Design, Modeling, and Feasibility Analysis of Rotary Valve for Internal Combustion Engine

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Literature Review and Introduction
Recent advancements in design of internal combustion engines have made a lot of progress towards improvement in thermal and mechanical efciencies of the engine as well as resulting in higher mileage and range of the vehicle.Valve design has evolved over the decades due to constant demand of highly efcient and high-power automobiles with 6+ cylinders.Te valve opening area and timing are some of the most critical parameters to achieve high efciency.Te transverse rotary valve is the most direct conversion to the original piston internal combustion engine due to the structural similarity to the conventional poppet valve confguration.Tis section will demonstrate the research progress that has been reported in the literature, followed by the challenges facing the conventional poppet valve design and the advantages of rotary valve design.
Chow, Watson, and Wallis have conducted a study about combustion in a high-speed rotary valve spark-ignition engine.In this research, they designed the combustion model that can simulate a combustion performance for a transverse rotary valve engine with up to 18000 revolutions per minute (rpm) of engine speed.Te experiment data indicate the paths to engine combustion process improvements.According to their study, engine power output increases with volumetric efciency and in-cylinder velocity, with respect to RPM, contributes to the engine power output with its increase [1].Bishop Innovations published their work in 2007 with a dual port single rotary valve design.In their research, a string of timing gears was applied to replace timing chain/belt to transfer the power from the crankshaft to the rotary valve.Integrating both intake and exhaust ports into a single column-shaped valve body, the Bishop rotary valve maximizes the port size and occupies most space above the cylinder for gas exchange.Te rotational motion removes the inertia from the conventional reciprocating poppet valve.To form a proper seal, similar to a piston ring, a seal sits around the rotary valve vent and is slightly preloaded to push against the contacting surface.Te developer states a 16 kg weight reduction with their rotary valve when building a 3-liter V10 F1 engine comparing to the engine that has the poppet valve.Te research also indicated that performance remains the same with their rotary conversion and the peak volumetric efciency is the same as well.Te dual port single valve was successful on F1 racing cars from 1995 to 2005 in reaching 20000 to 24000 rpm [1].
In 2015, Boretti and Scalzo optimized the pneumatic poppet valve.In the study, they also designed a rotary valve which provides ultrasharp valve opening and closing.According to the research, a rotary valve has its capacity to improve the volumetric efciency by providing the largest valve area in a short time.Teir experiment sets the compression ratio up to 14 : 1. Te achievement of their rotary valve includes higher power density, better engine breathing properties, higher fuel conversion efciency, and weight reduction [2].Boretti's other research also indicated that rotary valve could provide a chance for the engine to gain a higher compression ratio.Te study included Bishop Innovations' achievement that solved gas sealing, oil sealing, excessive friction, and seizure caused by thermal and mechanical distortion.Te research also indicated that the gas fow will be diferent from the poppet valve engine due to the lack of piston top valve clearance pockets.Muroki et al. published their work in 1999 focusing on the fow dynamic and the friction efect.Te study proves that rotary valve can save up to 40 percent on valve driving mechanical loss.However, the notch profle in the early stage of the intake stroke would afect the intake fow [3].Muzakkir et al. also conducted a study in 2015 with a hypothesized erect rotary valve that works with a magneto-rheological fuid instead of a solid metal valve seat to form a proper seal and prevent wearing out.However, none has fabricated and tested this confguration of rotary valve [4].
Brown et al. introduced a set of foating valve seal system, in which the spring will push the foating valve seal against the rotary valve to form a seal and self-adjusts to accommodate the wearing out.In the study, the rotary valve was ftted to the high-speed pneumatic machine [5].In 2014, Zibani et al. designed, tested, and implemented a rotary valve control unit for a single-cylinder engine.Te study addressed problems of the conventional valve-equipped engine, such as piston-valve interference and the complexities of the poppet valvetrain.Tey proposed a softwareoperated electronically controlled rotary valve (ECRV) which manages the system and ofers fully fexible valve event control.According to the study, the throttle body can be eliminated to reduce pumping loss.Since the engine control unit successfully operated the experimental system, the idea of extending the electronically controlled rotary valve into a multicylinder engine was shown feasible.Te feature of the electric rotary valve also provides the possibility for variable timing control [6].An analysis presented by Tsu showed an operation with intake and exhaust valve overlap.He implemented a program based on the mathematical modeling to estimate engine performance.Te predicted results ftted mostly well to the experimental data that were collected from three diferent engine examples [7].
Teobald et al. ftted a new programmable electromagnetic valve actuator on a single-cylinder research engine to explore efciency and emission improvements with variable valve actuation operation.Research only shows a net-efciency gain under certain condition.However, actuator's electrical input energy loss was less than the friction loss for a conventional valvetrain [8].In 2017, Stone et al. ftted an electric motor actuated valvetrain on a Jaguar Land Rover 4-cylinder engine and was able to gain up to 7.5 percent of fuel economy improvement.Te study also confrmed throttleless operation feasibility [9].In 2019, Myers introduced a novel engine head design with a new rotary valve system.Te study indicates the new design helps volumetric efciency and cylinder fow.With the new design, the combustion process takes place more evenly and consistently.Te disk shape valve rotor design does not provide any mechanical sealing ability and requires two radial seals which mimic the side seals in a Wankel engine.However, Wankel engine side seal was not an optimum solution to its own.Te valve rotors are interconnected; hence, there is limitation in variable valve timing [10].
Mu et al. published their research in 2022 about improving engine thermal efciency.According to the experiment, the research engine DAM16N achieves its minimum fuel consumption when the engine is running between 2000 and 2800 rpm [11].In 2015, Kopac and Kokturk observed the optimum engine speed.Teir study presented both experimental measurements and analytical modeling throughout a wide range of engine speed.2580 rpm was found to be the best running point for the specifc engine [12].

