Variable Valve Actuation System Research Articles

Performance evaluation of linear variable valve actuation for a linear engine generator

The Joule cycle Linear Engine Generator (LEG) is a promising power generation technology with the potential to achieve zero carbon emissions. However, the LEG expander valve actuation system presents unique challenges due to its lack of a traditional crankshaft, the need for swift valve lift and reversal, and variable lift. This paper presents a Linear Variable Valve Actuation (LVVA) system for a LEG prototype. The LVVA system is powered by voice coil motors. Rigorous experimental investigations were conducted to analyze crucial performance factors, including energy consumption, force balance, energy flow distribution, and the relationship between valve lift duration and energy consumption. The results show that the LVVA system can achieve the desired valve lift and timing, as well as very small variations in LEG performance compared to the model using an ideal lift curve. The LVVA accounts for approximately 3.59 % of the LEG power output. The energy consumption of 1.607 J per valve stroke provides a slight advantage over traditional actuation systems. The obtained optimal lift curves were used to refine the LEG model. The influence of valve lift curves on LEG performance was evaluated which reveals rapid valve openings and relatively short duration contributing to improved LEG performance.

Intake Valve Profile Optimization for a Piston-Type Expander Based on Load

Intake valve parameters significantly affect the performance of the piston-type expander (PTE). To improve compressed energy utilization efficiency, intake valve parameters need to be regulated according to load. In this paper, an electro-pneumatic variable valve actuation (EPVVA) system was proposed for independent control distributing valve parameters. The trajectory planning for the intake valve was proposed to obtain good mechanical properties. Then, the intake valve duration angle was optimized, and the optimum intake valve lift curves were obtained at different rotational speeds. Results show that the energy efficiency decreased with the intake valve duration angle increasing. The output power ascended sharply with increasing intake valve duration angle, but the amplitude of power growth decreased. The output power had a maximum value at a specific intake valve duration angle. The gray relation analysis (GRA) method was applied to obtain the optimum intake duration angle based on output power and energy efficiency. Finally, the optimum intake valve trajectories were presented under different rotational speeds. Results are helpful for the future control of the piston-type expander.

Valve Motion Characteristics and Application on Engine Based on a New Variable Valve Actuation System

Valve Motion Characteristics and Application on Engine Based on a New Variable Valve Actuation System

A comparative assessment of performance, combustion, and emissions of a gasoline port and direct injection camless engine

AbstractThe lower part‐load efficiency of the spark‐ignition (SI) engine is because of the higher pumping loss during the gas exchange process. In this study, the part‐load efficiency of a port fuel injection (PFI) and gasoline direct injection (GDI) camless engines were investigated. An in‐house developed electro‐pneumatic variable valve actuation (VVA) system controls the camless engine's intake valve events. The effect of un‐throttled operation with early intake valve closings (EIVC) on performance, combustion, and emissions was analyzed. The IVC timing for GDI camless engine was found to be lower (2°–7° crank angle) than the PFI camless engine for all operating conditions due to the in‐cylinder charge cooling. Hence, the pumping mean effective pressure (PMEP) for GDI camless engine was reduced, and brake specific fuel consumption (BSFC) was improved (maximum 2.1%) compared to the PFI camless engine. The THC and CO emissions were higher for GDI camless engine due to the relatively in‐homogeneous mixture formation, whereas the NOx emission was lower for all operating conditions.

