Variable Valve Timing Strategies Research Articles

Co-optimization and prediction of high-efficiency combustion and zero-carbon emission at part load in the hydrogen direct injection engine based on VVT, split injection and ANN

Hydrogen fuel holds great promise for accelerating the energy sector's decarbonization efforts. However, hydrogen's unique properties pose challenges for hydrogen direct injection (HDI) engines, such as differences in airflow exchange capabilities for very low density and reduced combustion rates due to lean burn conditions. This study investigates the impact of combined variable valve timing (VVT) and split injection strategies on HDI engine combustion, efficiency, and emissions. Using Artificial Neural Network (ANN) models and experimental data, predictive models for Brake Thermal Efficiency (BTE) and Nitrogen Oxide (NOx) emissions were developed. Adjusting intake and exhaust valve timings improved BTE by up to 2.5 % and 1.8 %, respectively, while reducing NOx emissions by 48.9 % and 31.1 % under specific conditions. Optimizing split injection alongside VVT further increased BTE by 1.2 % and 0.9 %, but increased NOx emissions by 29.9 % and 26.5 %. The flexible application of VVT and split injection strategies aims to balance efficiency gains with emissions control. The ANN-based models demonstrated high accuracy (R2 > 0.974), proving reliable substitutes for real-engine testing in certain conditions. In conclusion, this research highlights the potential of VVT and split injection strategies to enhance HDI engine performance while mitigating environmental impact, supporting the transition to sustainable energy solutions.

Optimizing hydrogen spark-ignition engine performance and pollutants by combining VVT and EGR strategies through numerical simulation

Hydrogen combustion engines are considered one of the leading solutions for decarbonizing road transport, mainly due to the possibility of adapting current engines for hydrogen operation with minor changes. This research extensively analyzes the effect of combined EGR (exhaust gas recirculation) and VVT (variable valve timing) strategies on the performance and emissions of a commercial turbocharged SI engine fueled with hydrogen. To this end, a 1D model of the said engine, widely validated for gasoline operation, was adapted to simulate the engine's behavior with hydrogen. This adaptation involved hardware changes and the implementation of a predictive hydrogen combustion submodel, previously calibrated using experimental data from a single-cylinder engine of similar geometry. Firstly, 400 hydrogen engine simulations without EGR were conducted to optimize the VVT system for fuel efficiency over a wide operating range. A detailed explanation of the causality of varying valve overlap on pumping losses, in-cylinder gas composition, and combustion is provided from these simulations. Then, a series of EGR sweeps were simulated to study its impact on performance and NOx at various degrees of load; concluding that diluting with EGR, rather than air, leads to reduced NOx emissions in exchange for slightly increased fuel consumption.

Experimental study on the load control strategy of ammonia-hydrogen dual-fuel internal combustion engine for hybrid power system

The development of hybrid technology and the use of zero-carbon fuels are effective means to improve energy efficiency and reduce carbon emissions. In this study, the Miller cycle spark ignition engine was used, and four load control strategies of throttle, ammonia-hydrogen ratio, air–fuel ratio, and variable valve timing were used to conduct experimental research on the ammonia-hydrogen engine. The experimental results show that the throttle strategy provides the widest output range, and the BMEP is raised from a minimum of 1 bar to 7.4 bar. The ammonia-hydrogen mixing ratio strategy is suitable for cold start conditions, fully utilizing the good combustion characteristics of hydrogen, and at the same time reducing the amount of hydrogen used in the heat engine process as much as possible. The air–fuel ratio strategy provides the highest thermal efficiency with a maximum BTE approaching 40%. It satisfies the energy-saving demand under the single-point working condition of the engine in the series mode. The variable valve timing strategy can realize switching between BMEP between 3.5 bar and 6.5 bar, and keep BTE above 33%. The valve timing strategy can not only provide a wider load adjustment range but also maintain high thermal efficiency. Finally, combining the effects of the four control strategies and the typical operating modes of the hybrid system, this study suggests that the throttle strategy is suitable for the feed mode, the VVT strategy is suitable for the parallel mode, the ammonia-hydrogen mixture ratio strategy is suitable for the cold start condition, and the air–fuel ratio control is suitable for the series mode.