Benchmark Engine Model.
In this research, an engine from a 1996 SUZUKI DR200 motorcycle that is 4-stroke, spark-ignited, timing chain driven dual-overhead-camshaft, and gasoline fuel powered was selected as the benchmark which provides the base data for all parameters.Te improvements are also developed and compared based on the selected engine structure.

Shortcomings in Conventional
Valvetrain.In order to accomplish gas exchange throughout the entire process combustion, the engine has to have a series of intake and exhaust valve movements based on a timing setup.Conventionally, the valves are driven by the engine crankshaft with a series of mechanical transition systems.Te entire system between the crankshaft and the valve is called the valvetrain.On the mass produced engines, the valvetrain can be classifed into two basic categories which are pushrod driving and belt driving, while in the belt driving category, 2 Journal of Combustion timing belt and timing chain are applied for diferent demands.Tere have been several challenges identifed in the literature for the conventional valvetrain such as inertia, friction, timing, and duration.Tese challenges are explained in detail as follows [13].

Valve Interference
Based on the operation of a four-stroke engine, calculation shows that at 4000 revolutions per minute (RPM), a valve will open 2000 times every minute which converts to 33 times a second.Due to the inertia, a heavy valvetrain will keep its motion further until valve spring catches it.
Eventually, under higher RPM, the valve and its components will be struck too far to be caught by the valve spring in time.
According to Trzesniowski, conventional valve springs are capable to support up to 16000 rpm without causing valve foating.However, such a system requires a much complex valvetrain concept [15].

Power Consumption.
Usually, varying between diferent engines and valvetrain confgurations, the valvetrain contributes up to 25 percent of the total internal friction.Tis percentage reduces with the increase in engine speed.For example, in the study of valvetrain friction [16], the members of Automobili Lamborghini, Calabretta, and Cacciatore introduced that based on motored strip measurements, valvetrain contributes 35 percent of total engine components' friction at 1000 rpm which is close to the engine speed range of crawling in slow trafc and cursing on highway [14].
Tis percentage can be very signifcant especially if the valve spring needs to fght harder to eliminate valve foating in high performance engines.Youd identifes better valve spring dynamic performance with higher internal stresses [17] Valve foating is mainly caused by resonances in the valve springs.To solve this, up to two additional springs can be sleeved up inside of one other.A ribbon damper is also an alternative.However, according to Youd's research, dampers can generate heat and will lead to much higher power consumption [17].