Performance Optimization Using ANN-SA Approach for VVA System in Diesel Engine

<div class="section abstract"><div class="htmlview paragraph">Diesel engine is vital in the industry for its characteristics of low fuel consumption, high-torque, reliability, and durability. Existing diesel engine technology has reached the upper limit. It is difficult to break through the fuel consumption and emission of diesel engines. VVA (Variable Valve Actuation) is a new technology in the field of the diesel engines. In this paper, GT-Suite and ANN (artificial neural network) model are established based on engine experimental data and DoE simulation results. By inputting Intake Valve Opening crake angle (IVO), Intake Valve Angle Multiplier (IVAM) and Exhaust Valve Angle Multiplier (EVAM) into the ANN Model, and by using SA (simulated annealing algorithm), the optimized results of intake and exhaust valve lift under the target conditions are obtained. According to the optimized results, the fuel consumption of BSFC (brake specific fuel consumption) can be saved by 3.9%, 0.9%, and 7.3% at three different target working conditions, respectively (1000r/min with 50% load, 2000 r/min with 35% load, and 3000r/min with 20% load. Under the three conditions, the intake valve lifts are 1.10, 0.96, 1.10 times as the original respectively and the exhaust valve lifts are 0.98,0.94 and 1.10 times respectively. In addition, by adding the secondary opening strategy of the exhaust valve lift, internal exhaust gas recycling (IEGR) can be achieved. The exhaust gas temperature increased by 9.55% (66.64K) under low-speed working condition, and fuel consumption increased slightly by 6.15%, which is also important for exhaust thermal management and external emission control in the cold start phase of diesel engines. By changing the intake and exhaust valve control, there are obvious differences in the optimal valve lift under different working conditions. Therefore, the application of the VVA system in the diesel engine is of great significance.</div></div>

Effect of internal exhaust gas recirculation on performance, combustion, and emissions in a PFI camless engine

AbstractThe internal exhaust gas recirculation (EGR) into the intake manifold has a significant impact on fuel economy and emissions in the spark ignition (SI) engine. In this study, an in‐house developed novel electro‐pneumatic variable valve actuation (VVA) system was integrated on a PFI conventional engine and modified into PFI camless engine to vary the valve events independently. The potential of the developed VVA system in achieving the internal EGR by varying the intake valve opening (IVO) timings was widely investigated. The IVO timing was varied from 30° CA (crank angle) bITDC (before intake top dead center) to 40° CA aITDC (after intake top dead center). The spark timing was varied from 10° to 30° CA bCTDC (before compression top dead center). A 41% pumping mean effective pressure reduction was achieved with varying the IVO from 40° to −30° CA aITDC. It is due to the internal exhaust gas recirculation into the intake manifold that reduces the differential pressure between the manifold and combustion chamber. The entrapment of exhaust gas in the intake manifold dilutes the fresh charge, which deteriorates the combustion. However, advancing the spark timing from 10° to 30° CA bCTDC at IVO −30° CA aITDC, an 18% gas excahnge efficiency improvement was obtained. The fresh charge dilution forms an inhomogeneous mixture inside the cylinder that results in lower NOx emission. It is concluded that the developed VVA system has the potential to improve part loads efficiency by utilizing the internal EGR in a PFI camless engine.

A methodology to study the interaction between variable valve actuation and exhaust gas recirculation systems for spark-ignition engines from combustion perspective

Several technologies are being put in place to improve the efficiency of spark-ignition engines. Two of these technologies are variable valve actuation and exhaust gas recirculation, both of which can have an impact on combustion according to the literature. However, this impact is due to variations in both the in-cylinder temperature and composition, linked to the different characteristics of internal and external residuals, which are difficult to decouple. In this paper, a methodology aimed at improving the understanding of the temperature and composition effects on combustion parameters is developed. Internal residuals are controlled through a variable valve timing actuation, and evaluated thanks to a previously validated one-dimensional engine model, while the externally-circulated exhaust are extracted after the catalyst through a low-pressure system. Combustion is analyzed based on in-cylinder pressure acquisition and emissions measurement at the engine-out, before the aftertreatment module. Different combinations of internal and external residuals are tested with different strategies from the point of view of the spark actuation: first, a constant spark timing for each value of total residuals; then, a spark timing adapted to maintain the same temperature inside the cylinder at the combustion start, and finally an optimized calibration from the point of view of the engine efficiency. Results show a general trend to enhance combustion timings as higher share of internal residuals are introduced for the same amount of total residuals. It can be seen how this trend comes mostly from the temperature effect at low total residuals fraction, while composition effects are more significant as the amount of total residuals increase. Empirical correlations developed in the paper confirm the need to decouple internal and external residuals to have a proper estimation of the combustion timings. Despite the positive impact of internal residuals on the combustion duration, a small fuel consumption benefit is reached with cooled exhaust gas recirculation thanks to lower heat transfer losses. In terms of emissions, unburned hydrocarbon emissions tend to be reduced with increasing the share of internal residuals thanks to the higher combustion speed, while other gaseous emissions are mostly affected by the total residuals amount. Therefore, internal and external residuals could be combined to achieve the best trade-off between fuel consumption and hydrocarbon emissions.

