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Today's CI engines are subject to strict regulations of pollutant emissions and ambitious fuel consumption targets. Therefore, the interaction between the engine and the exhaust aftertreatment system (ATS) has become increasingly important. Numerous studies have shown that a variable valve train (VVT) improves the interaction between engine and ATS. However, most of these studies either quantify the advantage on a specific engine or only present complex CFD models, such that the results are not easily transferable to different engines. Thus, engine manufacturers cannot directly use these results to assess the advantage of various VVT strategies for their engines. In this paper, we propose a cycle-discrete cylinder model based on first principles which allows to simulate various VVT strategies. In contrast to present methods based on CFD, the proposed cylinder model can be realized with the equations presented. Furthermore, the model is identified with measurement data of an engine without a VVT. A separate engine, which is retrofitted with a fully VVT, is used to validate the proposed modeling approach. Using the identified model in combination with a mean-value model of the air path, we are able to simulate the effects of early intake valve closing, early exhaust valve opening, and cylinder deactivation for a complete CI engine that has no VVT installed. The model is then used to highlight the advantage of a VVT for two scenarios at part-load operation. At cold start, where the temperature of the ATS must be increased quickly, variable valve timing achieves higher enthalpy flows to the ATS while also lowering engine-out NOx emissions when compared to a standard engine strategy. If the ATS is at the operating temperature, cylinder deactivation achieves significantly higher enthalpy flows which prevents the ATS from cooling down. In addition, cylinder deactivation also lowers fuel consumption and engine-out NOx emissions. [ABSTRACT FROM AUTHOR]

The exhaust after-treatment (EAT) threshold temperature is a significant concern for highway vehicles to meet the strict emission norms. Particularly at cold engine start and low loads, EAT needs to be improved above 250 °C to reduce the tailpipe emission rates. Conventional strategies such as electrical heating, exhaust throttling, or late fuel injection mostly need a high fuel penalty for fast EAT warmup. The objective of this work is to demonstrate using a numerical model that a combination of the Miller cycle and delayed exhaust valve opening (DEVO) can improve the tradeoff between EAT warmup and fuel consumption penalty. A relatively low-load working condition (1200 RPM speed and 2.5 bar BMEP) is maintained in the diesel engine model. The Miller cycle via retarded intake valve closure (RIVC) is noticeably effective in increasing exhaust temperature (as high as 55 °C). However, it also dramatically reduces the exhaust flow rate (over 30%) and, thus, is ineffective for rapid EAT warmup. DEVO has the potential to enhance EAT warmup via increased exhaust temperature and increased exhaust flow rate. However, it considerably decreases the brake thermal efficiency (BTE)—by up to 5%—due to high pumping loss in the system. The RIVC + DEVO combined technique can elevate the exhaust temperature above 250 °C with improved fuel consumption—up to 10%—compared to DEVO alone as it requires a relatively lower rise in pumping loss. The combined method is also superior to RIVC alone. Unlike RIVC alone, the RIVC + DEVO combined mode does not need the extreme use of RIVC to increase engine-out temperature above 250 °C and, thus, provides relatively higher heat transfer rates (up to 103%) to the EAT system through a higher exhaust flow rate. The RIVC + DEVO combined method can be technically more difficult to implement compared to other methods. However, it has the potential to maintain accelerated EAT warmup with improved BTE and, thus, can keep emission rates at low levels during cold start and low loads. [ABSTRACT FROM AUTHOR]

