Exhaust Valve Timing Research Articles

Turbulent Premixed Combustion in SI Engine

The turbulent lean premixed combustion simulation is implemented in 4- stroke spark ignition (SI) engine. The Turbulent Flame speed Closure model (TFC) is used in different turbulent flow conditions. The model is tested for a variety of flame configurations such as turbulent flame speed, the heat release from the combustion and turbulent kinetic energy in the radial direction of the cylinder at 15.5 mm below the top dead center TDC point. The simulation performs in the three cases of the (intake / exhaust) valve timing. The exhaust valve case is an essential leverage on the turbulent flame specification. The combustion period is very important factor in SI engine which is controlled especially by the turbulent flame speed. The turbulent flame speed and heat transfer is ascendant less than 10 % and 3% in case of intake and exhaust valves are closed respectively. Moreover, the results show that the brake power enhances less than 4% and more than 40% with increase fuel temperature 60 K and engine speed 3000 rpm respectively.

Mechanism study of scavenging process and its effect on combustion characteristics in a boosted GDI engine

The scavenging process is helpful to suppress super-knock in a 4-stroke turbocharged gasoline direct injection engine because it can reduce in-cylinder thermal load and clear the suspending residual particles from previous cycles. This paper investigated the effects of dual variable valve timing on scavenging and combustion process by simulation and experimental study. The simulation results showed that the scavenging process improved with the advance of intake valve timing and the retard of exhaust valve timing. When the valve overlap duration was the same, the early occurrence of valve overlap was helpful to the scavenging process. The longer the valve overlap duration was the better the scavenging process would be. When exhaust valve timing was fixed, spark timing retarded with the advance of intake valve timing, nevertheless, the mixture mass, basic specific fuel consumption rate, combustion duration, and exhaust temperature increased with the advance of intake valve timing. In two early intake valve timing conditions, when exhaust valve timing was retarded, the mixture mass, basic specific fuel consumption, exhaust temperature raised, combustion duration and the length of ignition delay shortened. In three late intake valve timing conditions, the combustion characteristics were unchanged with the postponement of exhaust valve timing. The effect of dual variable valve timing on scavenging and combustion process was similar. Intake valve timing played a determinate role in the combustion performance of gasoline direct injection engine. The optimized scavenging process could lower the super-knock frequency and improve combustion characteristics.

Global optimization of the diesel engine–organic Rankine cycle (ORC) combined system based on particle swarm optimizer (PSO)

The organic Rankine cycle (ORC) system powered by exhaust heat has great potential in improving engine performance. Many optimizations of the only ORC system were conducted, while the existing literature pays limited attention to the optimization of the engine–ORC combined system. By considering the importance of interaction, cooperation, and influence between the engine and ORC system, a global optimization of the diesel engine–ORC combined system (herein, the combined system) is conducted in this paper with respect to power output and fuel economy. A GT-Suite model of the combined system and a GT-Suite/Simulink co-simulation model are proposed to obtain the optimum operating parameters of the engine and the ORC system under various operating conditions. Furthermore, the effects of the operating parameters, namely, exhaust valve timing, injection timing, expander speed, and pump speed, are evaluated on the combined system. In addition, models of the engine and the ORC system are calibrated, and a particle swarm optimizer (PSO) is designed and adopted for global optimization. Optimization results show improvements of 3.24% and 3.13% on the power output and brake specific fuel consumption (BSFC), respectively, with full engine load when the engine is operated at 3600 r/min. In the optimization of fuel economy with partial engine load, a maximum reduction of 5.71% on the BSFC of the combined system is obtained at 3600 r/min engine speed.

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.