The effects of natural gas composition on conventional dual-fuel and reactivity-controlled compression ignition combustion in a heavy-duty diesel engine

The use of natural gas (NG) in dual-fuel heavy-duty engines has the potential to reduce pollutant and greenhouse gas (GHG) emissions from the transport sector when compared to the conventional diesel engines. However, NG composition and methane slip are of interest because both can adversely affect the benefits of NG as an alternative fuel, especially when considering GHG emissions. Therefore, this study experimentally investigated the effects of NG fuel properties on the performance and emissions of both conventional dual-fuel and reactivity-controlled compression ignition (RCCI) engine operations. Three different gas mixtures were selected to simulate typical NG compositions available in the world market, with methane numbers (MN) of 80.9, 87.6 and 94.1. These fuels were tested in a single-cylinder compression ignition engine operating at 0.6, 1.2 and 1.8 MPa net indicated mean effective pressure (IMEP). A high-pressure common rail system allowed for the use of various diesel injection strategies while a variable valve actuation system enabled the effective compression ratio to be adjusted via late intake valve closing (LIVC). The RCCI combustion was found to be more sensitive to changes in MN than the conventional NG-diesel dual-fuel operation. The gas mixture with the lowest MN reduced both total unburned hydrocarbons emissions and methane slip at the expense of higher nitrogen oxides (NOx) emissions. The effects of MN on the net indicated efficiency were more significant at 0.6 MPa IMEP, yielding differences of up to 4.9% between the RCCI operations with the lowest and highest MN fuels. Overall, this work revealed that the combination of the RCCI combustion and LIVC can achieve up to 80% lower methane slip and NOx emissions and relatively higher net indicated efficiency than the conventional dual-fuel regime, independent of the NG composition.

Performance and power consumption optimization of a hydraulic variable valve actuation system

A Hydraulic Variable Valve Actuation (HVVA) system is studied in this work, it can continuously adjust engine valve timing and lift at any engine speeds by using a hydraulic actuation system. A detailed co-simulation model is built to reveal relationship between hydraulic pressure, engine valve lift and power consumption, it has taken flow rate, fluid property and pressure drop into consideration. Precision and accuracy of the simulation model are verified by a set of bench test. Coefficient of variation (COV) of engine lift shows that the experiment is repeatable and system robustness is verified through simulation. A modified simulated annealing optimization is conducted to search optimum operation parameters to reduce the HVVA system's power consumption and improve engine's volumetric efficiency (VE) as well as control engine valve seating speed. A pre-selecting criterion and a database retrieve process are added in the algorithm to improve the optimization's efficiency. Optimization shows that optimum pump speed and relief pressure vary from 440 rpm, 32 bar to 2200 rpm, 60 bar when engine speed increases from 500 to 3600 rpm. Corresponding system power consumption rises from 0.07 kW to 0.49 kW, valve lift has a relatively high time-area value (TAV) and an acceptable engine valve seating speed.

