Abstract Introduction

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2018-01-0376

Published 03 Apr 2018

Effects of Variable Intake Valve Timings and Valve Lift on the Performance and Fuel Efficiency of an Internal Combustion Engine Pauras Sawant University of North Carolina Charlotte Saiful Bari University of South Australia Citation: Sawant, P. and Bari, S., “Effects of Variable Intake Valve Timings and Valve Lift on the Performance and Fuel Efficiency of an Internal Combustion Engine,” SAE Technical Paper 2018-01-0376, 2018, doi:10.4271/2018-01-0376.

Abstract

T

o comply with the new Corporate Average Fuel Economy (CAFE) standards, automakers are expected to increase the average fuel economy of their vehicles to 54.5 miles per gallon from the current 24.8 miles per gallon by 2025. This research aims at proposing a feasible solution to narrow down the gap between the current and expected fuel economy of the vehicles, yet maintaining the engine’s original performance. A standard model of the KTM 510 cc single cylinder, fuel injected, internal combustion engine (IC) engine is modelled and simulated in Ricardo Wave software package to map the stock engine performance and specific fuel consumption at wide open throttle (WOT). The baseline simulation model is validated against the experimental readings with 98% accuracy. The intake valve timings (IVO, IVC), valve lift and profile, being major contributors to the

Introduction

T

he current day advancements in the field of IC engines can be broadly classified into two types. The first type aims at increasing the engine performance at the cost of increased fuel consumption. Whereas, the second type of advancements aim at increasing fuel efficiency at the cost of engine performance [1-3]. Keeping in mind that the consumer’s demand of increased performance and the Environmental Pollution Agency’s (EPA) [4] requirements of increased fuel efficiency, this research aims at blending the two types and providing the consumer an engine that will satisfy the need of increased performance when driving on race tracks and save money and fuel with increased fuel efficiency when driving on highway or interstate roads. Engine breathing (charge induction and scavenging) i.e., volumetric efficiency, and the combustion chamber design govern the in-cylinder wave and gas dynamics and is a major contributor to the engine’s overall performance and efficiency [5, 6]. Ensuring optimum performance of the engine would call for a balanced design of all the components in the engine induction assembly. This process is found to be mainly dependent on design parameters like port lengths, port taper, port

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wave and gas dynamics in the combustion chamber are then varied at all engine speeds to capture the amplified induction pressure wave to boost the volumetric and thermal efficiency and attain optimized engine performance. As a combined effect of varying the above parameters, the engine performance (torque and power) is boosted by an average of 6.02 percent throughout the engine’s operating speed range. The improvement in the lower speed range of 3000-4000 rpm is around 18.72% as this KTM is originally tuned for higher speed range of 5500 to 6000 rpm. The addition of variable valve lifts (VVL) to variable valve timings (VVT) further reduces brake specific fuel consumption (BSFC) at all engine speeds with an average reduction of 0.35%. The results show that the not only the performance of the engine can be boosted, but also the fuel efficiency can be increased by a precise control of VVT and VVL induction assembly.

diameter, valve profiles, valve timings and valve lifts [1-5, 7-14]. When a naturally aspirated internal combustion engine has the correct set of all the above-mentioned design parameters to capture the induction pressure waves and ensure optimum gas exchange process, it is said to be tuned for that engine speed. Extensive research is going on in the field of induction systems for IC engines. For an engine with a fixed air induction assembly, the tradeoff between the engine torque and the fuel efficiency is difficult. If the engine performance increases, the fuel efficiency decreases and vice-versa. As, seen in Figures 1 and 2, the engine speed is subject to continuous change depending on the loading conditions and desired vehicle speed. Generally, naturally aspirated engines are tuned only for a single operation speed. However, as much as tuning helps to increase the performance at the speed the engine is tuned for, it may also hurt the performance of the engine at other speeds. This hurdle has deterred the engine designers to design engines to work at their optimum capacity for years. Figure 3 shows a conventional valve time diagram. The conventional engines induction assemblies are usually designed to give balanced performance at all engine speeds


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Effects of Variable Intake Valve Timings and Valve Lift on the Performance

FIGURE 3 Conventional valve timing diagram [15].

© SAE International

FIGURE 1 Typical variation in engine speed with respect to vehicle velocity.


FIGURE 4 Acoustic Resonance [29].