A novel variable enhanced late intake valve closing (LIVC) Miller cycle with asynchronous valve opening was proposed. Relevant tests were carried out in a supercharged spark ignition (SI) engine with high compression ratio, which mainly included the effects of variable valve timing on performance and combustion characteristics, as well as the comparison with the baseline engine. The purpose of this study was to explore the effect of different intake and exhaust opening timing on the performance and combustion characteristics of the enhanced LIVC Miller cycle with asynchronous valve opening, and further explore the energy saving potential of this Miller cycle. The results showed that the application of variable enhanced Miller cycle effectively improved the anti-knock ability and pumping loss of the engine with high compression ratio. On the one hand, the optimization of pumping loss substantially improved the fuel economy under small load conditions. On the other hand, better combustion performance and air-fuel ratio could be achieved at medium and high loads. Meanwhile, the exhaust valve should be opened as earlier as possible to achieve the best fuel economy. Correspondingly, under optimal valve timing, compared with the baseline engine, the asynchronous intake valve opening variable enhanced Miller cycle engine with high compression ratio had a fuel economy optimization of more than 3.5 % under all loads, and the maximum fuel economy optimization was 12.74 % under the condition of 11 bar. • A novel variable enhanced LIVC Miller cycle with asynchronous valve opening was proposed. • Application of variable enhanced Miller cycle combined with high compression ratio. • Significant pumping loss optimization under low load conditions. • A maximum fuel economy optimization of 12.74 % is achieved. [ABSTRACT FROM AUTHOR]

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. • Combined IVC and EVC timing control significantly improves BTE and NOx emissions. • Combined regulation of SEOI and SIF further increased BTE but worsened NOx emissions. • VVT + split injection strategies should be considered to balance efficiency and cleanliness. • ANN-based high-precision BTE and NOx emission prediction models were developed. [ABSTRACT FROM AUTHOR]

Nowadays, vehicle industries are trying to introduce actively controllable variable valve trains to achieve maximumly efficient internal combustion engines. The electromagnetic valve train (EMV) is one of the promising valve actuators. A traditional electromagnet valve needs to be continuously supplied with current and consumes more energy during valve opening and closing, and the permanent magnet-assisted valves have a demagnetization issue. Thus, this study presents a hybrid permanent magnet electromagnetic valve (PMEMV), which needs a power supply only for a short interval of time during valve opening or closing; eventually, this PMEMV consumes much less energy than conventional EMVs. This paper proposed an improved control approach for this hybrid PMEMV to achieve variable valve actuation. Magnetic stimulation was performed on the proposed valve train to analyze the direction of the magnetic circuit during the valve actuation. An improved magnetic circuit control method was introduced to achieve the release and attraction of the armature. This innovative magnetic circuit control can make the armature effectively attract at each apex, so that the PMEMV can be effectively and completely actuated. The prototype of the valve train and the experimental platform were developed to test and validate the real-time performance of the composite EM valve. Peripheral sensor components were used to measure the valve displacement. The experimental results proved that the concept of the innovative magnetic-circuit drive and control can enable the successful operation of the hybrid compound EM valve. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) fluid devices are widely used in active automotive control applications. However, MR fluid-based valve actuators are not in the limelight. This paper proposes a new flexible valve train with an MR fluid control system; the valve train can enhance the performance of internal combustion engines. A major component of this valve train is the magnetic plate block filled with MR fluid and surrounded by a magnetic coil. This plate block controls the magnetic field in this MR fluid and eventually facilitates flexible valve lifts and valve opening timings. This study overviewed the conceptual design, two-way coupled multi-physics numerical simulations, manufactured an MR valve prototype, and conducted experimental tests on a test bench to understand the real-time performance of the MR valve train. First, computer simulations were performed using a coupled magnetic and thermal multiphysics model to consider the Joule-heating effect of the magnetic coil in the MR magnetic plate block. The simulation results indicated that although the temperature of the MR fluid increased noticeably, it did not exceed the prescribed operating limits. The dimensions of the MR magnetic plate block were optimized. After computer simulations and optimization, a prototype of the proposed MR valve was fabricated and tested to understand its performance in real time. The experimental test results indicated the reliability of the proposed MR valve train in practical scenarios. [ABSTRACT FROM AUTHOR]