Valve Timing, Lift, and Duration.
Te conventional valvetrain, either driven by the pushrod or the belt, has to have a valve actuator known as the camshaft.Figure 1 shows the structure of the camshaft.On the camshaft, for each valve, there is a cam lobe designed following the specifcation of the valve opening duration, lift, and timing.In other words, the valve motion is preset and controlled by the shape, height, and angle of the cam lobe.However, in order to accommodate diferent working conditions and achieve the optimum efciency, the valve timing, lift, and duration need to have a considerable amount of variation range [13].
To relatively widen the optimum efciency range, auto manufactures and researchers sought various routes on modifying the very basic conventional valvetrain.Fluid actuated valve systems were quite popular in late 1990s and early 2000s.Renault and Aprilia both created the pneumatic valve actuator system to increase valve opening speed and closing force.Renault later also created an electric hydraulic valve actuation system that allows for more advanced valve timing [19].
However, rarely any fuid valve actuation system made to the market.More popularly, manufactures prefer the desmodromic valve actuating system.Tey are indeed more reliable and however introduce even more mechanical parts.
Hence, a novel valvetrain, electronic rotary valve, was created to eliminate the potential of the valve foating and the valvetrain friction by changing the motion type of the valve and reducing the amount of components driven by the crank shaft.Ultimately, cooperating with wider range of variation, the improvement of the engine efciency should be achieved overall during the entire power band.Te advantages of a rotary valve over a conventional poppet valve have been reported in research [20][21][22] and can be summarized as (1) elimination of reciprocating valve motion can result in reducing frictional power losses of the engine.(2) Optimized combustion chambers can be designed using a rotary valve that will provide high discharge coefcient maximizing the airfow in the combustion chamber.(3) Rotary valve can have larger cross-sectional area for an equivalent sized poppet valve.(4) Increased engine power and reduction in fuel consumption can be achieved by eliminating preignition conditions seen in conventional poppet valve.( 5) Fewer moving parts in the rotary valve design would result in the reduced costs of manufacturing and maintenance.
Te new valve will be ftted into the original spaces for the conventional valve.Driven by the overhead electric motor, the valve spins in place to open and close by staggering the vents in the side.Figure 2 shows the novel rotary valve assembly confguration.On the selected benchmark engine, the intake valve opens at exact TDC and then closes at 207 °after BDC.Te exhaust valve opens at 201 °before BDC and then closes at exact TDC.

Camshaft Related Parameter.
Lift and duration are the most primary parameters of the camshaft, which determine how high and how long the valve lifts during the operation of the engine.Figure 4 shows the diagram of the camshaft cross section.(1)

Cam Lobe
Here, l stands for the valve lift, while l l and r a represent the lobe lift and the rocker arm ratio.
On the benchmark engine, the camshaft lobe's maximum sizes are 1.341 in.(intake) and 1.27 in.(exhaust) and the lifts are thus 0.241 in.(intake) and 0.227 in.(exhaust).Te measured magnifcations for both rock arms are 1.335.Te intake and the exhaust valve lifts are 0.322 in.(intake) and 0.303 in.(exhaust), respectively [14].

Valve Opening Area.
Te valve opening area is determined as the curtain area by multiplying the valve lift and the circumference of the valve head, within the critical condition.According to measurements of the original poppet valves, the valve head diameters for the intake and exhaust are 1.3 inches and 1.1 inches, respectively.Consequently, the valve opening areas for the intake and exhaust valves are 1.314 square inches and 1.047 square inches, respectively.While when the curtain area is equal to the valve port area, the valve opening area is considered as the port area.
3.5.Duration.Te duration of valve opening is determined by the period the valve remains open, and it is measured in the crankshaft angle.Tis duration is assessed from when the valve is lifted 0.050 inches to when it is 0.050 inches away from complete closure.In this particular scenario, the intake valve duration is 207 °, while the exhaust valve duration is 201 °.To ensure a smooth rotation of the camshaft lobe and proper valve operation, a transition from the base circle to the maximum lift height is essential.Consequently, the valve's motion is gradual, especially at the beginning and end of its movement.Tis study concentrates on the performance of the intake valve, so only the intake side will be examined.Figure 5 illustrates the measured valve lift curve, indicating a maximum valve lift of 0.322 inches for the intake valve, aligning with the calculated results.