Evaluation of the variable valve timing strategy in a direct-injection hydrogen engine with the Miller cycle under lean conditions

The favorable physicochemical characteristics of hydrogen make it an excellent alternative fuel for IC engines. Compared with hydrogen port injection, hydrogen direct injection provides multiple degrees of freedom for injection strategies and mixture formation, which can effectively suppress abnormal combustion and enhance engine performance. Variable valve timing (VVT) and the Miller cycle, as advanced and effective means of improving engine performance, are less investigated based on a direct-injection (DI) hydrogen engine. Hence, to optimize the performance of a DI hydrogen engine, strategies of the Miller cycle and VVT are introduced. In this work, a 1.5 L direct-injection engine with a VVT system was employed to evaluate the effects of the Miller cycle, intake valve closing (IVC) timing, and exhaust valve opening (EVO) timing on the airflow exchange process, in-cylinder charge characteristics, heat release process, dynamics and emission characteristics. The engine speed was stabilized at 1400 rpm and the strategies of lean combustion and late injection were used. The main results are as follows. As the IVC timing is delayed, the ratio of pumping mean effective pressure to indicated mean effective pressure (PMEP/IMEP) first decreases and then slightly increases, and the engine tends to achieve a high level of brake thermal efficiency (BTE) when PMEP/IMEP is lower. The optimization of intake and exhaust VVT can shorten combustion duration and reduce cyclic variation by increasing volumetric efficiency and improving mixture distribution at ignition timing. Furthermore, the engine reaches 42.22% BTE and a high level of brake mean effective pressure by the cooperative control of IVC and EVO timing. NOx emissions can be controlled below 100 ppm by employing the synergistic effect of the Miller cycle and VVT. It is worth mentioning that exhaust VVT as a way to compensate for the performance of the DI hydrogen engine with the Miller cycle should not be ignored.

A novel combined throttle opening and variable valve timing strategy for combined cooling, heating, and power system flexibility

The flexibility of combined cooling, heating, and power systems limits renewable energy penetration, supply–demand matching, and primary energy saving. The combined throttle opening and variable valve timing strategy adjust air flow, fuel consumption, and combustion duration, benefiting the operation range. The 1-D engine coupled with SIturb combustion model and quasi-steady absorption refrigerator were constructed. Traditional throttle opening and combined strategy are compared under a wide load range. The results indicate that exhaust energy was inversely correlated with brake thermal efficiency. The variable valve timing strategy regulated the exhaust energy to approach cooling load when power matched. The system operation range extended from a line to an area. At 100%, 70%, and 40% load, the adjustable cooling capacity was extended by 2.5%, 6.9%, and 28.9%, respectively. This suggests that the combined strategy improves the supply–demand matching, primary energy saving rate, and carbon dioxide emission reduction compared to the traditional throttle opening strategy.

Experimental and modeling analysis on the optimization of combined VVT and EGR strategies in turbocharged direct-injection gasoline engines with VNT

The combination of a growing number of complex technologies in internal combustion engines (ICE) is commonplace, due to the need of complying with the tight pollutant regulations and achieving high efficiencies. Hence the work of calibration engineers is led by a constant increase in degrees of freedom in ICE design. In this research work, a wide analysis on the optimization of combined variable valve timing (VVT) and exhaust gases recirculation (EGR) strategies is developed, in order to reduce fuel consumption in a EURO 6 1.3l 4-stroke 4-cylinder, gasoline, turbocharged, direct-injection engine, also equipped with a variable nozzle turbine (VNT). For that purpose, a methodology which combines 1D engine simulations with limited experimental work was applied. First, the data from 25 experimental tests distributed into three steady engine operating conditions was used to calibrate a 1D model. Then, modeling parametric studies were performed to optimize VVT and EGR parameters. A total of 150 cases were simulated for each operating point, in which VVT settings and EGR rate were varied at iso-air mass flow and iso-intake manifold temperature. The optimization was based on finding the configuration of VVT and EGR systems which maximizes the indicated efficiency. All different cases modeled were also evaluated in terms of pumping and heat losses. Moreover, a deep assessment of instantaneous pressure traces and mass flows in intake and exhaust valves was given, to provide insights about the optimization procedure. Finally, the findings obtained by simulation were compared with the results from a design of experiments (DOE) composed of more than 300 tests, and the impact on engine fuel consumption was analyzed.