Recently, many studies have been conducted on the conversion of conventional fossil fuels to alternative fuels. Natural gas is one of the best alternative fuels because it is a low-carbon fuel. In natural gas engines, port fuel injection is generally adopted rather than direct injection because of the compatibility of the injection system in a positive ignition engine. However, methane, of which the global warming potential is 28 times than that of carbon dioxide, is highly likely to emit during the valve overlap in port fuel injection engines. The methane slip phenomenon could be reduced by changing the intake and exhaust valve timing. However, few studies have discussed engine performance and emission characteristics through valve timing changes in natural gas engines. Therefore, in this study, experiments were conducted under the valve timing variations with/without boosting in a natural gas engine. Through experiments, it was possible to investigate the trend of engine performance and methane emission according to the change in the intake and exhaust valve timing. As a result, under the boosted condition, the intake valve timing could only be advanced up to 45 CAD bTDC and the exhaust valve timing could only be retarded by 27.4 CAD bBDC. This is because the methane slip phenomenon increased and it resulted in a decrease of engine torque when the intake valve timing was excessively advanced or the exhaust valve timing was inordinately retarded under the boosted condition. In addition, considering a level of methane emission equivalent to EURO-6, the valve timings were optimized for each engine speed point of 1000–2500 rpm under boosted high load conditions. It was found that the trend of intake valve timing of the natural gas engine was unlike that of the conventional gasoline engine under the low engine speed of less than 2500 rpm.

The exhaust after-treatment (EAT) threshold temperature is a significant concern for highway vehicles to meet the strict emission norms. Particularly at cold engine start and low loads, EAT needs to be improved above 250 °C to reduce the tailpipe emission rates. Conventional strategies such as electrical heating, exhaust throttling, or late fuel injection mostly need a high fuel penalty for fast EAT warmup. The objective of this work is to demonstrate using a numerical model that a combination of the Miller cycle and delayed exhaust valve opening (DEVO) can improve the tradeoff between EAT warmup and fuel consumption penalty. A relatively low-load working condition (1200 RPM speed and 2.5 bar BMEP) is maintained in the diesel engine model. The Miller cycle via retarded intake valve closure (RIVC) is noticeably effective in increasing exhaust temperature (as high as 55 °C). However, it also dramatically reduces the exhaust flow rate (over 30%) and, thus, is ineffective for rapid EAT warmup. DEVO has the potential to enhance EAT warmup via increased exhaust temperature and increased exhaust flow rate. However, it considerably decreases the brake thermal efficiency (BTE)—by up to 5%—due to high pumping loss in the system. The RIVC + DEVO combined technique can elevate the exhaust temperature above 250 °C with improved fuel consumption—up to 10%—compared to DEVO alone as it requires a relatively lower rise in pumping loss. The combined method is also superior to RIVC alone. Unlike RIVC alone, the RIVC + DEVO combined mode does not need the extreme use of RIVC to increase engine-out temperature above 250 °C and, thus, provides relatively higher heat transfer rates (up to 103%) to the EAT system through a higher exhaust flow rate. The RIVC + DEVO combined method can be technically more difficult to implement compared to other methods. However, it has the potential to maintain accelerated EAT warmup with improved BTE and, thus, can keep emission rates at low levels during cold start and low loads.

The pursuit of increasing the efficiency of internal combustion engines is an ongoing engineering task that requires numerous research efforts. New concepts of injection or combustion systems require preliminary investigation work using research engines. These engines, usually single-cylinder, make it possible to isolate a single variable in a complex combustion mixture preparation process, thus enabling analysis of the changes being made. However, these engines are relatively expensive and their designs are offered by a limited number of manufacturers. The authors of this paper have successfully undertaken the engineering task of modifying an existing research engine cylinder head in such a way as to implement an electronically controlled variable valve timing system of the intake system. The process of reverse engineering, together with design assumptions that finally contributed to the construction of the assumed solution has been described in this paper. [ABSTRACT FROM AUTHOR]