FIGURE 2 Typical variation in engine speed with respect



to time.

rather than being biased to any single engine speed. However, the ideal situation would be to create an induction boost across the engine’s entire operating speed range. This would require an infinitely variable port and valve geometries [10, 13]. This challenge has led the engine manufacturers to explore the possibilities of varying the geometry of multiple components of the engine induction assembly. A few of the possibilities explored are variable runner lengths, variable runner diameter, variable plenum volume, variable runner taper and bellmouths, variable valve lifts, variable valve timings and profile [7-10, 14, 16-26]. Varying the runner diameters, lengths and plenum volume would need a complicated mechanism as compared to varying valve timings and lifts. Mahindra 2 Wheelers [21] and Toyota’s Acoustic Control Induction System (ACIS) [7, 27] are examples where different sets of runner lengths are used for lower and higher engine speeds. Variable runner diameter and variable plenum volume have not been so commonly used owing to the complexity of their manufacturing and integration.

The most commonly implemented strategy is variable valve actuation (VVA). The common mechanisms that have been implemented in production are 2 or 3-step cam phasing for variable intake valve timings followed by cam profile switching for variable intake valve lifts. Honda first introduced a 3-step cam mechanism to adjust valve lifts. Later, they also introduced a cam phasing to their 2-steps to adjust valve timings with respect to engine operation speeds [18]. BMW as well, with their ‘Valvetronic’ technology provides continuously variable valve lift and duration with cam phasing [28]. As discussed earlier, Sammut et al. [9] has also suggested that tuning focusses mainly on capturing the compression and rarefaction pressure wave arising in the intake manifold and are mainly dependent on piston motion and resonance characteristics of the air in the intake manifold [8]. These waves are mainly generated due to the negative pressure in the cylinder during the intake stroke. They are also generated due to the pressure differential between the intake manifold and exhaust manifold during the valve overlap period. The third and the most dominant cause of these pressure waves is the valve closing event. After the intake valve is closed, the column of air still is in a state of inertia and keeps on moving back and forth along the intake runner as a sound wave as seen in Figure 4. The motion of this air column can be compared with the motion of a box after repeatedly colliding on a spring. This wave too © 2018 SAE International. All Rights Reserved.



gains tone and amplitude with every reflection. The method of tuning the engine for capitalizing this pressure wave is also referred to as acoustic supercharging [1, 5, 10]. From the above discussions, it is clear that the design of the induction system of an IC engine is critical to improve the volumetric efficiency which can lead to improve fuel efficiency and/or performance. This research mainly focuses on tuning the valve opening timings alone, and then together with valve lifts to achieve both optimal performance and improve brake specific fuel consumption.

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FIGURE 5 Pressure waves along intake runner [35].

Volumetric efficiency is measured as the ratio of mass of air inducted into the cylinder to the mass of air that can be contained in the cylinder volume [24, 30-32]. In mathematical form:

hv =

mg mg v = = 9 (1) mtn vth * rth vth

Where, ηv - Volumetric efficiency mg - Actual mass of air inducted mtn - Theoretical mass of air that can be contained in cylinder ρth - Density of ambient air v 9 - Volume of air inducted vth - Swept volume When then induction pressure waves are captured, the static pressure differential between the air above the intake valve and vacuum in the cylinder (below the intake valve) increases [33]. This increases the amount of air being inducted during the induction stroke, thereby increasing the volumetric efficiency. With the increase in the mass of air inducted, the oxygen molecules available for combustion of the injected fuel increases. Thus, with the increased oxygen molecules, more fuel can be injected leading to gain in torque and power. Also, the peak cycle temperatures will increase. With the increased peak cycle temperatures and increased turbulence due to increased air-flow, the engine can be run using comparatively leaner mixtures, thus reducing the fuel consumption [1]. This will also lead to better fuel combustion, reducing the CO emissions [22, 34]. Hence boosting the volumetric efficiency will increase power, torque and at the same time also increase the fuel efficiency and reduce CO emissions [25]. However, higher cycle temperature will lead to higher NOX emissions [2]. Appropriate application of the equations to capture the induction pressure waves requires an understanding of the pressure wave phenomenon used for tuning the induction systems. As discussed above and can be seen in Figure 5, air travels as sound wave with undulating pulsations and gain speed, tone and amplitude with every reflection [17]. These pressure waves travel at the speed of 381 to 396 meters per second at intake temperatures of 25 to 30°C. Chrysler’s ram air theory suggests that these pressure waves are formed just above the intake valve and travel up to the plenum where they © 2018 SAE International. All Rights Reserved.