Development of a Variable Valve Actuation Control to Improve Diesel Oxidation Catalyst Efficiency and Emissions in a Light Duty Diesel Engine

Growing interest has arisen to adopt Variable Valve Timing (VVT) technology for automotive engines due to the need to fulfill the pollutant emission regulations. Several VVT strategies, such as the exhaust re-opening and the late exhaust closing, can be used to achieve an increment in the after-treatment upstream temperature by increasing the residual gas amount. In this study, a one-dimensional gas dynamics engine model has been used to simulate several VVT strategies and develop a control system to actuate over the valves timing in order to increase diesel oxidation catalyst efficiency and reduce the exhaust pollutant emissions. A transient operating conditions comparison, taking the Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC) as a reference, has been done by analyzing fuel economy, HC and CO pollutant emissions levels. The results conclude that the combination of an early exhaust and a late intake valve events leads to a 20% reduction in CO emissions with a fuel penalty of 6% over the low speed stage of the WLTC, during the warm-up of the oxidation catalyst. The same set-up is able to reduce HC emissions down to 16% and NOx emission by 13%.

Diesel engine optimization and exhaust thermal management by means of variable valve train strategies

Due to the need to achieve a fast warm-up of the after-treatment system in order to fulfill the pollutant emission regulations, a growing interest has arisen to adopt variable valve timing technology for automotive engines. Several variable valve timing strategies can be used to achieve an increment in the after-treatment upstream temperature by increasing the residual gas amount. In this study, a one-dimensional gas dynamics engine model has been used to carry out a simulation study comparing several exhaust variable valve actuation strategies. A steady-state analysis has been done in order to evaluate the potential of the different strategies at different operating points. Finally, the effect on the after-treatment warm-up, fuel economy and pollutant emission levels was evaluated over the worldwide harmonized light vehicles test cycle. As a conclusion, the combination of an advanced exhaust (early exhaust valve opening and early exhaust valve closing) and a delayed intake (late intake valve opening and late intake valve closing) presented the best trade-off between exhaust temperature increment and fuel consumption, which achieved a mean temperature increment during low-speed phase of the worldwide harmonized light vehicles test cycle of 27 °C with a fuel penalty of 6%. The exhaust valve re-opening technique offers a worse trade-off. However, the exhaust valve re-opening leads to lower nitrogen oxide (29% less) and carbon monoxide (11% less) pollutant emissions.

Evaluation of variable compression ratio (VCR) and variable valve timing (VVT) strategies in a heavy-duty diesel engine with reactivity controlled compression ignition (RCCI) combustion under a wide load range

Variable compression ratio (VCR) and variable valve timing (VVT) are two effective strategies to adjust the effective compression ratio, which is beneficial for controlling the combustion process of advanced combustion modes. In this study, systematic evaluation of the two strategies was conducted based on reactivity controlled compression ignition (RCCI) engine in terms of combustion process control, fuel efficiency, and emission characteristics. By coupling an updated KIVA-3V code with the genetic algorithm, the combustion of a heavy-duty RCCI engine with VCR and VVT strategies was respectively optimized, aiming to simultaneously realize high fuel efficiency and low emissions. The optimal VCR and VVT strategies were compared under a wide load range. The results indicate that, at low and mid loads, high effective compression ratio, large premix ratio, and early fuel injection can be utilized to realize Euro 6 nitrogen oxides (NOx) limit with ultra-low soot emissions and low fuel consumption for both VCR and VVT strategies. The increase of load from low to mid narrows the optimal range of exhaust gas recirculation (EGR) rate for VVT strategy whereas the range for VCR strategy is still wide. At high load, compared to VVT strategy, a further decreased effective compression ratio can be utilized for VCR strategy, which allows early fuel injection, leading to the improvements of fuel efficiency and soot emissions. This suggests that the VCR strategy is more practical for high-load operation of RCCI combustion and the commercialization the RCCI engine in the future compared to VVT strategy.

Valve timing optimisation of a spark ignition engine with skip cycle strategy

Skip cycle strategy (SCS) is a stroke volume modulation method leading to reduction in pumping loss through deactivation of engine valves under part-load conditions. Although SCS achieves a significant fuel economy, it increases regulated pollutant emissions such as nitrogen oxide and unburned hydrocarbon in comparison to normal 4-cycle engine operation. This paper investigated normal cycle strategy, skip cycle strategy as well as combination of skip cycle strategy and variable valve timing strategy for a spark-ignition engine using one-dimensional numerical model. The skip cycle engine was modelled at several steady-state operation points and then optimised at best ignition timing providing maximum brake torque at each simulation case. The numerical results obtained for both normal cycle and skip cycle have been validated against the experimental data. After completing the validation of numerical results with engine test bench data for both normal and skip cycle operations, optimisation of intake and exhaust valve timing profiles have been carried out regarding advancing or retarding camshaft relatively to the crankshaft position. In case of SCS and variable valve timing application together, NOx concentration was reduced by 35.1%, 39.4%, 26.8% and HC emission was reduced by 54.9%, 49.3% and 47.4% on average for brake mean effective pressure load levels of 1, 2 and 3 bar respectively at all among engine speed ranges between 1200 and 1800 rpm compared to stand alone SCS strategy. Furthermore, no remarkable additional brake specific fuel consumption was observed for SCS plus variable valve timing strategy compared to stand alone SCS.