Design and Analysis of a Fully Variable Valve Actuation System

With the problem of environmental pollution and energy shortage becoming more and more serious, the fuel efficiency of automobile engines has attracted much attention, and variable valve technology is one of the important technologies to solve this problem. A novel fully variable valve actuation (FVVA) system based on a brushless direct current motor (BLDCM) is designed to achieve fully variable valve adjustment. The system uses a crank-moving guide rod mechanism to convert the rotary motion of the BLDCM into the linear motion of the valve. The fully variable valve system can realize real-time continuous adjustment of valve operating parameters through the motion control of BLDCM, including variable valve timing, variable valve opening duration, and variable lift. A BLDCM and a transmission mechanism for the FVVA system is designed in this paper. In order to better analyze the performance of the system, a dynamic model is established. Then, a three closed-loop control method is adopted to realize position control of the valve. Finally, a complete system model is established to verify the theory conclusions. The results show that the system can realize fully variable valve adjustment.

Exploring the high load potential of diesel–methanol dual-fuel operation with Miller cycle, exhaust gas recirculation, and intake air cooling on a heavy-duty diesel engine

Legislations concerning emissions from heavy-duty diesel engines are becoming increasingly stringent. This requires conventional diesel combustion to be compliant using costly and sophisticated aftertreatment systems. Preferably, diesel–methanol dual-fuel is one of the suitable alternative combustion modes as it can potentially reduce the formation of nitrogen oxide and soot emissions which characterised the diesel mixing-controlled combustion. This is primarily due to the high latent heat of vaporisation and oxygen content of the methanol fuel. At high engine loads, however, the potential of diesel–methanol dual-fuel operation is constrained by the excessive combustion pressure rise rate and peak in-cylinder pressure, which limits both the engine efficiency and the percentage of methanol that can be used. For the first time, experimental studies were conducted to explore advanced combustion control strategies such as Miller cycle, exhaust gas recirculation, and intake air cooling for improving upon high load diesel–methanol dual-fuel combustion. Experiments were carried out at 1200 r/min and 18 bar indicated mean effective pressure on a single-cylinder heavy-duty diesel engine, which equipped with a high pressure common rail diesel injection, a methanol port fuel injection, and a variable valve actuation system on the intake camshaft. Results showed that the methanol energy fraction of a conventional diesel–methanol dual-fuel operation with a baseline intake valve closing timing was limited to 28%. This was due to the high combustion temperature at a high load which advanced the ignition timing of the premixed charge, resulting in high levels of pressure rise rate. The application of lower effective compression ratio and intake air temperature ( Tint) effectively decreased the compression temperature, which successfully delayed the ignition timing of the premixed charge. This allowed for a more advanced diesel injection timing to achieve improvement in the thermal efficiency and potentially enabled a higher methanol substitution ratio. Although the introduction of exhaust gas recirculation demonstrated very slight impact on the ignition timing of the premixed charge, a higher net indicated efficiency was observed due to a relatively lower local combustion temperature which reduced heat transfer loss. Moreover, the optimised diesel–methanol dual-fuel operation allowed a higher methanol energy fraction of 40% to be used at an effective compression ratio of 14.3 and Tint of 305 K and achieved the highest net indicated efficiency of 47.4%, improving by 3.7% and 2.6%, respectively, when compared to the optimised conventional diesel combustion (45.7%) and conventional diesel–methanol dual-fuel (46.2%). This improvement was accompanied with a reduction of 37% in nitrogen oxide emissions and little impact on soot emissions in comparison with the conventional diesel combustion.

