cc carbureted (round slide carburetor) gasoline engine was used. The geometries used for the intake and carburetor, in the case of the poppet valve, are given in Figs. 6 and 7.

The knowledge of conservation of mass, momentum, and energy was applied to calculate the losses in each case. Since the piston intake stroke pull air into the cylinder, it was plausible to assume engine as a constant volume flowrate device, like a pump. Thus, at any section in the intake, either in the carburetor or at the throat of the valve, the volume flowrate Q˙ is given by
Q˙=A×v
(7)
Where, A is the cross-sectional area and v is the velocity. The steady flow energy Eq. (8) was used with head loss [29,30], assuming the flow was incompressible (no temperature or compression effects are dominant). Also, gravitational effects were neglected for this geometry.
P1ρg+v122g=P2ρg+v222g+hf+hm
(8)
where P1/ρg is the pressure head at Sec. 1, v12/2g is the velocity head at Sec. 1, P2/ρg is the pressure head at Sec. 2, v22/2g is the velocity head at Sec. 2, hf are the minor losses, and hm are the major losses. The value for v2 could be found using the value of Q at each rpm. Then, the pressure drop could be found using the major and minor losses calculated from geometry, with the added condition of zero bulk velocity and atmospheric pressure. The major loss in the carburetor was found by incorporating the mean diameters of the converging and diverging section of the carburetor. Further, the mean diameter and mean arc length of the bend, coupling the carburetor to the head, were used to find the major loss in that section. The poppet valve section was divided into two zones: one with simple cylindrical section, and the other as an annulus until point B, as shown in Fig. 6.
The minor losses for the carburetor were found by taking the contraction and expansion zone effects into consideration, along with the coupling bend of the carburetor. At the throat of the carburetor, a gate-type sliding throttle valve was incorporated in minor loss calculation, based on the real geometry. Since the suction was done using atmospheric air, the value of minor loss coefficient K discussed by White [30] could not be used. If that data were used, ΔP would be too large for atmospheric pressure, and it would have indicated negligible flow, which was not correct. Since insufficient literature was available in this regard, the computationally found values of K were used in this study. For the case of the poppet valve, the entrance effects, restriction at the poppet face, sudden expansion in the cylinder, and the bend in the manifold had been taken into consideration. In order to make quick design decisions, a program was formulated, which gave the pressure drop (PAPB) and also the pumping work (Wp) (for any geometry) from the following relation [23]:
Wp=(PAPB)Vd
(9)
where Vd is the displaced volume.

Summary of Results.

The obtained results from the calculations have been summarized in Table 5. The indicated work done found by air standard cycle calculations equals to be 133 J. Thus, these values correspond to a decrease of 1.218% (1.62133*100) of thermal efficiency at 2000 rpm and 0.632% (0.84133*100) of thermal efficiency at 5000 rpm. These calculations give approximate solutions based on the analysis performed at the instant when the flow is fully developed i.e., steady-state. In reality, the flow develops with time as suction takes place. Here, it is apparent that a significant loss occurs at the throttle valve and then at the poppet valve face. A system outweighs these losses with a throttle-less flow, and no flow restriction at the poppet valve face will certainly have high thermal efficiency values. The pressure drop values are much related to the values concluded by [31].

Proposed Concept for Increasing Internal Combustion Engine Efficiency

The usefulness of variable intake valve closing angle with engine speed was a much-needed solution to improve engine volumetric efficiency and performance characteristics. Also, a system with throttle-less flow with no restriction at the poppet valve was much needed to increase the thermal efficiency of the engine. The loopholes of systems [16]4 discussed earlier, require coming up with a system with no additional cost and the least complexity. In the scope of simplicity and additional benefits over poppet valves, rotary valves with axial port feeding were concluded earlier to be the most convincing solution. Based on the prior criteria, an innovative solution was developed by combining the advantages of all the aforementioned characteristics into a single system, which we called the IRV engine. The modeling was performed on the same basic geometry of the single-cylinder 70cc engine as was considered earlier in calculations. Figure 8 shows a photo-rendered model of this proposed engine.

Working of the Proposed Independent Rotary Valve Engine.

The independent rotary valve engine is operated by using two concentric rotary shafts with axial port feeding. One of the shafts is for throttling (as well as IVC angle control) and the other for port feeding. Instead of using a high-speed bidirectional motor, a normal-speed bidirectional motor is used. These shafts are held in place with tight tolerance using bearings. Seals on either side of the gaps ensure that no gas leakage occurs. Thus, a single valve controls the throttling and the IVC angle, simultaneously. This is thus a novel idea to implement VVA and WOT operation collectively, with throttling at the intake port of the cylinder as shown in Figs. 9 and 10.