Nowadays, vehicle industries are trying to introduce actively controllable variable valve trains to achieve maximumly efficient internal combustion engines. The electromagnetic valve train (EMV) is one of the promising valve actuators. A traditional electromagnet valve needs to be continuously supplied with current and consumes more energy during valve opening and closing, and the permanent magnet-assisted valves have a demagnetization issue. Thus, this study presents a hybrid permanent magnet electromagnetic valve (PMEMV), which needs a power supply only for a short interval of time during valve opening or closing; eventually, this PMEMV consumes much less energy than conventional EMVs. This paper proposed an improved control approach for this hybrid PMEMV to achieve variable valve actuation. Magnetic stimulation was performed on the proposed valve train to analyze the direction of the magnetic circuit during the valve actuation. An improved magnetic circuit control method was introduced to achieve the release and attraction of the armature. This innovative magnetic circuit control can make the armature effectively attract at each apex, so that the PMEMV can be effectively and completely actuated. The prototype of the valve train and the experimental platform were developed to test and validate the real-time performance of the composite EM valve. Peripheral sensor components were used to measure the valve displacement. The experimental results proved that the concept of the innovative magnetic-circuit drive and control can enable the successful operation of the hybrid compound EM valve.

Magnetorheological (MR) fluid devices are widely used in active automotive control applications. However, MR fluid-based valve actuators are not in the limelight. This paper proposes a new flexible valve train with an MR fluid control system; the valve train can enhance the performance of internal combustion engines. A major component of this valve train is the magnetic plate block filled with MR fluid and surrounded by a magnetic coil. This plate block controls the magnetic field in this MR fluid and eventually facilitates flexible valve lifts and valve opening timings. This study overviewed the conceptual design, two-way coupled multi-physics numerical simulations, manufactured an MR valve prototype, and conducted experimental tests on a test bench to understand the real-time performance of the MR valve train. First, computer simulations were performed using a coupled magnetic and thermal multiphysics model to consider the Joule-heating effect of the magnetic coil in the MR magnetic plate block. The simulation results indicated that although the temperature of the MR fluid increased noticeably, it did not exceed the prescribed operating limits. The dimensions of the MR magnetic plate block were optimized. After computer simulations and optimization, a prototype of the proposed MR valve was fabricated and tested to understand its performance in real time. The experimental test results indicated the reliability of the proposed MR valve train in practical scenarios.

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. [ABSTRACT FROM AUTHOR]

A validated spark ignition engine combustion model was used to investigate the operational feasibility of subjecting a 5.734 l, V8 engine to the Honda variable (valve) timing and electronic lift control (VTEC) management strategy. The numerical results were found to be in good agreement with measured data during the compression and expansion strokes. However, the results of the numerical model overestimated the measured data by approximately 10%–15% during the combustion phase. The reason for this discrepancy could be due to the fact that the turbulence levels within the combustion chamber during the experiment was not specified. Therefore, we accounted for turbulence in the simulation with a flame speed multiplying factor, f t = 7.0. The investigations cover operations at low, mid-range and full power periods; for fuel-air equivalence ratios, ϕ of 0.67 , 1.10 a n d 1.18. The results of the study show that operational viability of a 5.734 l, V8 engine when subjected to the VTEC engine management scheme was achievable, provided high levels of turbulence were maintained, especially for extra lean mixtures, that is, for fuel-air equivalence ratio, ϕ = 0.67. This work shows that the values of the flame speed factor, f t have to be carefully selected in order to achieve complete combustion. [ABSTRACT FROM AUTHOR]

