Research on Homogeneous Charge Compression Ignition Combustion of Intake Port Exhaust Gas Recirculation Based on Cam Drive Hydraulic Variable Valve Actuation Mechanism

The thermal efficiency of an efficient gasoline engine is only about 40% and it will produce a large number of harmful products. Curbing harmful emissions and enhancing thermal efficiency have always been the goals pursued and emission regulations are also being tightened gradually. As one of the main consumers of fossil fuels, automobile engines must further reduce fuel consumption and emissions to comply with the concept of low-carbon development, which will also help them compete with electric vehicles. Homogeneous charge compression ignition (HCCI) combustion combined with variable valve actuation (VVA) technology is one of the important ways to improve engine emissions and economy. HCCI combustion based on VVA can only be realized at small and medium loads. The actual application on the entire vehicle needs to be combined with spark ignition (SI) combustion to achieve full working condition coverage. Therefore, HCCI combustion needs fast valve response characteristics; however, the valve lift and timing of the existing VVA mechanisms are mostly controlled separately, resulting in poor valve response. In order to solve this problem, the cam driven hydraulic variable valve actuation (CDH-VVA) mechanism was designed. The valve lift and timing can be adjusted at the same time and the switching of valve lift and timing can be completed in 1~2 cycles. A set of combustion mode switching data is selected to show the response characteristics of the CDH-VVA mechanism. When switching from spark ignition (SI) to HCCI, it switches to HCCI combustion after only one combustion cycle and it switches to stable HCCI combustion after two combustion cycles, which proves the fast response characteristics of the CDH-VVA mechanism. At the same time, the CDH-VVA mechanism can form the intake port exhaust gas recirculation (EGR), as one type of internal EGR. This paper studies the HCCI combustion characteristics of the CDH-VVA mechanism in order to optimize it in the future and enable it to realize more forms of HCCI combustion. At 1000 rpm, if the maximum lift of the exhaust valve (MLEV) is higher than 5.0 mm or lower than 1.5 mm, HCCI combustion cannot operate stably, the range of excess air coefficient (λ) is largest when the MLEV is 4.5 mm, ranging from 1.0~1.5. Then, as the MLEV decreases, the range of λ becomes smaller. When the MLEV drops to 1.5 mm, the range of λ shortens to 1.0~1.3. The maximum value of the MLEV remains the same at the three engine speeds (1000 rpm, 1200 rpm and 1400 rpm), which is 5.0 mm. The minimum value of the MLEV gradually climbs as the engine speed increase, 1000 rpm: 1.5 mm, 1200 rpm: 2.0 mm, 1400 rpm: 3.0 mm. With the increase of engine speed, the range of indicated mean effective pressure (IMEP) gradually declines, 3.53~6.31 bar (1000 rpm), 4.11~6.75 bar (1200 rpm), 5.02~6.09 bar (1400 rpm), which proves that the HCCI combustion loads of the intake port EGR are high and cannot be extended to low loads. The cyclic variation of HCCI combustion basically climbs with the decrease of the MLEV and slightly jumps with the increase of the engine speed. At 1000 rpm, when the MLEV is 5.0 mm, the cyclic variation range is 0.94%~1.5%. As the MLEV drops to 1.5 mm, the cyclic variation range rises to 3.5%~4.5%. Taking the maximum value of the MLEV as an example, the cyclic variation range of 1000 rpm is 0.94%~1.5%, 1200 rpm becomes 1.5%~2.3% and 1400 rpm rises to 2.0%~2.5%.

Optimal Degree of Hybridization for Spark-Ignited Engines with Optional Variable Valve Timings

The electric hybridization of vehicles with an internal combustion engine is an effective measure to reduce CO2 emissions. However, the identification of the dimension and the sufficient complexity of the powertrain parts such as the engine, electric machine, and battery is not trivial. This paper investigates the influence of the technological advancement of an internal combustion engine and the sizing of all propulsion components on the optimal degree of hybridization and the corresponding fuel consumption reduction. Thus, a turbocharged and a naturally aspirated engine are both modeled with the additional option of either a fixed camshaft or a fully variable valve train. All models are based on data obtained from measurements on engine test benches. We apply dynamic programming to find the globally optimal operating strategy for the driving cycle chosen. Depending on the engine type, a reduction in fuel consumption by up to 32% is achieved with a degree of hybridization of 45%. Depending on the degree of hybridization, a fully variable valve train reduces the fuel consumption additionally by up to 9% and advances the optimal degree of hybridization to 50%. Furthermore, a sufficiently high degree of hybridization renders the gearbox obsolete, which permits simpler vehicle concepts to be derived. A degree of hybridization of 65% is found to be fuel optimal for a vehicle with a fixed transmission ratio. Its fuel economy diverges less than 4% from the optimal fuel economy of a hybrid electric vehicle equipped with a gearbox.

Reverse Engineering of Research Engine Cylinder-Head

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.

A Machine Learning Based Numerical Approach for Valve Seating Velocity Control in an Electromagnetic Camless System

Improving internal combustion engine performance is a significant concern over the past few decades for engine researchers and automobile manufacturers. One of the promising methods for improving the engine performance is variable valve actuation system with camless technology. In the camless system, the conventional spring-operated valve actuation mechanism is removed, and an actuator is used to independently control the valve events (lift, timing, and duration). Among different camless systems, electromagnetic variable valve actuation (EMVA) becomes more viable because of its faster valve operation. However, the major challenge is to control the valve seating velocity (velocity at which valve comes to rest during seating on the cylinder head) due to the absence of the cam mechanism. A sophisticated control system must be developed to achieve an acceptable valve seating velocity. In this study, a proportional-integral-derivative (PID) controller was used to control the EMVA system. A machine learning tool, i.e., genetic algorithm, and an iterative method, i.e., Ziegler-Nichols, were used to optimize the PID controller’s gain values. The valve lift profiles obtained using the Ziegler-Nichols method and the genetic algorithm were compared. It was found that the developed algorithm for the EMVA system can achieve faster rise time compared to the experimental results [25] utilized inverse square method. A parametric investigation was performed to verify the robustness of the PID controller with a change in temperature. It is concluded that the temperature rise may increase the resistance and inductance, but the controller with the updated gain values can control the EMVA system without affecting the performance parameter. The simulation was performed for both forward and backward strokes to investigate the valve seating velocity. It was found that the controller can achieve an acceptable valve seating velocity. Hence, the machine learning tool helps in optimizing the PID controller’s gain values to achieve faster valve operation with an acceptable valve seating velocity.

Computational studies of the influence of variable valve timing on the performance of a gas engine with Miller’s thermodynamic cycle

Current development trends in the field of internal combustion engines aim at regulating all processes of the engine and individual units. A converted diesel to gas engine with Miller thermodynamic cycle is more energy efficient at partial loads than a gas engine with Otto thermodynamic cycle. The Miller cycle engine with variable valve timing and valve lift has been investigated to improve performance and energy efficiency across the load range. The aim of the work is to study the influence of the displacement of the valve timing phases of the intake and exhaust camshafts and the valve lift height on the performance of the gas engine with the Miller cycle. Computer modelling was based on data obtained from the full-scale experiment on the gas engine with the Miller thermodynamic cycle.