Figures 811 show the different views of the proposed IRV engine. Figure 12 shows the cross-sectional view of the conventional original engine. The proposed IRV engine in comparison to the conventional engine has no poppet valve and cam for driving the poppet valves. In the proposed IRV engine, the poppet valves are replaced with rotary valves.

Calculations for Pumping Work for the Proposed Independent Rotary Valve Configuration

The next step was to check for the savings in pumping work and pressure drop obtained from the proposed engine configuration. This was done using the same theory, as discussed earlier. The geometries used for intake of the rotary valve and carburetor are given in Figs. 13 and 14.

The size of the rotary valve was taken as 20 mm, equivalent to the poppet valve port diameter, as the choice for comparison. Here, the carburetor section did not contain any throttle restriction, whereas there were only expansion effects in minor losses at the throat of the cylinder. Also, the restriction at the poppet face was not present. This reduced the high losses in the engine.

Findings From Analysis.

The results obtained from the calculation are given below in Table 6. It can be seen that at 2000 rpm, an increase of almost 1.165% (1.620.07133*100) thermal efficiency is possible, whereas, at 5000 rpm, an increase in thermal efficiency is of 0.42% (0.840.28133*100).

Based on the summary of the results in Tables 5 and 6, it can be clearly seen that pumping work has been excessively reduced for the IRV engine as compared to the conventional poppet valve system at both 2000 rpm and 5000 rpm. The difference in IRV and poppet valves is less at high rpm because the effect of restriction by throttle decreases, and thus, the pumping work also decreases and becomes comparable. Further, lower values of pumping work at 2000 rpm are due to the lower velocities at the intake than at 5000 rpm.

Computational Fluid Dynamics Analysis of the Two Configurations

ANSYS Fluent software was used for the numerical analysis of the conventional poppet valve and proposed IRV engine. ANSYS Fluent is an advanced CFD software that can be used to perform complex simulations easily. It can be used to simulate fluids’ flow, heat transfer, and fluid–structure interactions. The flow of gases, liquids, and multiphase fluids, as well as reacting systems and structural analysis, can be modeled in ANSYS Fluent. It can be used in a variety of applications, including aerospace, automotive, chemical, and many more. The finite volume method is used in ANSYS Fluent for solving the governing equations of fluid flow and heat transfer. The domain of the simulation is divided into a series of small, interconnected control volumes or cells during the modeling process. During the modeling, the values of the variables under study are calculated at the centroids of these cells. A converged solution is obtained in ANSYS Fluent using iterative algorithms [33].

The following steps were performed during the numerical study:

  • Developed the CAD model of the poppet valve and IRV geometry in CREO Parametric.

  • The developed geometries were imported into ANSYS Fluent module.

  • The CAD geometries meshed in ANSYS Fluent.

  • The boundary conditions along with the flow model were selected.

  • The flow solver controls were set.

  • The transient simulations were run till convergence.

  • The contours for static pressure were obtained from the post processing section.

Computational fluid dynamics is a vital tool to effectively predict and validate flow and associated flow phenomena. In the current study, it is used to verify the theoretical results of pressure drop for the rotary and poppet valve arrangements. In order to model the suction of the engine during intake, a transient analysis with dynamic mesh is performed on the piston surface. This surface was translated with reference to the rpm in a downward direction. This has made it possible to correctly model the intake process of an engine. The effects at the runner and carburetor section were also included.

Proposed Independent Rotary Valve System.

The mesh optimization study was performed for the IRV system, as shown in Fig. 15. The solution becomes almost constant as the number of total mesh elements increased beyond 32,127, so this number of mesh elements was used in the numerical modeling.

CFD modeling was performed on the proposed IRV configuration, which resulted in significantly low pumping loss in the case of rotary valves, as was expected from the theoretical calculations. The optimized meshed geometry of the proposed IRV configuration is shown in Fig. 16.

The boundary conditions for the IRV value model are shown in Fig. 17. Inlet pressure condition is applied at the inlet section of the IRV configuration. The value of the pressure is set to zero-gauge pressure. All the walls surrounding the fluid geometry of IRV are set to stationary walls with no-slip condition. The piston is set to a rigid body in IRV. The cylinder is set to a deformable body in the case of IRV. The analysis performed was pressure-based transient analysis. The k-epsilon, realizable model with scalable wall function was used for the analysis of IRV.

Findings.

Using the transient analysis, the pressure contours were developed for the proposed rotary valve as shown in Figs. 18 and 19. It can be seen clearly that the pressure contours have significantly less value. This confirms the effectiveness of throttle-less flow in the proposed rotary valve configuration.