• Passive pre-chamber internal flow characteristics, combustion, and energy conversion analysis. • Analysis of combustion and emission for TJI hydrogen engines at different conditions. • The effect of variable valve timing and spark timing on TJI hydrogen engines. • The spark timing has a relatively minor effect on the power output of the TJI hydrogen engine. • Variable valve timing can improve the power and reduce cycle-to-cycle variation. To reduce carbon emissions, the application of hydrogen as a zero-carbon fuel in the field of internal combustion engines (ICEs) has become a hot topic in recent years. Meanwhile, the application of ignition methods such as turbulent jet ignition (TJI) in engines has been gradually attracting the interest of numerous scholars. However, there is a lack of research on the performance of the hydrogen-fueled engine with passive pre-chamber (PPC). This paper aims to explore the combustion and emission performance of TJI hydrogen engines under different load conditions through experimental and numerical methods. This study is based on a Miller cycle engine equipped with the PPC, where hydrogen is injected directly into the cylinder. The operational characteristics of internal flow field characteristics, combustion, and energy conversion in the PPC are revealed by numerical. The engine operates at a speed of 1600 rpm and an excess air ratio (λ) of 1.8. The results show that at a manifold absolute pressure (MAP) of 40 kPa, the brake mean effective pressure (BMEP) is 0.95 bar, and the brake thermal efficiency (BTE) is 17.26 %, with the coefficient of variation (COV) of the indicated mean effective pressure (COV IMEP) of 3.3 %. Although BMEP can be increased to 5.3 bar, BTE is 40.3 %, and COV IMEP can be reduced to 1.1 % under WOT, emissions have significantly increased. Additionally, the study explores the effect of variable valve timing (VVT) and spark timing (ST) on the performance of the hydrogen engine with PPC under partial load conditions. The results indicate that the ST has an insignificant influence on the power performance of TJI hydrogen engines, but delaying the ST could reduce nitrogen oxide (NOx) emissions. By appropriately delaying the timing of the intake valve opening (IVO), not only the power performance of TJI hydrogen engines could be improved, but also the COV IMEP could be reduced. [ABSTRACT FROM AUTHOR]

• Modelling and experimental results of reciprocating expander were presented. • Variable valve timing was employed to control the expansion ratio of the expander. • The expander provide 2.5 kW power output and 70% isentropic efficiency. • Dynamic model predicts torque and pressure traces with reasonable accuracy. • Model predicts power and isentropic efficiency within ±10% and ±30% accuracy. This paper presents a reciprocating expander concept for organic Rankine cycle applications using a novel rotating variable timing admission valve system, enabling the adjustment of the expansion ratio in real time while the expander is running. An organic Rankine cycle experimental test rig with n-pentane as the working fluid and a single-cylinder reciprocating piston expander was developed. Experiments were conducted for evaporation temperatures ranging from 125 °C to 150 °C and condensation temperatures ranging from 20 °C to 40 °C. The performance of the reciprocating piston expander was investigated in terms of the torque of the expander, pressure inside the cylinder, isentropic efficiency of the expander, and net power produced by the expander. Based on the experimental data, a dynamic model of the system was formulated in the object-oriented language, Modelica. The model was validated using the experimental results and then used to predict the performance of the expander. Special attention was paid to the robust modelling of the valve actuation to avoid computational inefficiencies caused by singularities of state variables or their derivatives. The results indicate that the expander produces up to 2.5 kW of electricity from a low-temperature heat source while operating at pressure ratios ranging from 10 to 16.5 with an isentropic efficiency of approximately 70%. The relative differences between the model and the measurements of the isentropic efficiency and power output of the expander per revolution were ±10% and ±30%, respectively. [ABSTRACT FROM AUTHOR]

In this study, a prototype four-stroke spark ignition engine with four cylinders (two valves per cylinder), with and without turbocharger, as well as variable valve timing system to adjustment of variable valve duration has been investigated. This study covers the effects of intake valve opening (IVO), Intake valve closing (IVC), exhaust valve opening (EVO) and exhaust valve closing (EVC) angles on engine performances and fuel economy. The calculations of engine performance were carried out using the 1-Dimensional simulation with AVL BOOST software. The effects of different valve timing strategies and a combination of them from simulations were analyzed and compared with the reference fixed valve timing cases. It was shown that substantial improvements in fuel consumption and performance can be achieved. The improvements of Indicated Specific Fuel Consumption (ISFC) are remarkable in turbocharged models. Furthermore, we can see the noticeable improvements in torque and power in the naturally aspirated engine. [ABSTRACT FROM AUTHOR]