Methodology

are reflected with reversed polarity due to the abrupt change in cross section area of their flow path. These waves return to intake valve and keep travelling back and forth until the valve opens. If the intake valve is opened exactly when the positive pressure wave arrives at the intake valve, it will create a sudden boost in induction pressure thereby increasing the volumetric efficiency of the engine [16, 29]. For the duration when the intake valve is open, the Helmholtz resonator theory considers the intake runners and the cylinder a resonance chamber and suggests that the peak volumetric efficiency will be obtained when the Helmholtz resonance of the runners and the cylinder as a combined system will be twice the piston frequency [36]. The concepts of the ram air theory and Helmholtz resonance theory, have been substantially used to tune the induction systems for over 60 years. Considering the combined effects of the above two theories and the cylinder dynamics, the derivatives of these theories propose the following equation to calculate the length of the intake runners for multiple reflections of the induction pressure waves [5, 17, 26, 36, 37].

æ ( ECD ´ 0.25 ´ C ´ 2 ) ö Leff = ç ÷ - 0.5 D (2) ç ( rpm ´ RV ) ÷ø è Where, Leff - Effective length of runner (m) = (measured length (L) + 0.5 × average runner diameter (D)) C - Speed of sound at intake temperature (m/s) ECD - Effective cam duration (degrees of cam rotation) N - Engine speed (rpm) RV - Number of reflections D - Average runner diameter (m)

As it can be seen in equation 2, the tuned intake runner lengths are a function of engine speed and valve open duration. So, this equation can be re-written as equation 3 to get the same tuning effects by changing the valve timings and profile

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with respect to engine speed and maintaining the intake runner geometry constant.

æ ( rpm ´ RV ´ Leff ) ö ECD = ç - 0.5 D (3) ç ( ECD ´ 0.25 ´ C ´ 2 ) ÷÷ è ø Where, Leff = effective length of runner (m) = (measured length (L) + 0.5 × average runner diameter (D)). C = Speed of sound at intake temperature (m/s). ECD = Effective cam duration (degrees of cam rotation). N = Engine speed (rpm). RV = Number of reflections. D = Average runner diameter (m).

The opening and closing of the intake or the exhaust valves with respect to the piston Top Dead Centre (TDC) and Bottom Dead Centre (BDC) is referred to as valve events. The intake valve is generally opened before the top dead center to optimize air-flow at peak lift to facilitate internal exhaust gas recirculation (EGR). During the valve overlap period, when both the intake and exhaust valves are open, part of exhaust gases can flow into the intake manifold, rather than leaving the cylinder through the exhaust manifold. The resulting internal EGR would cause to dilute the in-coming fresh air, thereby reducing the number of oxygen molecules available for the combustion of fuel. This will decrease in-cylinder maximum cycle pressure and temperature, thereby, reducing NOX emissions. Due to reduced peak cycle temperatures and pressures, comparatively rich mixtures will be required at full load conditions with a wide open throttle to produce the same amount of power, thus reducing the fuel efficiency at full load conditions. However increased EGR, depending on the valve overlap period will also reduce the torque at full load conditions. Hence controlling the valve overlap period according the engine speed is very important to maintain a balance of fuel efficiency and full load torque [1, 22, 38, 39]. Intake valve lift and intake valve closing timing decides the amount of air that can be trapped in the cylinder during the intake stroke. Ideally intake valve should be closed exactly when the maximum amount of air has been captured in the combustion chamber to get the maximum possible torque output. Inertia of the air-column flowing into the cylinder continues to keep filling the cylinder even after the piston has reached BDC until a certain point. Advancing valve closing event before this point will prevent this extra air from entering the cylinder. Whereas retarding the valve event beyond this point will cause the inducted air to flow back into the intake manifold owing to pressure from the upward movement of the cylinder. In both the cases the volumetric efficiency of the engine will reduce hurting the performance and efficiency of the engine. Hence precise control over these pressure waves is very important. The coefficient of flow, kinetic energy and turbulence intensity of the air flowing through the intake valve govern the behavior of the induction wave created during induction stroke. Hence, varying valve lifts according to the engine speed will grant a precise control of the pressure wave and help to boost the volumetric efficiency, torque and thus, the fuel efficiency at all engine speeds [1, 22, 38].

