Browse Topic: Variable valve timing
Oil pressure, the most fundamental to engine's performance and longevity, is not only critical to ensure that the engine components are properly lubricated, cooled, and protected against wear and contamination, but also ultimately contributing to reliable engine performance. Due to several factors of engine such as, rotational fluctuation, aeration, functioning of hydraulic components there are fluctuations in oil pressure. In engines, with a crank-mounted fixed displacement oil pump (FDOP), these inherited pressure fluctuations cannot be eliminated completely. However, it is very necessary to control the abnormal oil pressure fluctuation because abnormal pressure fluctuation may lead to malfunction of hydraulic component functioning like variable valve timing (VVT), hydraulic lash adjuster (HLA) and dynamic chain tensioner which can further cause serious issues like excessive or sudden load drops, unstable engine performance, valve train noise, improper valve lift operation etc. In this paper, engine oil pressure fluctuation in HLA gallery is studied, and its impact was assessed on valve train system. Root cause analysis (RCA) was conducted using high frequency oil pressure measurement to understand the various reasons impacting high oil pressure fluctuations inside HLA galleries. Time domain analysis was performed to understand oil pressure fluctuations with respect to VVT cam phasing. Angle domain analysis was performed to assess the impact of oil pressure fluctuations on valve train behavior. Further findings from this study aim to enhance the understanding of impact of VVT cam phasing in oil pressure fluctuations.
SAE J1939-73 defines the SAE J1939 messages to accomplish diagnostic services and identifies the diagnostic connector to be used for the vehicle service tool interface. Diagnostic messages (DMs) provide the utility needed when the vehicle is being repaired. Diagnostic messages are also used during vehicle operation by the networked electronic control modules to allow them to report diagnostic information and self-compensate as appropriate, based on information received. Diagnostic messages include services such as periodically broadcasting active diagnostic trouble codes, identifying operator diagnostic lamp status, reading or clearing diagnostic trouble codes, reading or writing control module memory, providing a security function, stopping/starting message broadcasts, reporting diagnostic readiness, monitoring engine parametric data, etc. California-, EPA-, or EU-regulated OBD requirements are satisfied with a subset of the specified connector and the defined messages.
Internal combustion engines must be individually tested at the end of the manufacturing process. In recent years classical hot test stands, where the engine is run for several minutes, are being replaced by cold test alternatives. The latter allow fast testing cycles using an external motoring device without using any fuel. The absence of fuel and combustion lowers the health and safety requirements for the plant itself and subsequent engine transport, but this comes at the cost of additional difficulties for the verification of the correct assembly and operation of the combustion system hardware. This paper presents a cold test concept, which includes dedicated measurements and algorithms for the detection of common failures in the manufacturing process, including those of the combustion hardware. Between other parameters, the test stand evaluates the existence of compression leaks, the correct variable valve timing (VVT) phasing, the operation of the ignition coils and injectors, and verifies the spark plugs gap to be within specifications. In all cases, non-intrusive sensors are used and the installation is done taking advantage of the standard wiring of the engine. Compression leaks are detected using the motoring torque and engine speed, and performing a frequency domain analysis of the signal; VVT phasing is verified by camshaft and crankshaft encoders, and with the recognition of the pulsation of the pressure in the manifolds; for the case of ignition coils and injectors, the system is electrically actuated and pattern recognition is applied to the intensity profile; finally, spark plug gap is inferred from the spark success rate at different energizing times.