In this paper, various modern power engines developed by the American, Japanese, and European automobile industries will be compared. Specific data, including the efficiency, emission rate of nitrogen oxides (NOx), fuel consumption, and electronic vehicle technology, will be developed. Since the first invention of the automobile engine in the late 19th century, companies came up with unique innovations, including its structure, control systems, and additional mechanical installations to improve efficiency and reduce emissions. Numerous companies, including Ford, Toyota, and Mercedes-Benz, compete in the automobile industry to improve their engine’s efficiency and emission rates to create a clean environment. In addition, each country has its regulations on emission rates and automobile structure. Therefore, to meet these regulations, the structure and the system of the engines vary between companies in different countries. A variety of variable valve timing (VVT) systems, which is a mechanical part installed in the engine, are being developed by several companies. The VVT controls the opening and closing of the air inlet valve and the exhaust valve, which improves the reduction of fuel consumption and thermal efficiency. Furthermore, changing the engine structure is also another method that automobile companies are developing. Changing the engine’s shape can improve the vehicle’s performance (e.g., the engine vibration while running, the power output, and the smoothness of driving). Due to the emissions caused by petrol and diesel engines, the electrified vehicles have been developing to achieve a cleaner environment. This includes battery electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and fuel cell electric vehicles. By comparing these features in the engine, it is possible to understand what the companies in the US, Japan, and the European countries are working on to improve their engines and provide a clean environment.

Recent announcements regarding the phase out of internal combustion engines indicate the need to make major changes in the automotive industry. Bearing in mind this innovation trend, the article proposes a new approach to the engine design. The aim of this paper is to shed a new light on the forgotten concept of axial engines with wobble plate mechanism. One of their most important advantages is the ease of use of the opposed piston layout, which has recently received much attention. Based on several years of research, the features determining the increase in mechanical efficiency, lower heat losses and the best scavenging efficiency were indicated. Thanks to the applied Variable Compression Ratio (VCR), Variable Angle Shift (VAS) and Variable Port Area (VPA) systems, the engine can operate on various fuels in each of the Spark Ignition (SI), Compression Ignition (CI) and Homogeneous Charge Compression Ignition (HCCI)/Controlled Auto Ignition (CAI) modes. In order to quantify the potential of the proposed design, an initial research of the newest PAMAR 4 engine was presented to calculate the torque curve at low rotational speeds. The achieved torque of 500 Nm at 500 rpm is 65% greater than the maximum torque of the OM 651 engine of the same 1.8 L capacity. The findings lead to the conclusion that axial engines are wrongfully overlooked and can significantly improve research on new trends in pollutant elimination.

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%.

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, NO x 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. [ABSTRACT FROM AUTHOR]

The influences of VVT on engine power performance were well summarized in previous studies from various aspects. However, most of the previous investigations were qualitative analysis and focused on the total effects of VVT without decoupling the influence factors. The primary cause is due to lack of an effective mathematic model to predict the IMEP of VVT engine. In this study, an approach to detect the VVT signals of engine was proposed, and the influence factors of power performance of VVT engines were quantitatively studied. The fundamental relationships among IMEP and its influencing parameters, i.e., intake density, intake VVT, RGF and thermal efficiency, were decoupled and the governing equation of IMEP was derived with the influences of VVT considered, the calculated results through which are in good agreement with tested data. Results indicate that, IMEP is directly proportional to effective cylinder volume at IVC timing and inversely proportional to RGF. The change rate of RGF influence coefficient is almost three times as that of RGF, and the combined effects of these parameters on IMEP equals the product of the coefficients of four influence factors. All these extended engine thermodynamics and provided theory basis for improving VVT engine's power performance. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of a four stroke spark ignition engine, using Diesel- RKl software. The models created in this digital tool are Multi-Zone type, and they rely on other submodels, defined by the authors, that are inserted in the main model. These submodels are the friction, the fuel, the gas exchange, the heat exchanges and the combustion, with an emphasis in the last one, which is offundamental importance for the achievement of the results. With the model created, adjusted to the experimental data, a second phase of obtaining result has began; changes in the intake and exhaust valves opening have been proposed in order to find conditions capable to reduce specific fuel consumption. At the end of the work, it has been observed that it would be possible to obtain a reduction o f the specific fuel consumption of up to 13%, to certain conditions of operation, however, the applicability of these results cannot be guaranteed due to some environmental law requests. [ABSTRACT FROM AUTHOR]