Simulation Case Setup The use of an engine simulation software significantly reduces the time, effort and cost involved in manufacturing and testing the variable induction assembly. This research uses the ISO approved and commercially accepted Ricardo Wave engine simulation software package for modeling the engine performance and analyzing the results. With the user provided data, physics models, pre-programmed equations and governing physics laws of energy, mass, momentum, heat transfer, Ricardo Wave uses various finite difference schemes to simulate engine performance parameters in steady or transient state for virtually any intake, combustion and exhaust system configuration [19, 24, 40, 41]. The 510 cc KTM single cylinder internal combustion engine is a short stroke, high performance, high revving, electronically port injected Spark Ignited (SI) engine that qualified for all the necessary requirement and hence, was selected for this study. The engine specifications are given in Table 1. The engine is tested on an engine dynamometer to record the baseline performance of the engine at its most mid-range operating speeds of 5500 rpm to 7500 rpm. Based on the measured geometric parameters and some data available from the engine service manual, the engine is modelled in Ricardo Wave as can be seen in Figure 6. TABLE 1 Engine specifications [42].

Number of Cylinders

1

Bore

95 mm

Stroke

72 mm

Length of Connecting Rod

122.4 mm

Compression Ratio

11.9:1

Number of Valves

4

Intake

Number of Valves

2

Valve Diameter

40 mm

Valve Lift

9.62 mm

Stock Port Length

460 mm

Length of Variable Section 350 mm Exhaust

Number of Valves

2

Valve Diameter

33 mm

Valve Lift

8.58 mm

Stock Port Length

573 mm

Fuel Delivery

Port Injected

Fuel Type

Indolene

Air/Fuel Ratio Valve Timings

14.7 Intake

Exhaust

Open

13° Before top dead center

Close

72° After bottom dead center

Open

109° After top dead center

Close

36° After top dead center

Heat Transfer Model

Woschni Heat Transfer

Combustion Model

SI Wiebe Combustion © 2018 SAE International. All Rights Reserved.




FIGURE 9 Simulated valve opening time range.


FIGURE 7 Brake Power - Comparison of simulation and experimental results.

The model is altered, and it is assumed that the intake runners has uniform cross-section area to simplify the calculations of values to be simulated. The engine’s simulated performance is matched with the engine’s test performance results from 5500 to 7500 rpm with accuracy of 98% as can be seen in Figures 7 and 8. Also, few extra pressure and temperature sensors are added in the simulation to provide data to analyze the direct causes and effects of the performance improvements.



FIGURE 6 1-D model of engine in Ricardo Wave.

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After the validation of the simulation model, the intake valve opening time is varied from 290 degrees to 374 degrees after bottom dead center (BDC) (70 degrees BTDC to 14 degrees ATDC) to vary the valve overlap time. This wide range of valve opening time would help to analyze the effects of valve events and varying overlap throughout the engine operating speed range. Figure 9 shows the minimum and maximum overlap periods simulated. Where. 0 - Exhaust valve profile. 1 - Most advanced intake valve opening timing. 2 - Baseline intake valve opening event. 3 - Most retarded intake valve opening timing. After getting the best valve opening timings at each engine operating speed to give optimal engine performance, the valve lifts are varied by varying the valve lift multiplier from 0.8 mm to 1.2 mm to determine the valve lifts that can give peak thermal efficiency. Figure 10 shows the range of valve lifts where the engine performance is simulated for each engine speed. FIGURE 10 Simulated valve lift range.



FIGURE 8 Brake Torque - Comparison of simulation and experimental results.



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Where. 0 - Exhaust valve profile. 1 - Least intake valve lift. 2 - Baseline intake valve lift. 3 - Highest intake valve lift.

pressure exerted by the upward motion of the piston past bottom dead center. Both the intake valve opening and closing events would not let the cylinder to be filled to its optimal capacity. Hence the valve timings are advanced at 6500 rpm as can be seen in Figure 12. Figure 12 also shows the induction pressure waves at 6500 rpm for the optimized case. The intake valve opening time is adjusted to capture the peaks of the induction pressure wave and intake valve closing time is adjusted to capture the pressure wave arising due to ram air effect. The pressure waves shown in Figures 11 and 12 will move few degrees to the right as the pressure sensor placed 5 mm away from the intake valve owing to the limitations of the simulation software. Therefore, in Figure 12 the peaks of the pressure waves shown in ‘red’ lines will move few degrees to the right. A similar approach of tuning is used at all the other engine speeds to get the respective optimized valve opening timings. The optimized set of valve opening timings for optimized power and torque output at each engine speed simulated are shown in Figure 13. As it has been discussed earlier, advancing the valve timings at lower engine speeds, would increase the valve