In order to stand apart from the competition, there is an ever growing demand in Indian commercial vehicle segments to reach higher fuel economy while achieving the emission goals set by the BS-VI norms. With emissions standard set by BS-VI, novel techniques to improve fuel efficiency have to be considered that have least impact with respect to NOx and soot emissions. The optimization of exhaust and intake valve lifts with respect to engine speed, technology commonly known as Variable Valve Lift and Timing (VVT/VVL), has been implemented in many passenger vehicles propelled by gasoline engine. The aim of this work is do initial assessment of utilizing the VVL method on a LMD commercial vehicle diesel engine. A 3.8 litre BS-VI turbocharged EGR engine is used for this study. Valve lift and timing optimization for better fuel efficiency at rated power engine speed is carried out by using one-dimensional thermodynamic simulation software AVL BOOST. For this purpose, complete engine from intake to exhaust is modelled in the simulation software and base performance calibrated with the engine test bed data. Early Intake Valve Closing (EIVC) showed BSFC improvement for rated power engine speed at full and part load conditions. The EIVC valve lift optimized at this stage is further subjected to structural optimization with respect to valve-train dynamic and kinematic characteristics using AVL Excite. Based on the optimized EIVC valve lift characteristics a new cam profile is prepared using ISAC method and the same is carried forward for proto development to carry out POC on engine test dynamometer. The results from test bed showed improvement in BSFC which was in-line with prediction of the simulation model.
Today the whole automotive world is progressively transforming towards the adoption of new alternate, advanced and innovative technologies evolving in ICE and Vehicle technology to meet the stringent emission regulations and future CO2 goals while protecting the environment. May it be Engine downsizing, Down speeding, Cylinder deactivation, VCR, VVT, Dynamic Skip Fire (DSF), Alternate fuels, Alternate materials, Steel pistons, Advanced thermal barrier/coating technology, Electrification or Various degrees of hybridization. The key to achieve better FE or reduction in CO2 emissions is realized by saving every pie of energy spent or reducing the parasitic losses and improving overall engine efficiencies wherever possible. In this paper, an experimental study on the deployment of various energy saving technologies, concepts are exploited on small 2 cylinder common rail BSVI engine for friction reduction and efficiency improvements while moving forward from BSIV to BSVI legislation phase. It has been demonstrated in this experiment that the whole package of friction reduction on an engine saves the engine FHP energy by 15% over the base BSIV engine. The deployment of such technologies not only improves mechanical efficiency of BSVI engine by 5.43 % over the base BSIV engine configuration but also substantial improvement in engine performance and efficiencies with an average benefit of 4.6 % in BSFC over the base engine along with FE benefit when tested on vehicle.
SAIC Motor has developed an all new 2.0 L 4-cylinder turbocharged gasoline direct injection engine to meet the market demand and increasingly stringent requirement of CAFE and tail-pipe emission regulations. A series of advanced technologies have been employed in this engine to achieve high efficiency, high torque and power output, fast response low-end torque performance, refined NVH performance, all at market leading level, and low engine-out emissions. These main technologies include: side mount gasoline direct injection with 35MPa fuel injection system, integrated exhaust manifold, high tumble combustion system, 2-step intake variable valve lift (DVVL) with Miller Cycle, efficient turbo charging with electric wastegate (EWG), light weight and compact structural designs, NVH measures including balancer system with silence gear, friction reduction measures, optimized thermal management, etc. As a result of application of these technologies and optimized designs, the engine is able to achieve over 39.5% maximum brake thermal efficiency (BTE), as well as large high efficiency region in the fuel map that covers most typical customer real driving conditions. It delivers 360 Nm maximum torque from 1500RPM to 4000RPM, and 172kW rated power at 5500RPM, with fast low end torque response. The new 2.0T engine already started the mass production in October, 2020, with its first application in ROEWE iMAX8, a MPV. Even with the weight of 2058kg, the vehicle is able to achieve 9.3s 0-100km acceleration, while meeting China VI b standard emission regulatory requirement equipped with this new 2.0T engine. In this paper, the design/optimization of the engine systems will be described. The detailed investigations with simulations and dyno testing of effects of the core technologies will also be presented.