Requirements of the New Valve Design.
To prove that a new design is signifcant, at least the original valve performance has to be met.Under this circumstance, the gas exchange capacity is the key factor of the performance.In other words, matching design of the gas exchange capacity becomes the goal of the research.
Te rotary valve ofers a notable advantage by delivering a sharp and linear valve motion curve.While the physical port of the valve may not reach its original area, the primary goal of valve improvement extends beyond the emphasis on the valve opening area.Te true objective is to enhance the quantity of air aspirated into the cylinder, a factor intricately linked to volumetric efciency.
In contrast to the traditional valve motion, where attention is typically confned to the efective valve lifting range, a more comprehensive approach considers the entire span from the initiation to the culmination of the valve motion.Tis broader perspective encompasses the entire mass of air exchanged by the valve.Unlike the conventional valve, which experiences a wasteful duration during the inefective valve lifting range due to its smooth transition, the rotary valve is specifcally designed to facilitate a sharp and precise valve opening and closing.Consequently, the smooth transition characteristic is eliminated in the rotary valve design.

Design Details
4.1.Timing and Duration.Ultimately, the new design has the ability to achieve unlimited timing and duration variation.However, in this research, since the goal was set to match design on the benchmark engine, the timing and duration settings remain as the original engine measurement.

Lift and Valve Opening Area.
Te rotary valve operates on engine speed-related rotational stagger motion, so the term lift is no longer applicable.However, the shape of the opening port does contribute to performance variation.Tus, the lift can be replaced as opening and closing duration which describes the speed of valve operation.
As discussed, one feature that the rotary valve provides is the sharp valve motion curve which can be translated into fast valve motion.Te feature provides the engine a wider range of efective gas exchange duration.

Valve Shape.
In order to accommodate the original Suzuki engine cylinder head, the valves have to ft into the space of 1.386 × 1.386 × 2.2 inches for the intake valve, respectively.Te optimum shape of the valve application is hemisphere which evenly distributes the force between the valve body and its housing under the combustion cycle.Limited by the size of the space, however, the valves are fnalized into a cone shape with curved surface to prevent self-seizing under heavy load.
On this typical design, the opening ports are made into true circles with three diferent sizes to accommodate the shape of the valve.Te sizes are set to 0.119, 0.148, and 0.165 inches' radius.
4.4.Driving Mechanism.Instead of using the traditional timing components, the rotary valve is driven by the overhead steeper motor.With timing trigger wheel mounted on the crankshaft and correlated crankshaft position sensor, the engine control unit will be able to sense the exact angle of the crankshaft and trigger the steeper motor to drive the valve accordingly to time the motion.

Method.
In order to identify the improvement of the performance on the new valve design over the conventional valve, several parameters can be applied as the measurement.In this research, the shape of the valve body and its port are modifed and hence the motion type.One major change that resulted is the volumetric efciency.On the internal combustion engine, higher volumetric efciency allows the air to fow easier.In other words, the cylinder is able to aspirate more air within the same crank rotation angle.
Since the major change of the structure is the valve shape and motion type, the most direct result will be the change of the valve opening area curve.Tus, in this research, instead of focusing on the overall volumetric efciency table, the individual efciency curve for one cycle of the valve motion will be presented.Comparing this curve between the new design and the conventional design, one can easily identify the diference of the performance.

Program Design.
Volumetric efciency is the ratio of the actual aspirated air volume and the physical cylinder volume.
where V a stands for the actual volume of intake air, while V d represents the theoretical volume of the cylinder [25].Te benchmark engine is an indirect-fuel-injection engine.However, since the amount of fuel is small enough compared with the amount of air, the fuel mass can be neglected for volumetric efciency calculation [26].
In equation ( 3), the actual intake air volume can be presented as the function of air mass and air density.
On the engine dynamometer, air mass is usually replaced by the intake air mass fow rate [26].
where N e stands for engine speed and n r is the number of crankshaft rotations for a complete engine cycle.Intake air pressure and temperature are usually measured in the intake manifold, so the intake air density can be calculated as the following equation: where ρ a is intake air density, P a is intake air pressure, T a is intake air temperature, and R a is gas constant for dry air.Replacing 4 and 5 in 3 gives the volumetric efciency equal with the following equation: In this research, the major change of the improved design as compared to the benchmark engine is the valve shape and its motion type.As the result, the valve fow and discharge coefcients are the most essential efects of the volumetric efciency.Tus, only the intake performance will be evaluated [27].
Te mass fow rate through a valve is usually described by the equation of compressible fow going through a fow restriction.
where P o and ρ o stand for upstream stagnation pressure and density, respectively.c o � ���� � kRT o  stands for sound speed with T o standing for temperature.A E is the efective area of the valve assembly.P T represents downstream static pressure [28].
For fowing into the cylinder, P o and P T are the intake system pressure and the cylinder pressure, respectively.
Introducing equation ( 7) into equation ( 6) and keeping the valve opening area A E as the variable, the relationship between the valve opening area and the instant volumetric efciency can be described.