Results & Analysis The simulation models are run from 3000 to 9000 rpm and the performances after the span of every 500 rpm are observed. The effects of varying valve timings alone and then, together with valve lifts are observed on engine’s performance and efficiency. The optimized valve setups to gain max torque and improved BSFC are carried out in two steps. First the intake valve opening timings that would provide maximum volumetric efficiency and torque output at each engine speed are recorded from the simulations. The simulation with optimized variable valve opening timings is referred to as optimized VVT simulation. Further, the valve lifts are varied in the optimized VVT simulation to obtain the valve lift multipliers that would provide the maximum thermal efficiency and reduce the brake specific fuel consumption for each engine speed. The simulation with variable valve timings and variable valve lift multipliers is referred to as optimized VVT + VVL. A pressure sensor is attached 5 mm above the intake valve to measure the static pressure at that point and monitor the pressure waves in the intake runner. The sensor could not be setup above the valve due to software limitation. Depending on the occurrence of the peak amplitude of this pressure waves the valve opening and valve closing events are adjusted to gain the maximum possible boost in induction pressure. Figure 11 shows an example of a pressure wave occurrence at 6500 rpm for the baseline simulation case. The intake valve is opened at 343 degrees (163 degrees ABDC) which is much after the occurrence of the peak of the induction pressure wave. Also, the intake valve is closed at 606 degrees (66 degrees ABDC). It can be seen from Figure 11 that the intake valve is closed after the peak of the induction pressure wave caused due to the ram air effect. This would lead some freshly inducted charge to flow back into the intake manifold due to the


FIGURE 12 Optimized induction pressure wave and valve profile at 6500 rpm.

FIGURE 13 Optimized valve opening timings for all engine speeds.

FIGURE 11 Baseline induction pressure wave and valve



profile at 6500 rpm.




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overlap period and the resulting EGR decreases the volumetric efficiency of the engine as seen in Figure 14. Whereas at higher engine speeds, retarding valve opening timings would reduce internal EGR, filling the entire combustion chamber with increased number of oxygen molecules for complete combustion increasing torque output. Also, retarding the valve closing time would increase the time available for the ram air effect to pump more air into the cylinder even after the piston has moved past the bottom dead center. This will ensure that all the cylinder is filled to its maximum capacity before the intake valve is closed. Precise control of valve timing makes it possible to increase in the induction pressure that leads to an increase in overall volumetric efficiency of the engine at all operating speeds as can be seen in Figure 14. However, Figure 15 shows that with the overall increase in volumetric efficiency, the thermal efficiency of the engine is found to reduce by an average of 2.18% throughout engine operating speed range due to increased fuel consumption to have increased power (as shown later in Figure 17).

This reduction in the thermal efficiency is countered by varying valve lifts with respect to engine operating speeds. Hence, for the case with the optimized valve timings, the valve lifts are varied and optimized to decrease BSFC and increase thermal efficiency. The optimized set of valve lifts to get maximum fuel efficiency are shown in Figure 16. After the addition of variable valve lifts to variable valve timings, the improvements in volumetric efficiency is reduced by an average of 0.8% throughout the mid-range engine speeds as compared to variable valve timings alone [Figure 14]. But, the addition of variable valve lifts caused a considerable rise in the thermal efficiency [Figure 15]. The thermal efficiency increases by an average of 2.42% as compared to optimized VVT simulation and 0.32% as compared to baseline simulation. Figures 17 shows the increase in engine power output. Just as in the case of volumetric efficiency, the improvement in the power and torque output are more in the case of optimized variable valve timings alone than compared to co-existence of the both. The overall power improvement is 6.02% over the speed range, and the peak improvement is around 28.5% at 3500 rpm. The improvement is more in the

FIGURE 14 Comparison of volumetric efficiency.

FIGURE 16 Optimized valve lift multipliers for all



engine speeds.

FIGURE 17 Improvement in engine power.



FIGURE 15 Comparison of thermal efficiency.