The results obtained by the two analyses for the IRV valve at points A and B are compared in Table 7. Here, these two points are important for the analysis of port flow. One is right after the carburetor, and the other is right at the port. The values of pressure at these two points form the basis for calculating the pumping work.

The contours of pressure at the engine rpm in Figs. 18 and 19 are in good agreement with the theoretical predictions. The pressure images at different time-steps for the rotary valve at 5000 rpm are shown in Fig. 20.

Conventional Poppet Valve System.

For the case of the poppet valve, the throttle body in the carburetor section was included. The throttle plate was taken as the gate valve (as in calculations). From linear interpolation, the opening length of the valve was taken to be 4 mm (out of 14 mm) at 2000 rpm and 10 mm at 5000 rpm. For the purpose of simplifying the analysis, a lift of a constant mean value of 4 mm was considered, whereas the maximum lift was 6 mm, since it was an instantaneous value and was not effective. The boundary conditions for the poppet value model are shown in Fig. 21. Inlet pressure condition is applied at the inlet section of the poppet valve. The value of the pressure is set to zero-gauge pressure. All the walls surrounding the fluid geometry of the poppet valve are set to stationary walls with no-slip conditions. In the case of the poppet valve, its outer surfaces are set to stationary walls. In modeling the geometry, the poppet valve is excluded from overall fluid geometry. The piston is set to a rigid body in the case of the poppet valve. The cylinder is set to the deformable body in the case of the poppet valve. The analysis performed for the case of the poppet valve was pressure-based transient analysis. The k-epsilon, realizable model with scalable wall function was used for the analysis of the poppet valve.

Findings.

Using the transient analysis with a k-epsilon scalable wall function model, and fluid as air with constant density, the following results are obtained as shown in Figs. 22 and 23, respectively.

The results obtained by the two analyses for the poppet valve at points A and B are compared in Table 8. Here, these two points are important for the analysis of port flow. One is right after the carburetor, and the other is right at the port. This indicates the loss after the throttle and loss as it enters the port. This value forms the basis for calculating the pumping work.

It can be seen that the value of pumping work obtained by this calculation was small as compared to the theoretically calculated value. The reason was that in the theoretical calculation, a number of factors like gradual expansion, bend in manifold, etc., were accounted, which were not present in this simplified CFD model. Also, the transient analysis was not considered in the theoretical analysis, which accounted for a certain developing flow region as well. Lastly, an important deduction from this CFD analysis was that the pumping work in the case of throttle-less rotary valves was very less as compared to the poppet valve. This means that the gains predicted in the theoretical results are true and verified.

Conclusion

In the current study, a novel independent rotary valve engine system was proposed. The IRV system comprises rotary valves and bidirectional electronic motor that controls the throttling and the intake valve closing angle of the proposed system. The outer rotary valve is for synchronization and port feeding. A comparative analysis was performed between the conventional poppet valve system and the proposed IRV system. The current work results showed that the proposed IRV system resulted in a 13% increase in volumetric efficiency, a 13% increase in brake Torque, an 18% increase in brake power, a 1.165% increase in thermal efficiency at 2000 rpm, achievement of higher compression ratios, higher mechanical efficiency due to lesser moving parts, and lesser inertia on top of the engine and thus more stable engine.

In short, it was found that the IRV system is an effective, simple, and multiple benefit solution to increase internal combustion engine efficiency.

Footnotes

Acknowledgment

The authors appreciate and acknowledge the support provided by King Fahd University of Petroleum and Minerals (KFUPM) by providing all the essential resources to conduct this study.

Conflict of Interest

There are no conflicts of interest. This article does not include research in which human participants were involved. Informed consent is not applicable. This article does not include any research in which animal participants were involved.

Data Availability Statement

The data sets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request.

Nomenclature

N =

engine speed (rpm)

T =

torque

Q˙ =

volume flowrate

nc =

combustion efficiency

nf =

fuel-conversion efficiency

nm =

mechanical efficiency

noverall =

engine overall efficiency

nt =

thermal efficiency

nv =

volumetric efficiency

Wp =

pumping work

m˙a =

air mass flowrate

bP =

brake power

bT =

brake torque

cc =

cm3

ρa,o =

air density

Acronyms

ABDC =

after bottom dead centre

BBDC =

before bottom dead centre

BSFC =

brake-specific fuel consumption

CFD =

computational fluid dynamics [34,35]

CSRV =

coated spherical rotary valve

IRV =

independent rotary valve

IVC =

intake valve closing

LOTUS =

engine simulation Software

TPFE =

poly tetra fluoro ethylene

VVA =

variable valve actuation

VVT =

variable valve timing

WOT =

wide open throttle

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