Valve Opening Area.
Figure 6 shows the design of the rotary valve.In the new design, linear motion no longer exists and hence the curtain shape opening port.Te valve has three diferently sized round ports in every 90 degrees.Driven by the electric motor, for every 45 degrees of rotation, the valve completes its opening and closing.In order to perform a proper curve of the opening area change, the three ports in a roll have to open and close at the exact same time.
In order to calculate the efective valve opening area and present the motion curve, the system can be simplifed into the area problem of a line sweeping across a circle as shown in Figure 7.In this case, the valve opening area can be described as the sum of the truncated circle areas.
where r stands for valve port radius.Since the valve housing and core both have the same size port, the efective valve opening area should be twice as the circular section area.
d o , in equation ( 8), represents the linear distance traveled by the valve ports.A 01 , A 02 , and A 03 represent the A 0 of the 3 port holes, respectively.In this research, since the variable valve algorism is not introduced, the valve motion and the crankshaft rotation angle are still considered as related.
where v v and R represent the valve rotation speed and radius of the valve port orbital.
To complete the comparison between the new design and the old design, the same curve of the conventional valve is needed too.
Based on the valve shape and its motion type, poppet valve has a circular cap that moves up and down to modulate the valve opening and closing.During the valve opening, the edge of the circular valve draws a cylindrical curtain shape and the area of the curtain is the instantaneous valve area [25].

6
Journal of Combustion where d v and l represent the valve diameter and the valve lift.Both parameters are obtained from the actual measurement.By applying the data points of valve lift to the method of polynomial approximation, the valve lift to the function of crankshaft angle can be obtained.Tables 1 and 2 show the coefcients of the 14-degree and 15-degree polynomial approximation.

Saturation Point.
At somewhere in the midrange of the valve lift, the saturation point of the port will be achieved.After this point, the valve curtain area goes beyond the size of the valve seat area and the fow restriction moves from the valve curtain to the actual port itself.At this point, the valve opening area becomes the valve seat area.

Discharge and Flow
Coefcient.Te efective valve opening area defnes the mass fow rate though the valve, which is the product of the reference valve area and the valve discharge or fow coefcient.
For the conventional valve structure, the discharge coefcient will be applied if the reference valve area is set to be the curtain area.Otherwise, the fow coefcient becomes applicable if the reference valve area is the seat area.In this research, the fow coefcient was adopted through polynomial approximation of GT-power simulation [25].
While on the new rotary valve design, since the valve opening area is determined only by the opening condition, equation ( 9), critical condition is no longer necessary to be considered.We only need to determine the fow coefcient.
Te conventional numerical simulated equations are no longer applicable.However, since the structure of the valve opening ports is shaped into circles, the equations of the nozzle and orifce fow coefcient become suitable for this application.
Te nozzle or orifce was used to reduce pressure.In this case, however, it became the restriction of the air fow.
Referencing the physical design of the rotary valve, the device type can be identifed as "orifce, corner taps."Te discharge coefcient is defned as the above equation, where C ∞ stands for the discharge coefcient at infnite Reynolds number, β stands for the area ratio, R e stands for the Reynolds number, and b and n are the coefcients found in the chart from reference [29].
C ∞ � 0.5959 + 0.0312β 2.1 − 0.184β 6 , b � 91.70β 2.5 , n � 0.75.(15) .Results and Discussion 6.1.Valve Opening Size.Since the conventional poppet valve operates related to the camshaft rotation angle, the valve opening area curve should remain invariable under any engine speed.Figure 8 shows the intake valve opening area curve of the poppet valve.
However, the rotary valve is designed to be driven by the electric motor under the motor's constant speed.Once the valve completes its opening operation, the motor will stop and keep the valve remaining opened and then drive the valve close per command of the engine control unit.Limited by the size, it is expected that the new valve design provides a smaller opening area.Nevertheless, the valve opening duration will be increased.Figure 9 shows the valve opening area curve of the rotary valve in three dimensions.According to the calculation, the maximum opening area for the rotary valve and the poppet valve are 0.795 sq.in and 1.315 sq.in.Since the valve operation speed remains constant, with the engine speed increasing, it is obvious that the maximum valve opening area duration reduces.Eventually, the electric motor will not be able to catch up with the engine speed and the valve will not be able to reach its maximum opening area.

