Browse Topic: Chokes
Tractors in the field are exposed to adverse operating conditions and are surrounded by dust and dirt. The tiny, thin and sharp broken straw and husks surround the system in reaper operation. The tractors which are equipped with air conditioning system tend to show detrimental effects in cooling performance. The compressor trips frequently by excess pressure developed in the system due to condenser clogging and hence cooling performance is reduced considerably. The air conditioning performance reduces due to the clogged condenser located on the top roof compartment of operator’s cabin, which is better design than keeping in front of radiator where clogging happens every hour and customer need to stop the tractor to clean it with specific blower. The present system is designed keeping condenser at the top of the roof where heavy particles won’t reach easily, So, condenser choking/clogging is observed every 2 hours, this makes the operator to perform repetitive cleaning operations with specific equipment and is a time-consuming process. The present system utilizes the condenser fan operating logic to eliminate this issue and enhance overall system performance by rotating in opposite direction.
Throttles and wastegates are devices used in modern engines for accurate control of the gas flows. It is beneficial, for the control implementation, to have compact and accurate models that describe the flow behavior. The compressible isentropic restriction is a frequently used model, it is simple and reasonable accurate but it has some issues. One special issue is that it predicts that the choking occurs at too high pressure ratios, for example the isentropic model predicts choking at a pressure ratio of 0.52, while experimental data can have choking at 0.4 or even lower. In this work, experimental data is acquired from throttles tested both in a flow bench and mounted as main throttle on a turbocharged gasoline engine. To analyze the flow behavior several flow characterizations are performed at different throttle openings. For the engine installation a special test procedure is adopted and the results show that the engine and the flow bench give the same characteristic behavior of the throttle. In particular, both installations show choking pressure ratios that are significantly lower than what the compressible isentropic restriction predicts. To remedy this and capture the behavior, different modifications of the isentropic model are investigated. Some promising model modifications are analyzed; one that uses the conservation of momentum, energy, and mass to derive a compact expression for the mass flow, and another that uses an ellipse model. All modifications analyzed give lower pressure ratios at choking.
Downsizing has nowadays become the more widespread solution to achieve the quest for reaching the fuel consumption incentive. This size reduction goes with turbocharging in order to keep the engine power constant. To reduce the development costs and to meet the ever tightening regulations, car manufacturers rely more and more on computer simulations. Thus developing accurate and predictable turbocharger models functioning on a wide range of engine life cases became a major requirement in industrial projects. In the current models, compressors and turbines are represented by look-up tables, experimentally measured on a turbocharger test bench, at steady point and high inlet turbine temperature. This method results in limited maps : on the one hand the compressor surge line and on the other hand the flow resistance curve behind the compressor. Mounted on an engine, the turbocharger encounters a wider scale of functioning points. Using only the actual compressor and turbine maps in an engine simulation is sometimes a limiting factor. For this paper a specific experimental campaign has been performed with different automotive turbochargers on a test bench in order to expand the measured iso-speed lines. On the compressor side, new measurements methodologies are described into the choke area, up until a ratio of 0.8, beyond the surge line, into the negative mass flow rate. The results are used to establish semi empirical models of the compressor power in these areas and to study the surge loop amplitude.
Photonic choke-joint (PCJ) structures for dual-polarization waveguides have been investigated at NASA's Goddard Space Flight Center for use in device and component packaging. This interface enables the realization of a high-performance, non-contacting waveguide joint without degrading the in-band signal propagation properties. The choke properties of two tiling approaches — symmetric square Cartesian and octagonal quasi-crystal lattices of metallic posts — are explored and optimal PCJ design parameters are presented. For each of these schemes, the experimental results for structures with finite tilings demonstrate near ideal transmission and reflection performance over a full waveguide band.
Multipath, multistage, erosion-resistant flow control valves have been developed that can sustain the extremely high pressure of deep oil wells. Fitting in the restricted available space and operating using limited power with a long lifetime are challenges for choke valves in the downhole environment of oil wells. These valves must control the flow rate from high-pressure oil reservoirs in the presence of fluids that have non-zero sand concentrations. This design consists of a digitized flow control valve with multipath and multistage pressure reduction structures. Specifically, the valve is configured as a set of parallel flow paths from the inlet to the outlet.