Optimum shape design of a BLDC motor for electric continuous variable valve timing system considering efficiency and torque characteristics

Recently, environmental problems caused by global warming and exhaust gas have been increasing, leading governments all over the world to implement strict environmental regulations. For this reason, the automotive industry has begun working to increase fuel efficiency and reduce emissions. In addition, in order to improve the performance of engines implemented in internal combustion engines (ICEs) and hybrid electric vehicles (HEVs), electronic control actuators are becoming increasingly preferred over conventional mechanical parts. In particular, engine intake and exhaust valve timing techniques are critical to improving fuel economy and reducing vehicle emissions. Previously, a hydraulic continuous variable valve timing (CVVT) system was used for valve timing control. However, a disadvantage of this type of system is that the response speed is slow at low and high engine temperatures; these conditions limit the extent of automobile fuel efficiency improvement. Therefore, an electric variable valve timing system (E-CVVT) is being studied to overcome this disadvantage. In this paper, we propose a shape optimum design method for brushless DC (BLDC) motors used in an electric continuous variable valve timing (E-CVVT) system, which is employed in ICEs and HEVs. The proposed design aims to maximize the maximum torque and rated efficiency of BLDC motors, and minimize cogging torque. To select the optimal design variables, we chose to implement Latin hypercube sampling (LHS) to avoid duplication of sampling points. The characteristics of the sampling points obtained via the LHS method were calculated by using finite element (FE) analysis. In order to consider the nonlinearity of properties, we have created an approximate modeling technique that uses a radial basis function. Finally, genetic algorithms were used to determine the design parameters of the optimum model. The effectiveness of the proposed BLDC motor design process is verified by comparing the FE analysis and experimental results. Simulation and experimental results confirmed that the proposed optimized design procedure yields improved operating characteristics. Specifically, testing the proposed optimized design yielded a 16.7% increase in the maximum torque, and a 66.2% reduction in the cogging torque. In addition, the vehicle test confirmed that the proposed design was suitable for an E-CVVT system equipped with a BLDC motor. In addition, the optimum model of the BLDC motor was applied to the E-CVVT system. The response characteristics of the conventional hydraulic CVVT system and E-CVVT were compared via vehicle testing. The response speed of the E-CVVT system was 0.65 s faster than that of the CVVT system during the retard angle phase. Therefore, it was a 39.4% improvement in the response performance.

Exhaust Tuning of an Internal Combustion Engine by the Combined Effects of Variable Exhaust Pipe Diameter and an Exhaust Valve Timing System

Changes to engine geometry and specifications can produce better torque, power, volumetric efficiency and more. The technique known as wave tuning can lead to better engine torque and power. This paper focuses on increasing the engine torque by improving the exhaust fluid flow through the exhaust manifold. Phasing and intensity of the pressure waves in the exhaust manifold have significant effects on scavenging, valve overlapping and pumping losses. In this research, individual and combined effects of variable exhaust runner diameter and exhaust valve timing on the fluid flow from exhaust of the engine are studied using computer simulation. An engine simulation software, Ricardo Wave, is utilized in this research. The analysis is conducted on a 1-D model of a KTM 510 cc single cylinder, four-stroke Sl engine. The data gathered shows that varying only the exhaust pipe diameter continuously with speed yields an average of 4.23% improvement in torque from the original engine model. However, due to practical constraints, the diameter is limited to vary in three steps (36 mm, 45 mm and 60 mm). This has reduced the average improvement of torque to 3.78%. Varying the valve timing alone gains an average of 1.94% improvement in torque. Varying both the exhaust pipe diameter in three steps and the exhaust valve timing yields an average of 4.69% improvement in torque. This average is conducted over the engine speed ranges from 2000 to 11,000 rpm.