Volumetric Efciency.
Instead of focusing on the overall valve assembly efciency, this research went in more detail and calculated the instantaneous efciency during the valve opening process.
Limited by the motion type and cam lobe profle, the conventional poppet valve has to open and close gradually before reaching the maximum efciency.In another words, during the beginning and the end of the motion, the valve has to run under a very inefcient condition and can barely aspirate any air.Furthermore, due to the fxed timing system, the poppet valve can only remain in its higher efciency for a relatively narrow range.However, on the rotary valve design, depending on how quick the valve motor operates, the rotary valve may be able to complete its maximum area opening within a smaller crankshaft angle interval.Figure 10 shows both the instant efciency curve of the poppet valve and the rotary valve at the engine speed of 2900 rpm.
However, due to the performance limitation of the valve driving motor, the valve may not be able to reach its maximum efciency.With the engine speed increasing, the time interval of the intake stroke reduces.Since the valve driving motor operates under its specifed speed, the engine control unit may have to command the valve to start to close before the maximum opening area completes.According to the calculation, the rotary valve design and the conventional poppet valve design will achieve very similar performance at 4400 rpm.Ten, after 4500 rpm, the poppet valve performance exceeds.Figure 11 shows the efciency curve at 4400 rpm.Aspirated air volume ratios between the popped valve and the rotary valve are 0.850 and 0.996 at 2900 rpm and 4400 rpm, respectively.
As mentioned earlier, the maximum opening area for the rotary valve was calculated to be 0.795 sq.in which was smaller than the poppet valve's area of 1.315 sq.in.However, under 2900 rpm engine speed, the rotary valve was able to remain fully opened with constant efciency of about 54%  from 40 to 160 degrees of the crankshaft angle.While the poppet valve can achieve 88% efciency at 90 degrees of the crankshaft angle, the efciency signifcantly drops on either sides of the maxima.

Conclusion
Based on the modeling, simulation, and design of experiments, the authors have distinguished the advantages and the limitations of the newly proposed rotary valve design.Tis design enables maximum opening of the valve for longer duration and hence has the potential to enhance efciency of the engine.However, in this research, limited by the space, the new design that was constructed based on the existing engine head could not compete on the maximum opening area with the conventional design.
Modifcations that make horsepower and torque in the lower rpm range between 1500 and 3000 rpm are way more useful than a high-revving race motor, and most modern civilians use vehicles running at 2000-3000 rpm when cruising at a speed of 70 mph.Literature review also showed that engines obtain their optimum efciency at lower engine speed.In this research, the authors found that the proposed rotary valve design provides a constant efciency of 54% for much larger crankshaft angle duration as compared to the conventional poppet valve design under 2900 rpm engine speed.
Based on the calculations, the rotary valve design can achieve better performance below 4500 rpm, and it will contribute towards reduction of the engine internal friction by eliminating the entire valve driving mechanism.Comparing to other rotary valve designs, the proposed design in this study ofers a shape that is naturally mechanically sealed.Te intake and the exhaust side valves are independent.Electronic control concept ofers a fast opening speed and longer duration.Te concept is also signifcant for the future research on the wide-range variable valve timing system and high-compression interference free engine design.

3. 1 .
Valve Opening Timing.According to the timing diagram that is shown in Figure3, timing can be addressed down to the crank shaft angles where the valves open or close.

Figure 8 :Figure 9 :
Figure 8: Intake valve opening area curve for the poppet valve.

Table 1 :
14-degree polynomial approximation coefcients of the poppet valve lift curve.

Table 2 :
15-degree polynomial approximation coefcients of the poppet valve lift curve.