Potential of reactivity controlled compression ignition (RCCI) combustion coupled with variable valve timing (VVT) strategy for meeting Euro 6 emission regulations and high fuel efficiency in a heavy-duty diesel engine

As an effective strategy to control the combustion of advanced combustion modes, the application of variable valve timing (VVT) in reactivity controlled compression ignition (RCCI) combustion was investigated in this study. By coupling KIVA-3V code with genetic algorithm, the combustion of a heavy-duty engine with RCCI combustion combined with VVT strategy was optimized under a wide load range. At each load, six operating parameters including premix ratio (PR), intake valve closing (IVC) timing, start of injection, exhaust gas recirculation rate, intake pressure, and intake temperature were optimized to realize low-emission and high-efficiency combustion. The optimization results indicate that, at low load, high PR coupled with either late IVC or base IVC can be utilized for the realization of high thermal efficiency. At mid load, the base IVC strategy is integrated with high PR, while the late IVC strategy is coupled with low PR. At high load, only the strategy with late IVC and low PR can be used. The strategy with higher PR and earlier IVC timing exhibits better engine performance on thermal efficiency and soot emissions, while the strategy with lower premix ratio and later IVC timing is superior in ringing intensity. By optimizing the RCCI combustion with the VVT strategy, the Euro 6 NOx limit can be met while maintaining ultra-low soot emissions at low and mid load. However, at least one aftertreatment device is required to further eliminate the NOx or soot emissions at high load. Under the whole load conditions, satisfactory fuel consumption can be obtained.

Next Generation Diesel Engine Potential of Highly Integrated Exhaust Gas Aftertreatment

Different driving scenarios produce different challenges in respect of reducing journey-specific pollutant emission, as shown in Figure 1 using the example of the temperature level in the exhaust gas aftertreatment system. The following requirements can be derived: Open image in new window Figure 1 Vehicle speed profiles and exhaust gas temperature curves in the SCRF for journey profiles under review (© IAV) NOx conversion at low temperatures in low-load cycles NOx engine-out emission control at high loads [2] large spread of space velocity in the SCR catalyst [3, 4] constantly high NOx conversion rate at rising temperatures in the SCR on filter (SCRF) [3, 4]. While controlling emissions from high-load cycles is more of a dimensioning matter, controlling them in the low- temperature range is always more complex [3, 4]. At extremely low average driving speeds (down to stop-and-go in congestion situations), exhaust gas aftertreatment temperature can fall below light-off. If this is immediately followed by rapid acceleration, the high levels of engine-out emissions are not treated adequately. To avoid such situations, the exhaust gas aftertreatment system must be kept at a constant temperature. This requires the application of additional exhaust gas temperature management measures like calibration-based measures, strategies for variable valve timing (VVT), hybridisation and exhaust gas aftertreatment (EAT) positioning: With regard to the CO2 advantages, which must be maintained compared to the gasoline engine, typical calibration-based measures in relevant heating modes (e.g. retarding the start of injection, throttling, post-injection) are detrimental to fuel consumption and therefore not ideal [3, 4]. Regarding VVT strategies discussion focuses in particular on secondary exhaust valve lift and cylinder shutoff as these strategies can be implemented more or less without increases in consumption. Moderate temperature advantages can be achieved and HC and CO emissions reduced during low-load operation [5]. Hybridisation can have an adverse effect on exhaust gas temperature as the average power output in the driving cycle is reduced by the higher efficiency achieved in the powertrain. Measures, such as avoiding trailing throttle and low torque levels as well as active load control, are capable of providing significant temperature and emission-related advantages. Depending on the hybrid powertrain's topology, the engine operating point could be decoupled completely from the driving situation [1]. Avoiding temperature losses as well as minimising the light-off time is a primary criterion in designing the powertrain. Particularly in hybridised concepts, this produces degrees of freedom in positioning the turbocharging (TC) and EAT components. Positioning EAT upstream of the TC provides the optimum in relation to temperature losses and light-off behaviour, but also with regard to the efficiency of any heating and operating strategy measures.