Analysis and optimization of a variable mode valve actuation system

Braking safety of heavy-duty engines has always been the focus of the research, and the fuel economy and after-treatment thermal management during low-load operation of heavy-duty engines have also received much attention in recent years. A variable mode valve actuation system which can realize switching between four-stroke driving, two-stroke compression release braking and cylinder deactivation modes on a traditional four-stroke engine was proposed in this article. Two-stroke compression release braking mode of the variable mode valve actuation system can greatly enhance the braking safety, while the overload of valve train was a great challenge, especially during the release event. The effects of different release opening timing on cylinder pressure and the braking performance were studied. The results indicated that a higher cylinder pressure does not always lead to higher braking power. When the release opening timing was advanced by 6 °CA, the braking power reduced by only 9 kW (2.65%) at 1900 r/min compared with the initial value, while the maximum cylinder pressure reduced by 11.4 bar (20.8%). Besides, the variable mode valve actuation system can realize alternate three-cylinder cylinder deactivation mode on a six-cylinder turbocharged engine, which can improve the brake-specific fuel consumption by 14.67% and increase the turbine outlet temperature by 63.6 °C and reduce the exhaust flow rate by 50.66% at lightly load idle. Meanwhile, when the engine load is less than 50% at the rated speed, the three-cylinder cylinder deactivation mode can improve the brake-specific fuel consumption, increase the turbine outlet temperature and reduce the exhaust flow rate. The increase of the turbine outlet temperature and the decrease of the exhaust flow rate are very beneficial to improve the efficiency of the after-treatment thermal management of heavy-duty engines.

Analysis on possibility of expanding low-load operation area for homogeneous charge compression ignition in CI engine with variable exhaust valve actuation

Various technologies are being studied for the advancement of diesel passenger cars and associated environmental regulations. Effective compression ignition combustion in diesel engines is highly dependent on the cylinder charging temperature, composition, and cylinder pressure during valve train operation. The application of variable valve control in diesel engines has several potential advantages. In this study, we applied the variable valve actuation system to a single-cylinder engine model using a GT-POWER simulation and analyzed the effects of the recompression and rebreathing valve profiles, and fuel-injection pressure on the combustion characteristics of a compression ignition engine. As a result, NOx emissions were reduced by more than 90 %, while those of indicated mean effective pressure were reduced by up to 35 %. The benefits of recompression strategies in terms of NOx emissions reduction were confirmed.

Development of a variable mode valve actuation system for a heavy-duty engine

A new variable mode valve actuation system for a heavy-duty engine was proposed and designed in this paper. The variable mode valve actuation system can significantly enhance braking safety and improve fuel economy and emission of heavy-duty engines through flexible switching among four-stroke driving mode, two-stroke compression-release braking mode, and cylinder deactivation mode on a conventional four-stroke engine. The switching was controlled by four-stroke driving modules and two-stroke braking modules, both of which have two operation states: effective state and failure state. For the control of the multi-cylinder engine, all cylinders can be divided into several groups, and all the four-stroke driving modules in the same group were controlled by one solenoid valve, as well as all the two-stroke braking modules were controlled by another solenoid valve. A hydraulic-mechanical multi-body dynamics model was established to investigate the switching response of the variable mode valve actuation system. The results indicated that when the engine operated at 2000 r/min, the switching of the four-stroke driving module and the two-stroke braking module required 30 °CA and 101 °CA at most, respectively. In addition, to avoid the conflict between the four-stroke driving valve lift and the two-stroke braking valve lift, the switching between the four-stroke driving mode and the two-stroke compression-release braking mode must have a reasonable sequence. The variable mode valve actuation system has an excellent switching response and it is convenient for the control of the multi-cylinder engine. Therefore, the variable mode valve actuation system has a good application prospect for heavy-duty engines.

Review of Advancement in Variable Valve Actuation of Internal Combustion Engines

The increasing concerns of air pollution and energy usage led to the electrification of the vehicle powertrain system in recent years. On the other hand, internal combustion engines were the dominant vehicle power source for more than a century, and they will continue to be used in most vehicles for decades to come; thus, it is necessary to employ advanced technologies to replace traditional mechanical systems with mechatronic systems to meet the ever-increasing demand of continuously improving engine efficiency with reduced emissions, where engine intake and the exhaust valve system represent key subsystems that affect the engine combustion efficiency and emissions. This paper reviews variable engine valve systems, including hydraulic and electrical variable valve timing systems, hydraulic multistep lift systems, continuously variable lift and timing valve systems, lost-motion systems, and electro-magnetic, electro-hydraulic, and electro-pneumatic variable valve actuation systems.