ADVANCED NUMERICAL AND EXPERIMENTAL STUDIES ON CI ENGINE EMISSIONS

In these studies, three important works examined to get ultra-low emission for a single cylinder diesel engine. The first study was performed for single fuel and compression ratio (CR), intake and exhaust valve timings, mass flow rate were optimized for a range of engine speed. Then for the same engine injection parameters such as start of injection (SOI), injector cone angle, and split injection structures were examined to get optimum parameters for the diesel engine. In CR studies, different combustion chambers were tested according to injector cone angles and fuel-wall interaction. In the second study, in addition to the above studies, dual fuel compressed biogas (CBG) and diesel combustion were analyzed under different engine loads both experimentally and computationally. Optimized single fuel diesel cases were compared with CBG + Diesel dual fuel cases which employed port injection for CBG fuel. In dual fuel engine applications, CBG fuel and air mixture is induced from intake port and this air-fuel mixture is ignited by pilot diesel fuel near top dead center (TDC). In dual fuel engine mode, exhaust emissions reduced considerably especially in NOx and particulate matter (PM) because of methane (CH4) rate and optimized engine parameters. The third study is focused on aftertreatment systems to minimize residual exhaust emissions. The emissions of the diesel engines consist of various harmful exhaust gases such as carbon monoxide (CO), particulate matter (PM), hydrocarbon (HC), and nitrogen oxides (NOx). Several technologies have been developed to reduce diesel emissions especially NOx reduction systems in last decades. The most promising NOx emission reduction technologies are exhaust gas recirculation (EGR) system to reduce peak cylinder temperature that reduces NOx form caused by combustion and active selective catalyst reduction (SCR) system using reducing agent such as urea-water-solution for exhaust aftertreatment system. In this study, computational fluid dynamic (CFD) methodology was developed with conjugate heat transfer, spray, deposit and chemical reaction modeling then emission prediction tool was developed based on the CFD results with deposit prediction mechanism. CFD and deposit results were correlated with image processing tool in flow test bench.

Influence of exhaust residuals on combustion phases, exhaust toxic emission and fuel consumption from a natural gas fueled spark-ignition engine

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.

Effects of intake and exhaust valve timing on the performance of an air‐powered rotary engine

This work is aimed at improving the performance of the air‐powered rotary engine. A dynamic simulation model which includes an eccentric motion and rotary valve movement was established by our particle image velocimetry (PIV) experimental data. Then the power and specific steam consumption (SSC) was evaluated. The pressure distribution in the chamber was obtained which was difficult to obtain through experiment. Simulation results showed that for the work process and pressure distribution, the intake valve timing mainly affected the intake expansion stage (A2) and pure expansion stage (B). Due to this, a relatively low pressure was distributed in the middle of the chamber and this was beneficial to the intake and work processes. The exhaust valve timing mainly affected the exhaust stage (C) and initial intake stage (A1). Therefore, a relatively high pressure which was distributed in the middle‐rear of the chamber was beneficial to the exhaust processes. For the power and SSC, the power increased initially then decreased and the SSC decreased with the increase of intake advance angle respectively. Both the power and the SSC increased with the increase of intake duration angle. The power increased while the SSC decreased with the increase of exhaust advance angle. The power increased and the SSC decreased initially then increased with the increase of exhaust duration angle. The preferred parameters were found to be 30° CA, 240° CA, 30° CA, and 280° CA. These improved parameters had a 2.7% increase in the power and also a 2.4% decrease in the SSC. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1462–1474, 2018

Investigation on the Effect of the Gas Exchange Process on the Diesel Engine Thermal Overload with Experimental Results

In this paper, the influence of the gas exchange process on the diesel engine thermal overload is provided. Main components involved in the gas exchange process are discussed. The ambient conditions, the turbocharger performance, and the valve timing that affect the gas exchange process have been investigated. Experiments were conducted to simulate ambient conditions at different geographical locations and demonstrated a decrease in oxygen concentration in the exhaust as the humidity level in the air increased. Additionally, the effect of an inefficient turbocharger on an engine operating at part-load was also investigated. It was observed that an overly lean air/fuel mixture caused inefficient scavenging and the corresponding level of residual gas trapped in the cylinder increased. This resulted in partial combustion which could be observed as white smoke from the engine exhaust stack, therefore indicating the presence of unburnt fuel. Exhaust valve timing measurements showed that the cylinder with the highest wear rate had its valve closure timing 10 crank angle degrees after the cylinder with least wear rate. The exhaust valves were closed earlier than the designed condition which impaired the scavenging process and increased the level of residual gas trapped in the cylinder. This resulted in a reduction of the actual air-to-fuel ratio and high exhaust gas temperatures.