Efficiency improvement for an unthrottled SI engine at part load

Variable valve timing (VVT) and cylinder deactivation (CDA) are promising methods in reducing fuel consumption and emission at part load in SI engines. An SI engine which uses electromagnetic valvetrain (EMV) will eliminate flow restriction from the throttle valve and produce higher indicated mean efficiency pressure (IMEP) due to the disabling of some of the working cylinders at part load. Therefore, pumping loss can be significantly reduced at part-load conditions. In addition, duration and timing of valve events are variably controlled at different operating conditions. This contributes to the improvement of engine efficiency. In this study, a dynamic model of an unthrottled SI engine has been developed to simulate the engine cycle. The model uses an EMV system that allows valvetrain control and cylinder deactivation techniques to be carried out in simulation flexibly. The simulated results find the optimal valve timing for different engine speeds. The optimal timing of intake valve closing depends on engine speed linearly, while the intake valve opening insignificantly influences engine performance. Additionally, this study also shows that cylinder deactivation modes can be successfully applied in improving engine efficiency at different engine loads. Different cylinder deactivation strategies have been applied for the full range of engine loads. It is concluded that the two-cylinder deactivation mode (50% CDA) considerably improves fuel consumption at low engine load. Meanwhile, one-cylinder deactivation (25% CDA) is an optimal fuel economy mode at medium engine load. With proper uses of VVT and CDA strategies, the efficiency of an SI engine can be increased more than 30% at low engine load and 11.7 % at medium engine load.

INFLUENCE OF AUXILIARY EXHAUST VALVE WITH VARIABLE TIMING ON SPARK IGNITION ENGINE PERFORMANCE

New Variable valve timing strategy based on using auxiliary valve having variable timing (VVT) is used in this study. The valve is driven by a new variable valve timing mechanism constructed for this purpose. The auxiliary valve acts as an exhaust valve and the experiments and simulation model are carried out at different loads. The results show that engine performance is improved at full load and worsens at part loads. The study proves that using an auxiliary exhaust valve having variable timing is not recommended in engines applications.

INFLUENCE OF AUXILIARY INTAKE VALVE WITH VARIABLE TIMING ON SPARK IGNITION ENGINE PERFORMANCE

A new variable valve timing strategy based on using an auxiliary valve having a variable timing (VVT) is used in this study. The valve is driven by a new VVT mechanism achieving valve duration and opening angle variations. The auxiliary valve acts as intake valve. Experiments and simulation models are carried out at different loads. The results show improvements in brake thermal efficiency, fuel consumption, volumetric efficiency, residual gas fraction and engine emissions over the whole range of load. Swirl and tumble ratios are decreased.

A modelling study into the effects of variable valve timing on the gas exchange process and performance of a 4-valve DI homogeneous charge compression ignition (HCCI) engine

Homogeneous charge compression ignition (HCCI) combustion mode is a relatively new combustion technology that can be achieved by using specially designed cams with reduced lift and duration. The auto-ignition in HCCI engine can be facilitated by adjusting the timing of the exhaust-valve-closing and, to some extent, the timing of the intake-valve-opening so as to capture a proportion of the hot exhaust gases in the engine cylinder during the gas exchange process. The effects of variable valve timing strategy on the gas exchange process and performance of a 4-valve direct injection HCCI engine were computationally investigated using a 1D fluid-dynamic engine cycle simulation code. A non-typical intake valve strategy was examined; whereby the intake valves were assumed to be independently actuated with the same valve-lift profile but at different timings. Using such an intake valves strategy, the obtained results showed that the operating range of the exhaust-valve-timing within which the HCCI combustion can be facilitated and maintained becomes much wider than that of the typical intake-valve-timing case. Also it was found that the engine parameters such as load and volumetric efficiency are significantly modified with the use of the non-typical intake-valve-timing. Additionally, the results demonstrated the potential of the non-typical intake-valve strategy in achieving and maintaining the HCCI combustion at much lower loads within a wide range of valve timings. Minimizing the pumping work penalty, and consequently improving the fuel economy, was shown as an advantage of using the non-typical intake-valve-timing with the timing of the early intake valve coupled with a symmetric degree of exhaust-valve-closing timing.