Research on two-stroke compression release braking performance of a variable mode valve actuation system

In order to enhance the braking safety and improve the fuel economy and emission of heavy-duty engines, a variable mode valve actuation system which can switch operation modes flexibly among four-stroke driving, two-stroke compression release braking, and cylinder deactivation modes on a four-stroke engine was developed in this article. The switching was controlled by the four-stroke driving module and the two-stroke braking module, both of which have two states: effective state and failure state. Besides, a full-cycle numerical model of a six-cylinder turbocharged engine was established for the performance analysis of two-stroke compression release braking mode. The orthogonal design method was introduced in the present study to obtain the optimum valve parameters which can result in high braking power and maintain the maximum cylinder pressure at a lower level at the same time. Then, the two-stroke compression release brake braking power with the optimum valve parameters was compared with four-stroke compression release braking power. Meanwhile, the two-stroke braking cam profile of the variable mode valve actuation system was designed according to the optimum valve parameters, and the two-stroke braking performance with the dynamic valve lift of the variable mode valve actuation system was validated by the numerical model including the hydraulic system. The results indicated that a higher engine speed leads to higher braking power at the same valve lift. Besides, two-stroke compression release brake braking power of the variable mode valve actuation system achieved 525.3 kW at 2600 r/min and 358.1 kW at 1900 r/min, 52.9% and 71.3% higher than four-stroke compression release braking power, respectively. Although the two-stroke compression release brake braking power with dynamic valve lift is slightly less than that with the optimum valve parameters, it is still much higher than that of the four-stroke compression release braking power. Therefore, it has a good application prospect for heavy-duty engines.

Electro-pneumatic variable valve actuation system for camless engine: Part I-development and characterization

The intake and exhaust valves lift, timing, and duration influence the performance, combustion, and emissions of an internal combustion engine. In this study, an electro-pneumatic variable valve actuation (VVA) system was developed for independent control of the valve motion. The Shadowgraph technique was used to characterize the valve motion, and a high-speed camera was used to capture the valve images. It was observed that by controlling the airflow rate into the pneumatic actuator, different valve lifts were achieved successfully. However, the valve velocity at the end of backward stroke was so high that valve hits the valve seat. Therefore, pneumatic damping was introduced towards the end of backward stroke and valve velocity was reduced when valve comes in contact with the valve seat. Multi-cycle analysis for valve lift and velocity profiles were performed to evaluate cycle-to-cycle variations of the developed actuation system. The results show that the system performs well for both part and full lift conditions with coefficient of variation below 1% and has an acceptable valve seating velocity control. The developed VVA system will be used in Part-II and the effect of un-throttled operation on fuel consumption improvement in a camless engine will be investigated.

Electro-pneumatic variable valve actuation system for camless engine: Part II-fuel consumption improvement through un-throttled operation

Pumping loss during the gas exchange process becomes severe at low load operation in the conventional cam operated spark-ignition (SI) engine. In this study, the throttle body and conventional cam operated valve actuation mechanism of a single cylinder SI engine were removed. A novel in-house developed electro-pneumatic variable valve actuation system (VVA), as discussed in Part-I, was integrated and modified the conventional engine into camless engine. Air flow rates were varied using a throttle valve in the conventional engine. Whereas, for camess engine, air flow rates were varied by low intake valve lift and early intake valve closing (EIVC). It was found that the developed electro-pneumatic camless engine can inhale the same amount of air as compared to the conventional engine. The un-throttled operation in camless engine reduced the pumping loss at low engine speed and low load conditions, which helps in reducing the brake specific fuel consumption (BSFC) as compared to the conventional engine.