The EU recently decided to reduce CO2 emissions of commercial vehicle fleets by 30% until 2030. One possible way to achieve this target is to convert commercial vehicle diesel engines into stoichiometric natural gas engines. Based on this, a commercial vehicle single cylinder diesel engine with variable valve actuation and high-pressure EGR is converted into natural gas operation to increase efficiency and thus reduce CO2. Additionally, a water injection system is integrated. All three technologies are investigated on their own and in combination. To reduce longer combustion durations caused by Miller valve timing and charge dilution, a piston bowl with extra high turbulence generation is designed. Additionally, a swirl variation is carried out. The results show, that high swirl motion and high turbulence can lead to a disadvantage in efficiency despite faster combustion durations due to higher wall heat losses. However, by using suitable combinations, it is possible to minimize throttle losses in low load operation and achieve optimum combustion locations (8°CA aFTDC) at full load operation with conventional compression ratios (ε=12). This allows for an increase in geometric compression ratio and thus in efficiency. Efficiency improvements of over 2 %-points have been achieved at full load with common natural gas (MN ~81.5). This helps to fulfil future CO2/NOx legislations for HD commercial vehicle engines.
An experimental study was conducted on a multi-cylinder engine to understand the feasibility of a six-stroke homogeneous charge compression ignition (HCCI) operation under stoichiometric conditions. State-of-the-art technologies such as continuously variable valve duration (CVVD) and high-pressure gasoline direct injection (GDI) were experimentally exploited to increase the degree of freedom of engine control. The motivation of six-stroke HCCI combustion is to remedy the load limitation and the cyclic variation in four-stroke HCCI combustion with two additional strokes: compression and expansion strokes. The six-stroke HCCI combustion occurs in the following order. First, hot residual gas is trapped by applying negative valve overlap (NVO). Next, fresh air enters, fuel is injected, and lean HCCI combustion occurs in the 1st power stroke (PS). Subsequently, additional fuel is injected, and the 2nd combustion occurs with the remaining oxygen in the two additional strokes. In this study, we discuss the effect of various control variables, i.e., fuel split ratio, and injection timings, on the combustion phases of the two power strokes. In addition, we present the challenge of achieving proper combustion phasing in stoichiometric six-stroke HCCI operation, mainly in high load operation when we intend to split the load. As the load is more distributed to the 1st PS, it may lead to a significantly high mixture temperature at the beginning of the 2nd PS, which can result in a premature 2nd combustion phase. We discuss how the aforementioned control variables can be utilized to mitigate the challenge.
Natural gas has been used in spark-ignition (SI) engines of natural gas vehicles (NGVs) due to its resource availability and stable price compared to gasoline. It has the potential to reduce carbon monoxide emissions from the SI engines due to its high hydrogen-to-carbon ratio. However, short running distance is an issue of the NGVs. In this work, methodologies to improve the fuel economy of a heavy-duty commercial truck under the Japanese Heavy-Duty Driving Cycle (JE05) is proposed by numerical 1D-CFD modeling. The main objective is a comparative analysis to find an optimal fuel economy under three variable mechanisms, variable valve timing (VVT), variable valve actuation (VVA), and variable compression ratio (VCR). Experimental data are taken from a six-cylinder turbocharged SI engine fueled by city gas 13A. The 9.83 L production engine is a CR11 type with a multi-point injection system operated under a stoichiometric mixture. For minimizing optimal valve strategy selections and engine testing procedures, a one-dimensional engine model is developed in GT-Power software using experimental data and engine specifications provided by a project partner. The model is built using the same theory as of spark-ignition engines. Knock prediction is based on the Shell model, and a spark timing optimization logic is coupled to the model. In-cylinder pressure, rate of heat release, brake mean effective pressure, and maximum brake torque spark ignition timings are well reproduced, as compared with that of 12 experimental operating points under engine speed and load variations. In order to build a baseline brake specific fuel consumption (BSFC) map in the driving cycle, the simulation model is used to generate 51 BSFC points, as proposed in the JE05 cycle under speed-torque changes. From the baseline engine model, the average fuel economy of the heavy-duty natural gas truck is 4.14 km/L. 0.5 % and 2.43% of simulated fuel economy improvements are found when the engine is operated under VVT and VVA mechanisms (fixed lifts), respectively. Significant fuel economy improvement is achieved at about 6.31% under VCR engine operation compared with the baseline engine model.