Exhaust gases remaining inside the engine cylinder after the exhaust stroke premix with fresh air-fuel combustible mixture and affect combustion process in the engine cylinder. Due to significantly higher temperature of these exhaust residuals (ExR) compared to the external exhaust gases recirculation (EGR), their impact on the in-cylinder combustion process is also different from impact of EGR. To control amounts of ExR independent of engine working parameters, the variable valve timing was introduced. It is known that variable valve timing affects not only volumetric efficiency and performance of the internal combustion reciprocating engine but also influences the amount of exhaust residuals remaining in the engine cylinder. These exhaust residuals impact combustion rates, combustion stability, knock and also play crucial role on exhaust toxic emissions. In this manuscript, the effect of variable valve overlap was studied on A. exhaust toxic emission (NOx, CO and THC), and B. combustion phasing and engine performance on a spark ignited natural gas fueled engine. The investigation was carried out in a single cylinder research engine at constant load. The engine was equipped with high authority dual independent cam phasors for both intake and exhaust values, but for the purpose of this study, the exhaust valve timing was fixed and intake valve timing was changed to vary the amount of exhaust residuals remaining in the engine cylinder. The correlation between valve overlap and exhaust residuals were determined. It was observed that correlation in the positive overlap range between 55 and 85 deg was almost positive linear. Regarding toxic exhaust emission, increase in exhaust residuals from 9.6 to 12.3% (change by 28%) caused reduction in NOx by 67% and increase in both CO and THC by approximately 75%. Additionally, it did not significantly affect the engine’s specific fuel consumption. Summarizing, strong correlation between in-cylinder exhaust residuals and toxic emissions, and combustion phases exists in the methane fueled spark ignited engine equipped with VVT. [ABSTRACT FROM AUTHOR]

Cogging torque assisted motor drives (CTAMD) are a novel electromechanical valve actuation (EVA) technology for internal combustion engines that have a compact size and do not require conventional valve springs. Despite using an unoptimized position trajectory, the CTAMD was shown to produce the smallest ohmic loss at 6000 RPM when compared with other EVA systems found in literature. This paper presents a minimum-energy trajectory for a CTAMD and validates its improvements. First, an ohmic loss model for the CTAMD is formulated. Next, the optimized trajectory is generated through the use of the Nelder–Mead direct search algorithm. The optimized trajectory is then tested on a previously studied experimental CTAMD setup. Finally, the results of the experiments are analyzed to determine the performance improvements and practical advantages of the optimized trajectory. The optimized trajectory enables a further reduction of ohmic loss and reduces the number of MOSFETs required to drive the CTAMD by 75%. [ABSTRACT FROM AUTHOR]

The knock phenomenon is one of the major hindrances for enhancing the thermal efficiency in spark-ignited engines. Due to the stochastic behavior of knocking combustion, analytical cycle studies are required. However, there are many problems to be addressed with regard to the individual cycle analysis of in-cylinder pressure data. This study thus proposes novel, comprehensive and efficient methodologies for evaluating the knocking combustion in the internal combustion engine. The proposed methodologies include a filtering method for the in-cylinder pressure, the determination of the knock onset, and the calculation of the residual gas fraction. Consequently, a smart knock onset model with high accuracy could be developed using a supervised deep learning that was not available in the past. Moreover, an improved zero-dimensional (0D) estimation model for the residual gas fraction was developed to obtain better accuracy for closed system analysis. Finally, based on a cyclic analysis, a knock prediction model is suggested; the model uses 0D ignition delay correlation under various experimental conditions including aggressive cam phase shifting by a dual variable valve timing (VVT) system. Using the proposed analysis method, insight into stochastic knocking combustion can be obtained, and a faster combustion speed can lead to a higher knock intensity in a steady-state operation.