Model-based multi-objective Pareto optimization of the BSFC and NOx emission of a dual-fuel engine using a variable valve strategy

Various advanced technologies, including dual-fuel combustion, have been developed to meet reinforced emission regulations in the automobile industry. In this work, natural gas (NG) was added from 0 to 30% in steps of 10% as the energy fraction of the fuel to evaluate the fundamental effects of the NG substitution ratio (NSR) on the combustion, performance and nitrogen oxides (NOx) emission of a dual-fuel engine. Although the NOx emission significantly improved because of the higher specific heat capacity of air–NG mixtures, the in-cylinder pressure decreased with increasing NG fraction because of a longer ignition delay, which also detrimentally affected the brake specific fuel consumption (BSFC) by decreasing the brake thermal efficiency (BTE) of the engine. The injection timing was optimized using a design of experiments (DoE) approach to minimize the BSFC under various load and NSR conditions. The optimal injection timing was more advanced with lower load and higher NSC conditions. Additionally, the optimal Pareto fronts for improved performance and NOx emission of the dual-fuel engine were obtained from a multi-objective Pareto optimization. These results suggested suitable intake and exhaust valve timing strategies to control the BSFC and NOx emission of a dual-fuel engine.

Research on the Optimization Design of Motorcycle Engine Based on DOE Methodology

The optimization design of engine is always one of the top concerns in motorcycle industry. In this paper, effective torque and fuel consumption ratio are defined as the performance evaluation indexes of engine, while air-fuel ratio, intake valve timing angle, exhaust valve timing angel, pressure, and temperature are defined as input variables. With the application of DOE methodology, a full factorial DOE is conducted to estimate the regression model and identify the statistical significant factors. And then, with the selection of additional experimental points, RSM is introduced to construct the precise regression model between input variables and performance indexes. Based on that, an optimum solution that can satisfy both performance requirements are brought forward and testified.

ANALYSIS OF EXHAUST GAS EMISSION IN THE MARINE TWO-STROKE SLOW-SPEED DIESEL ENGINE

This paper explores the problem of exhaust emissions of the marine two-stroke slow-speed diesel engines. After establishing marine diesel engine regulations and defining the parameters influencing exhaust emissions, the simulation model of the marine two-stroke slow-speed diesel engine has been developed. Furthermore, the comparison of numerical and experimentally obtained data has been performed, resulting in achieving the model validity at 100% load, which represents a requirement for further exhaust gas analysis. Deviations obtained at the real engine and the model range from 2% to 7%. An analysis of the influential parameters such as compression ratio, exhaust valve timing and fuel injection timing has been performed. The obtained results have been compared and conclusions have been drawn.

EFFECT OF CYLINDER DEACTIVATION STRATEGIES ON ENGINE PERFORMANCES USING ONE-DIMENSIONAL SIMULATION TECHNIQUE

In order to meet consumer and legislation requirements, big investments on key technology strategies have been made to ensure fuel consumption is reduced. Recent technologies for gasoline engines are lean combustion technologies (including direct injection and homogenous charged compression ignition), optimizing intake and exhaust valve timing with valve lift and also cylinder deactivation system (CDA) have been practised to improve the engine efficiency. The purpose of this study is to investigate the engine behavior when running at different cylinder deactivation (CDA) strategies. One-dimensional engine model software called GT-Power is used to predict the engine performances. Five strategies were considered namely normal mode, spark plug off mode, cylinder deactivation mode, intake normal with exhaust off mode, and intake off with exhaust normal mode. Engine performance outputs of each strategy are predicted and compared at BMEP of 3 bars with engine speed of 2500 rpm. Also, the effect of CDA strategies on in-cylinder pressure and pumping loss are performed. The study shows that all of these cylinder deactivation strategies are capable of reducing the pumping loss (PMEP) and fuel consumption, thus increasing the thermal efficiency of the engine. The results suggest that the most beneficial strategy for activating CDA is for the case whereby both the intake and exhaust valves are kept closed. This CDA mode capable of increasing brake thermal efficiency up to 22% at entire engine speeds operation. This strategy successfully reduced the BSFC. It was found that most of these cylinder deactivation strategies improve the engine performance during part load engine condition

Effects of valve timing, valve lift and exhaust backpressure on performance and gas exchanging of a two-stroke GDI engine with overhead valves