The tests were carried out on an 3D engine model with an unconventional multiple linkage system. Compared to a classic crankset, the mechanism consists of more elements. In this multiple linkage system the camshaft, the piston rod and the main rod are connected to one common element. The camshaft rotating during operation at twice the speed of the crankshaft makes possible to achieve different piston stroke lengths with each revolution. With proper synchronization of the camshaft revolution with the crankshaft, the suction and compression stroke is smaller in relation to the expansion and exhaust strokes. For this reason, the Atkinson cycle was obtained without interfering with the variable valve timing. The thermal cycle is characterized by increased theoretical thermal efficiency. Due to the unique mechanism, the piston movement has different characteristics compared to classic solutions. Therefore, work was undertaken to analyze the distribution of forces in the system. For the needs of the work, a 3D model of the described engine was created. It was used to examine the characteristics of the piston path during operation. Using computer simulation, piston movement and forces occurring in the system were analyzed. Numerical simulations of combustion process were also carried out in a program designed for internal combustion engines. The most important thermodynamic indices such as pressure distributions, temperatures and heat release are presented. Identical tests were also carried out for the engine with a conventional crank system. The results of both engines were combined and analyzed.
SAE J1939-73 defines the SAE J1939 messages to accomplish diagnostic services and identifies the diagnostic connector to be used for the vehicle service tool interface. Diagnostic messages (DMs) provide the utility needed when the vehicle is being repaired. Diagnostic messages are also used during vehicle operation by the networked electronic control modules to allow them to report diagnostic information and self-compensate as appropriate, based on information received. Diagnostic messages include services such as periodically broadcasting active diagnostic trouble codes, identifying operator diagnostic lamp status, reading or clearing diagnostic trouble codes, reading or writing control module memory, providing a security function, stopping/starting message broadcasts, reporting diagnostic readiness, monitoring engine parametric data, etc. California-, EPA-, or EU-regulated OBD requirements are satisfied with a subset of the specified connector and the defined messages.
The present paper aims at developing a novel methodology to create a one-dimensional simulation model for an automotive turbocharged gasoline engine. The gas-path modeling of the engine, which includes a variable nozzle turbine (VNT) and variable valve timing (VVT) strategies, is described in detail. The model calibration procedure is mainly distinguished by isolating the different engine parts, decoupling the turbocharger, using PI controls to find fitting parameters and checking and validating mean and crank-angle resolved variables. To handle model limitations, it requires experimental data and a previous combustion analysis of some steady operating points. The methodology is completed with the determination of fitting correlations to estimate heat losses and pressure drops in engine systems. It also includes the training of an Artificial Neural Network (ANN) to predict the combustion process and the integration into the model and final validation. This validation is performed not only in steady state engine conditions but also in transient operation with EGR.
In recent years gasoline compression ignition (GCI) has been shown to offer an attractive combination of low criteria pollutants and high efficiency. However, enabling GCI across the full engine load map poses several challenges. At high load, the promotion of partial premixing of air and fuel is challenging due to the diminished ignition-delay characteristics at high temperatures, while under low load operations, maintaining combustion robustness is problematic due to the low reactivity of gasoline. Variable valve actuation (VVA) offers a means of addressing these challenges by providing flexibility in effective compression ratio. In this paper, the effects of VVA were studied at high loads in a prototype heavy-duty GCI engine using a gasoline research octane number (RON) 93 at a geometric compression ratio (CR) of 15.7. Both late intake valve closing (LIVC) and early intake valve closing (EIVC) strategies were analyzed as a measure to reduce the effective compression ratio. For the analysis, a close-coupled GT-Power based 1-D engine simulation with a 3-D CFD modeling methodology was used. The analysis was performed on the B-speed engine load conditions B25, B50 and B75, derived from the heavy-duty Supplemental Emissions Test (SET) cycle. EIVC was shown to have a greater impact on reducing effective compression ratio than LIVC, but at the expense of higher gas exchange, or pumping, losses. With increasing load, the effect of the LIVC strategy on compression ratio gradually diminished, because the reverse flow through the intake valve was reduced. Overall, the charge temperature and pressure were reduced linearly with EIVC, whereas retarding LIVC showed an exponential rise in temperature and pressure. The simulated combined efficiency for the stock turbocharger deteriorated with both the EIVC and LIVC approach.
Items per page:
50
1 – 50 of 481