Variable valve actuation–based combustion control strategies for efficiency improvement and emissions control in a heavy-duty diesel engine

High nitrogen oxide levels of the conventional diesel engine combustion often requires the introduction of exhaust gas recirculation at high engine loads. This can adversely affect the smoke emissions and fuel conversion efficiency associated with a reduction of the in-cylinder air-fuel ratio (lambda). In addition, low exhaust gas temperatures at low engine loads reduce the effectiveness of aftertreatment systems necessary to meet stringent emissions regulations. These are some of the main issues encountered by current heady-duty diesel engines. In this work, variable valve actuation–based advanced combustion control strategies have been researched as means of improving upon the engine exhaust temperature, emissions, and efficiency. Experimental analysis was carried out on a single-cylinder heady-duty diesel engine equipped with a high-pressure common-rail fuel injection system, a high-pressure loop cooled exhaust gas recirculation, and a variable valve actuation system. The variable valve actuation system enables a late intake valve closing and a second intake valve opening during the exhaust stroke. The results showed that Miller cycle was an effective technology for exhaust temperature management of low engine load operations, increasing the exhaust gas temperature by 40 °C and 75 °C when running engine at 2.2 and 6 bar net indicated mean effective pressure, respectively. However, Miller cycle adversely effected carbon monoxide and unburned hydrocarbon emissions at a light load of 2.2 bar indicated mean effective pressure. This could be overcome when combining Miller cycle with a second intake valve opening strategy due to the formation of a relatively hotter in-cylinder charge induced by the presence of internal exhaust gas recirculation. This strategy also led to a significant reduction in soot emissions by 82% when compared with the baseline engine operation. Alternatively, the use of external exhaust gas recirculation and post injection on a Miller cycle operation decreased high nitrogen oxide emissions by 67% at a part load of 6 bar indicated mean effective pressure. This contributed to a reduction of 2.2% in the total fluid consumption, which takes into account the urea consumption in aftertreatment system. At a high engine load of 17 bar indicated mean effective pressure, a highly boosted Miller cycle strategy with exhaust gas recirculation increased the fuel conversion efficiency by 1.5% while reducing the total fluid consumption by 5.4%. The overall results demonstrated that advanced variable valve actuation–based combustion control strategies can control the exhaust gas temperature and engine-out emissions at low engine loads as well as improve upon the fuel conversion efficiency and total fluid consumption at high engine loads, potentially reducing the engine operational costs.

Combustion chamber design for a high-performance natural gas engine: CFD modeling and experimental investigation

Abstract The present paper is focused on the development of a high-performance, monofuel, spark ignition engine running on natural gas, featuring a high volumetric compression ratio and a variable valve actuation system. More specifically, the cylinder head geometry effect has been analyzed and the compression ratio has been optimized by means of steady-state and transient simulation activity, as well as of an extensive experimental campaign. The compression ratio effect was mainly investigated by means of experimental tests but a few 3D simulations were also run in order to quantify its impact on the in-cylinder tumble and turbulence. The main novelty of the paper are, first, the adoption of very high engine compression ratio values, second, the combined optimization of the cylinder head design and compression ratio. The main results can be summarized as follows. The engine configuration with mask showed a decrease in the average discharge coefficient by 20–30% and an increase in the tumble ratio by around 200% at partial load. Moreover, the simulation of the engine cycle indicated that the presence of the piston modifies the tumble structure with respect to the steady-state simulation case. An increase in the tumble number and turbulence intensity by around 90% and 10%, respectively, are obtained for the case with mask at 2000 rpm and 4 bar. With reference to the combustion duration, on an average, the presence of the masking surface led to a reduction of the combustion duration (from 1% to 50% of mass fraction burned) between 2 and 6 degrees. As far as the engine compression ratio is concerned, the value of 13 was finally selected as the best compromise between combustion variability, engine performance at full load and fuel consumption at partial load.