The current demand for fuel efficient and lightweight powertrains, particularly for application in downsized and hybrid electric vehicles, has renewed the interest in two-stroke engines. In this framework, an overhead four-valve spark-ignition gasoline engine was modified to run in the two-stroke cycle. The scavenging process took place during a long valve overlap period around bottom dead centre at each crankshaft revolution. Boosted intake air was externally supplied at a constant pressure and gasoline was directly injected into the cylinder after valve closure. Intake and exhaust valve timings and lifts were independently varied through an electrohydraulic valve train, so their effects on engine performance and gas exchanging were investigated at 800rpm and 2000rpm. Different exhaust backpressures were also evaluated by means of exhaust throttling. Air trapping efficiency, charging efficiency and scavenge ratio were calculated based on air and fuel flow rates, and exhaust oxygen concentration at fuel rich conditions. The results indicated that longer intake and exhaust valve opening durations increased the charge purity and hence torque at higher engine speeds. At lower speeds, although, shorter valve opening durations increased air trapping efficiency and reduced the estimated supercharger power consumption due to lower air short-circuiting. A strong correlation was found between torque and charging efficiency, while air trapping efficiency was more associated to exhaust valve opening duration. The application of exhaust backpressure, as well as lower intake/exhaust valve lifts, made it possible to increase air trapping efficiency at the expense of lower charging efficiency.

Development and validation of electro-hydraulic camless free-piston engine

The scavenging system in two stroke engine is very important, therefore an electro-hydraulic camless variable valves actuation is developed and the effect of the exhaust valve character change on HFPE engine performance is investigated. Firstly the HFPE working principle and the control strategy are analyzed, and then a 3D CFD model is built by AVL_FIRE software, the piston displacement is obtained by 0D simulation. The simulation results are verified by the ideal scavenging model. The specific distributions of flow field are by plane cut. Further the scavenging parameters, such as trapping ratio, delivery ratio and scavenging efficiency, are analyzed with different intake pressure. In order to optimize the scavenging performance, the scavenging efficiency is affected by intake port height and the exhaust valve timing. Therefore the laws of higher scavenging efficiency are obtained. Experiment is necessary for validating the electro-hydraulic camless variable valves actuation system design. The specific prototype test bench is introduced for experimental study. In addition, the factors that affect variable valves actuation system are tested. Finally, the engine operation results are obtained and the engine performance is analyzed further.

Multi-objective optimization of a natural aspirated three-cylinder spark ignition engine using modified non-dominated sorting genetic algorithm and multicriteria decision making

The main purpose of this study is to find a special set of filling and emptying parameters of a three-cylinder engine, including geometrical design of intake manifold, intake and exhaust valve timing as design variables of the multi-objective optimization problem, which lead to the best values of BSFC (Brake Specific Fuel Consumption), and torque of the engine at all working speeds as four separate objective functions. The modified Non-dominated Sorting Genetic Algorithm (NSGA-II), which is an evolutionary Pareto-based method, is used as the optimization algorithm, and the technique for order of preference by similarity to ideal solution is used as a Multi-Criteria Decision Making Method to select the trade-off design based on different design strategies through the design vectors which are proposed. Group Method of Data Handling-type of Artificial Neural Networks is used to predict the relation between the design variables and the objective functions based on a 243-sized set of samples, which are chosen by Factorial method, and the corresponding engine designs are simulated using GT-SUITE as an Engine Simulation Software. The method of simulation is verified by comparison of experiment and simulation results. The verification process shows that the engine simulation code could predict the engine's performance by 4.78% error. Convergence and start point independence of the optimization algorithm (modified NSGA-II) is also investigated. The final results show remarkable improvement in BSFC and torque at 3500 RPM and mean value of BSFC at all working speeds along with a small reduction in mean value of the engine's torque at all working speeds compared to corresponding characteristics of a similar three-cylinder engine.

Fuel Efficiency Optimization for a Divided Exhaust Period Regulated Two-Stage Downsized Spark Ignition Engine