We propose a novel axis-symmetric modified hybrid permanent magnet (PM)/electromagnet (EM) magnetomotive force actuator for a variable valve timing camless engine. The design provides a large magnetic force with low energy consump-tion, low coil inductance, PM demagnetization isolation, and improved transient response. Simulation and experimental results confirm forces of about 200 N (in the presence of coil current) at the equilibrium position and 500 N (in the absence of coil current) at the armature seat. We compared our proposed design with a double solenoid valve actuator (DSVA). The finite element method (FEM) designs of the DSVA and our proposed valve actuator were validated by experiments performed on manufactured prototypes. [ABSTRACT FROM AUTHOR]

The apparently simple structure of a four-stroke internal combustion cylinder belies the complicated problem of optimizing valve operation in response to a change in crankshaft rotation speed. The objective of this study was to determine the cylinder pressure for valve event angles in order to determine the optimal strategy for the timing of valve events when independently-actuated valves are available. In this work, an artificial neural network is applied to create a prediction matrix to anticipate the best variable valve timing approach according to rotation speed. [ABSTRACT FROM AUTHOR]

Study on rotary valve system (RVS) for automotive engines has been carried out over many years. Recent researches have already successfully implemented the idea, but none of design can provide variable valve timing and flow area control simultaneously. Therefore, a RVS with variable valve control system is proposed in this paper. The system design and dynamic analysis of the proposed RVS are first presented. Moreover, the selection of the proportional, integral and derivative (PID) controller parameters for the valve control based on an emerging artificial intelligent technique, cuckoo search (CS), is also discussed. Experimental and simulation results show that the proposed tuning method is better than the traditional Ziegler and Nichols method, and the proposed variable rotary valve control system is feasible. [ABSTRACT FROM AUTHOR]

Estimation of the air charge and the volumetric efficiency is one of the most challenging tasks in the control of internal-combustion engines owing to the intrinsic complexity and the non-linearity of the gas flow phenomena. In particular, with emerging new technologies such as systems with variable valve timing and variable valve lift, the number of effective parameters increases greatly, making the estimation task more complicated. On the other hand, using a three-way catalyst converter needs strict control of the air-to-fuel ratio to around the stoichiometric ratio, and hence more accurate models are required for estimation of the air charge. Therefore, various models have been proposed in the literature for estimation of the volumetric efficiency and the air charge. However, they are either strictly based on physical first principles, making them impractical for conventional applications, or nearly fully empirical and need many experimental data for calibration. In this paper, using a novel approach, a new semiempirical model is proposed for estimation of the volumetric efficiency, which is calibrated with very few experimental data and can be used easily for real-time applications. In addition to the valve timings, the engine speed and the intake manifold pressure, the inlet valve lift is also considered as the model input. The generalizability of the model is proved by applying it to estimate the volumetric efficiency of six different engines. Furthermore, a systematic approach is taken to simplify the proposed model and to strengthen its prediction capability. The result is a simple, practical and generalizable model which can be used for various spark ignition engines, can be trained with very few data and can be utilized for estimating accurately the volumetric efficiency in real-time applications. [ABSTRACT FROM AUTHOR]

Volumetric efficiency and air charge estimation is one of the most demanding tasks in control of today's internal combustion engines. Specifically, using three-way catalytic converter involves strict control of the air/fuel ratio around the stoichiometric point and hence requires an accurate model for air charge estimation. However, high degrees of complexity and nonlinearity of the gas flow in the internal combustion engine make air charge estimation a challenging task. This is more obvious in engines with variable valve timing systems in which gas flow is more complex and depends on more functional variables. This results in models that are either quite empirical (such as look-up tables), not having interpretability and extrapolation capability, or physically based models which are not appropriate for onboard applications. Solving these problems, a novel semi-empirical model was proposed in this work which only needed engine speed, load, and valves timings for volumetric efficiency prediction. The accuracy and generalizability of the model is shown by its test on numerical and experimental data from three distinct engines. Normalized test errors are 0.0316, 0.0152 and 0.24 for the three engines, respectively. Also the performance and complexity of the model were compared with neural networks as typical black box models. While the complexity of the model is less than half of the complexity of neural networks, and its computational cost is approximately 0.12 of that of neural networks and its prediction capability in the considered case studies is usually more. These results show the superiority of the proposed model over conventional black box models such as neural networks in terms of accuracy, generalizability and computational cost. [ABSTRACT FROM AUTHOR]