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lower speed range (18.71% over the speed range of 30004000 rpm) than the higher speed range as the KTM engine is a high revving engine. The improvement is minimal in the speed range of 5500-6000 rpm (0.05% at 6000 rpm) as the original valve timing has been tuned at around this speed range. Representing the pressure volume diagram on a natural logarithmic scale helps to better accentuate the gas exchange differences in the pumping loop [43]. Due to the increase in induction pressures and resulting increase in volumetric efficiency, the pumping losses go down as can be seen in the lower part of the Pressure-Volume (PV) diagram shown in Figure 18. Figure 18 also shows that the area under the net PV diagram at 3500 rpm for the optimized case has considerably increased. The peak cycle pressure is also increased from 58.56 bar to 72.82 bar. This also justifies the peak increase of 28.5% in brake horse power after appropriate tuning at 3500 rpm as can be seen in Figure 17. Figure 19 shows the increase in brake torque output. It can also be observed from Figures 14 and 19 that optimized


FIGURE 18 Comparison of linear P-V diagram of baseline and optimized case at 3500 rpm.

volumetric efficiency and brake torque followed a similar trend and the peak torque occurs at peak volumetric efficiency. Higher volumetric efficiency means more air can be made available to burn more fuel and produce more torque and power. An increase in volumetric efficiency has also caused an increase in the peak cycle pressure, temperature and thus, turbulence. However, since the engine is still being operated at a constant air-fuel ratio as before, there has been a decrease in thermal efficiency as seen in Figure 15 [1, 5]. As a result, as can be seen in Figure 20, the brake specific fuel consumption increases with increase in performance due to variable valve opening timings alone. However, with the addition of variable valve lifts more effective control over the pressure wave characteristics and in-cylinder gas dynamics like the coefficient of flow, kinetic energy and turbulence intensity is achieved [22, 38]. As a result, tuning the valve lifts for every engine speed, decreases the brake specific fuel consumption by an average of 0.35%, thus reducing the fuel consumption at all engine operating speeds. The power [Figure 17] and torque [Figure 19] performance improvements resulting from the improvements in volumetric efficiency [Figure 14] have been summarized in Figure 21. The average improvement is 6.02% with 28.5% improvement at 3500 rpm. The reduction in BSFC (Figure 20) resulting from improvements in thermal efficiency (Figure 15) have been presented in Figure 22. Figures 17, 19 and 22 suggest that appropriate balanced adjustments in valve opening timings and valve lifts can enhance the engine performance as well as improve the fuel efficiency of the engine. It has also been observed that the net increase in performance of the engine around 5500 rpm - 6000 rpm is almost negligible. This suggests that the original intake valve has been tuned to produce peak performance around this engine speed. Also, the decrease in brake specific fuel consumption of the engine around 4000 rpm is negligible. This suggests that the original

FIGURE 20 Improvement in brake specific



fuel consumption.

FIGURE 19 Improvement in engine torque.





FIGURE 21 Improvement in engine performance.

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It is observed that precise tuning can considerably improve the engine performance and efficiency. Engine brake torque and brake power output are significantly improved due to the induction pressure boost created by variable valve opening events, buts hurts the fuel efficiency of the engine. As an effect of varying valve lifts in addition to variable valve timings, the fuel efficiency is considerably increased with a slight loss in the gains obtained in engine performance due to variable valve timings alone. An appropriate selection of valve opening events and valve lifts enhanced the performance (torque and power) of the engine by an average of 6.02% throughout the entire operating speed range with a peak improvement of 28.5% at 3500 rpm and least improvement of 0.05% at 6000 rpm. Also, an average reduction of 0.35% in brake specific fuel consumption is observed with peak reduction of 1.35% at 3500 rpm and minimum reduction of 0.05% at 4000 rpm.

References FIGURE 22 Percentage reduction in BSFC.

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engine has valve lifts tuned to deliver most fuel-efficient performance at this engine speed, which is also the most typical cruising speed for this engine. However, the stock fixed induction assembly is harming the performance and efficiency of the engine at other speeds, which will not be the case with the new optimized variable valve timing and variable lift induction assembly.

Conclusions The effects of tuning intake valve event and intake valve lift are successfully studied, simulated, observed, and analyzed. © 2018 SAE International. All Rights Reserved.

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Definitions/Abbreviations ABDC - After Bottom Dead Centre ATDC - After Top Dead Centre BDC - Bottom Dead Centre CAFE - Corporate Average Fuel Economy

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EGR - Exhaust Gas Recirculation IC - Internal Combustion TDC - Top Dead Centre VVT - Variable Valve Timing VVL - Variable Valve Lift

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