An investigation and evaluation of variable-valve-timing and variable-valve-actuation strategies in a diesel homogeneous charge compression ignition engine using three-dimensional computational fluid dynamics

A three-dimensional computational fluid dynamics modelling was carried out to investigate effects of variable valve timing (VVT) and variable valve actuation (VVA) on gas exchange and fuel-air mixing processes in a diesel homogeneous charge compression ignition (HCCI) engine with early fuel injection. Four VVT or VVA strategies were conducted for this study: first, a negative valve overlap (NVO) strategy with fixed exhaust-valve-opening (EVO) and intake-valve-closing (IVC) timings but variable valve lifts, referred to as the NVO strategy; second, the NVO strategy with fixed valve profiles but variable EVO and IVC timings, referred to as the EVO strategy; third, the NVO strategy with fixed valve lifts and fixed EVO and IVC timings but variable exhaust-valve-closing (EVC) and intake-valve-opening timings, referred to as the EVC strategy; fourth, VVA with just variable valve lifts, referred to as the VMAX strategy. The results indicate that suitable NVO settings will enhance in-cylinder tumble and then increase turbulence intensity before compression end, although the increased NVO has a negative contribution to swirl ratio. It was found that reducing valve lifts alone is not an efficient way to retain the residual gas, but the function of reduced valve lifts will become significantly obvious by combining it with increasing NVO. For the effect of NVO on in-cylinder temperature, longer NVO not only will increase in-cylinder temperature because of the higher residual gas rate but also will improve the in-cylinder temperature homogeneity. On lowering the maximum valve lift or increasing the NVO, the unmixed region of the in-cylinder charge shrinks. The fuel-rich region expands because of the high intake velocity and enhanced turbulence intensity. This is beneficial to the forming of a global homogeneous charge. It has been noted from the current study that, as the droplet distribution may be influenced more by the in-cylinder air motion caused by NVO when the average droplet size is smaller, it is recommended that future studies explore the effects of VVT and VVA on diesel HCCI mixing and combustion with various advanced fuel injection strategies.

Review and analysis of variable valve timing strategies—eight ways to approach

In internal combustion engines, particularly for spark ignition (SI) engines, valve events and their timings have a major influence on the engine's overall efficiency and its exhaust emissions. Because the conventional SI engine has fixed timing and synchronization between the camshaft and crankshaft, a compromise results between engine efficiency, performance, and its maximum power. By using variable valve timing (VVT) technology it is possible to control the valve lift, phase, and valve timing at any point on the engine map, with the result of enhancing the overall engine performance. To get full benefits from VVT, various types of mechanisms have been proposed and designed. Some of these mechanisms are in production and have shown significant benefits in improving engine performance. During the last two decades, remarkable developments have been seen in the field of VVT. This paper reviews the literature in the technology of intake and exhaust philosophies of VVT and their effects on the pressure—volume (PV) cycle of the engine. A single-cylinder engine is simulated by the GT-Power software. The effects of different VVT philosophies from the simulations are analysed and compared to those of the literature reviewed.

Influence of variable valve timings on the gas exchange process in a controlled auto-ignition engine

The controlled auto-ignition (CAI) engine concept has the potential to be highly effcient and to produce low NOx and particulate matter emissions. However, the problem of controlling the combustion over the entire load/speed range limits its practical application. The CAI combustion is controlled by the chemical kinetics of the charge mixture, with no influence of the flame diffusion or turbulent propagation. Therefore, to achieve successful control of the CAI process, the composition, temperature and pressure of the charge mixture at the inlet valve closure (IC) point have to be controlled. The use of the variable valve timing strategy, which enables quick changes in the amount of trapped hot exchaust gases, shows the potential for control of CAI combustion. The aim of this paper is to analyse the influence of the variable valve timing strategy on the gas exchange process, the process between the first valve open event (EO) and the last valve closing event (IC), in a CAI engine fuelled with standard gasoline fuel (95RON). The gas exchange process affects the engine parameters and charge properties and therefore plays a crucial role in determining the control of the CAI process. Analysis is performed by experimental and modelling approaches. A single-cylinder research engine equipped with a fully variable valvetrain (FVVT) system was used for the experimental study. A combined code consisting of a detailed chemical kinetics code and one-dimensional fluid dynamics code was used for the modelling study. The results obtained indicate that the variable valve timing strategy has a strong influence on the gas exchange process, which in turn influences the engine parameters and the cylinder charge properties, and hence the control of the CAI process. The EC timing has the strongest effect, followed by the IO timing, while the EO and IC timings have minor effects.