In our previous paper, a new gas exchange concept termed divided exhaust period regulated two-stage (DEP R2S) system has been proposed. In this system, two exhaust valves in each cylinder are separately functioned with one valve feeding the exhaust mass flow into the high-pressure (HP) manifold, while the other valve evacuating the remaining mass flow directly into the low-pressure (LP) manifold. By adjusting the timing of the exhaust valves, the target boost can be controllable while improving the engine's pumping work and scavenging is attainable which results in better fuel efficiency from the gas exchange perspective. This paper will continue this study by adding an appropriate knock model to examine the benefits this concept could bring to the combustion phasing. The results at full load showed that under knock limited spark advance (KLSA) and fully optimized exhaust valve timing condition, the DEP R2S system benefited from lower pumping loss and better scavenging due to the reduced backpressure and improved pulsation interference despite suffering from reduced expansion ratio and expansion work. The combustion phasing was advanced across the engine speed which is mainly attributed to the reduced residual and the reduced requirement of gross indicated mean effective pressure (IMEP). The net brake-specific fuel consumption (BSFC) was observed to improve by up to 3% depending on the engine operating points. At part load, the DEP R2S system could be used as a mechanism to extend the “duration” of the exhaust valve. This will reduce the recompression effect of the exhaust residuals during the beginning and the end of the exhaust stroke compared to the original R2S model with late exhaust valve opening and early exhaust valve opening. In addition, increased internal exhaust gas recirculation (EGR) due to the increased overlap between the LP and the intake valve is also beneficial for the improved pumping mean effective pressure (PMEP) as the throttle can be further opened to reduce the corresponding throttling loss. The average net BSFC improvement is expected to be approximately 6–7%.

Research on the Effect of ETCI Based HCCI Technology in the Best Fuel Area

Exhaust check point injection compression ignition (ETC� ), the trapped promote internal thermal residues high temperature high pressure jet fuel mixture is one of the most effective methods to achieve homogeneous charge compression ignition (HCCI). This paper is based on the ETCcombustion mode to study the effect of timing heating of the exhaust valve and the cooling effect of the pressure on the combustion process.. Results show that the best fuel economy can start injection of Ca BTDC at 1500r/min, the exhaust valve timing on combustion properties are strongly influenced by the 370, Shan'xi. Using the residual gas coefficient of the exhaust valve timing control, the combustion stage can be controlled indirectly by the intake temperature of the cylinder. In addition, constant pressure, inlet pressure increasing can increase the excess air coefficient decrease the mixture of average air temperature, which can also be control as the key parameters of the combustion phase in some areas. Therefore, the reasonable cooperation between the exhaust valve timing and the pressure pressure can effectively control the combustion process and emission minimization. At 1500r / min, 30 (calcium negative valve overlap (NVO) and 0.18 MPa pressure, the limit of low load and high load limit of HCCI combustion can be reached 0.27 MPa and 0.723 MPa, respectively.

High load performance and combustion analysis of a four-valve direct injection gasoline engine running in the two-stroke cycle

With the introduction of CO2 emissions legislation or fuel economy standards in Europe and many countries, significant effort is being made to improve spark ignition gasoline engines because of their dominant market share in passenger cars and potential for better fuel economy. Amongst several approaches, the engine downsizing technology has been adopted by the automotive companies as one of the most effective methods to reduce fuel consumption of gasoline engines. However, aggressive engine downsizing is constrained by excessive thermal and mechanical loads as well as knocking combustion and low speed pre-ignition (also known as super-knock). In order to overcome such difficulties, a gasoline direct injection single cylinder engine was modified to run under the two-stroke cycle by operating the intake and exhaust valves around bottom dead centre (BDC) at every crankshaft revolution. The combustion products were scavenged by means of a reversed tumble flow of compressed air during the positive valve overlap period at BDC. The engine output was determined by the charging and trapping efficiencies, which were directly influenced by the intake and exhaust valve timings and boost pressures. In this research a valve timing optimisation study was performed using a fully flexible valve train unit, where the intake and exhaust valve timings were advanced and retarded independently at several speeds and loads. A supercharger was used to vary the load by increasing the intake pressure. The effects of valve timing and boost pressure in this two-stroke poppet valve engine were investigated by a detailed analysis of the gas exchange process and combustion heat release. Gaseous and smoke emissions were measured and analysed. The results confirmed that the two-stroke cycle operation enabled the indicated mean effective pressure to reach 1.2MPa (equivalent to 2.4MPa in a four-stroke cycle) with an in-cylinder pressure below 7MPa at an engine speed as low as 800rpm. The engine operation was limited by scavenging inefficiencies and short time available for proper air–fuel mixing at high speeds using the current fuel injector. The large amounts of hot residual gas trapped induced controlled auto-ignition combustion at high speeds, and thus the abrupt heat release limited higher loads.