Diesel Engines are known for its low fuel consumption coupled with high specific power output. Downsizing the engines with turbocharging and common rail injection technologies are the recent trends in improving the efficiency and performance of diesel engines. It is very challenging to match the torque targets at low speed and power targets at high speed range of a diesel engines due to system hardware limitation. Torque at lower engine speed will improve a greater extent to the drivability of a vehicle. Formation of black smoke is a major problem in lower engine speeds due lack of air availability. The use of variable geometry, two stage turbocharging and four valves per cylinder are some of the solutions which make the task simpler, also involves additional cost and fundamental design changes. At the same time commonly used waste gate turbocharger for boosting the airflow, fails to deliver required air flow at lower engine speeds. We took the challenge of matching a waste gate turbocharger to the engine torque and power targets. Several iterations have been done at engine test bed to finalize the A/R ratio for turbine followed by the compressor trim optimization to get best low speed torque and high speed power by maintaining the performance limits such as surge, choke margin and turbo speed. This study highlights the thermodynamics involved in matching a turbocharger to an internal combustion engine and standardize the process of turbo matching. Common rail diesel injection technology gives the flexibility in controlling the timing, quantity and number of injections. The injection mass ratio and dwell between the injections of a double-pulse injection strategy have great effect on fuel distributions and air-entrainment inside the sprays. Using the split-injection with small quantity and an appropriate dwell between next injections will play a major role in governing the premixed burn. The subsequent injection of double-pilot injection strategy has a turbulent effect on the fuel-air mixing in diesel sprays. This split injection strategy significantly improve the fuel-air mixing by allowing more air entrain into the spray. Thus, for a direct injection diesel engine, utilizing the turbulent effect of split-injection may enhance the combustion in the later stage and re-burning of the particulate matter in earlier combustion stage, thus reducing the black smoke formation. The in-cylinder pressure and ROHR studies have been performed to better understand the in-cylinder combustion during the split-injection
In cold weather conditions, starting and maintaining low speed stability (engine idle RPM) has been difficult for smaller volume (50cc to 200cc) single cylinder engines. In order to improve the cold start ability without causing any inconvenience to user, automatic choke systems (auto-choke) have been employed. These auto-choke systems enrich the fuel-air mixture depending on predefined operating conditions. For Euro III and Bharat Stage IV (India) emission legislations, cold start emissions are very critical. The objective of this study is to investigate the effect of auto-choke systems on CO, HC, NOx and CO2 emissions in addition to studying temperature and light-off characteristics of catalytic converter of a 4-stroke scooter engine. The vehicle was tested on chassis dynamometer to investigate emissions on WMTC and ECE R40 test driving cycles, with and without the auto-choke system. Three durations of auto-choke operations were studied. The experiment was done with and without after treatment devices (catalytic converter and secondary air injection) to understand the engine out emission characteristics. One of the observations was enrichment of fuel-air mixture due to automatic choke operation results in significant early light-off of the catalytic convertor.
A key technology for further improving the efficiency of gasoline engines lies in downsizing in combination with turbocharging. Decreasing the engine displacement greatly increases the demands on the turbocharging system. The charging of the engine with a single-stage turbocharger leads to a compromise to fulfill the requirements of the nominal power of the engine and the low-end torque. To avoid the use of complex two-stage boosting systems, it is necessary to increase the pressure ratio and the air flow rate at the same time. The wide speed and airflow range of gasoline engines intensify this trade-off. The use of a variable geometry turbine (VGT), additionally equipped with a wastegate bypass, offers great potential to meet the requirements on the turbine side. The range of stable operation of the compressor is limited by choke at high mass flow rates and surge at low mass flow rates. The variable geometry compressor (VGC) is one promising approach to extend the compressor map. A variable charging system consisting of VGC and VGT offers great potential to meet the future requirement for highly boosted engines. The present paper shows experimental investigations of the potential of a variable geometry turbine with an additional wastegate on a small sized gasoline engine. To reach the torque and nominal power characteristic of a 2-stage boosted reference engine, the test engine is additionally equipped with a camshaft phasing system on the exhaust side. In addition two different variable geometry compressors are investigated.
Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off design operation conditions. When used, a most wide operation range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, which permits flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology on a speed-line at near optimal operation condition and near surge operation condition is investigated. A numerical study investigating the flow-field in a centrifugal compressor of an automotive turbocharger has been performed using Large Eddy Simulation. The wheel rotation is handled by the numerically expensive sliding mesh technique. In this analysis, the full compressor geometry (360 deg) is considered. Numerical solutions with and without ported shroud for a near optimal operation condition and near-surge operation condition. The flow-field of the different cases is analyzed to elucidate the functionality of the ported shroud. In agreement with previous observations, it was found that the ported shroud reduces the flow disturbances in the blade passage for all operating conditions. However, the compressor efficiency for the off-design operation condition was found to be higher without the ported shroud, supporting the findings reported recently by an experimental investigation. The computational results are validated with experimental measurements in terms of the performance parameters and available Particle Image Velocimetry data.
High-powered motors typically have very low resistance and inductance (R and L) in their windings. This makes the pulse-width modulated (PWM) control of the current very difficult, especially when the bus voltage (V) is high. These R and L values are dictated by the motor size, torque (Kt), and back-emf (Kb) constants. These constants are in turn set by the voltage and the actuation torque-speed requirements. This problem is often addressed by placing inductive chokes within the controller. This approach is undesirable in that space is taken and heat is added to the controller.
The 912 engine is a well known 4-cylinder horizontally opposed 4-stroke liquid-/air-cooled aircraft engine. The 912 family has a strong track record: 40 000 engines sold / 25 000 still in operation / 5 million flight hours annually. 88% of all light aircraft OEMs use Rotax engines. The 912iS is an evolution of the Rotax 912ULS carbureted engine. The “i” stands for electronic fuel injection which has been developed according to flight standards, providing a better fuel efficiency over the current 912ULS of more than 20% and in a range of 38% to 70% compared to other competitive engines in the light sport, ultra-light aircraft and the general aviation industry. BRP engineers have incorporated several technology enhancements. The fully redundant digital Engine Control Unit (ECU) offers a computer based electronic diagnostic system which makes it easier to diagnose and service the engine. The modern fuel system consists of two fuel rails and two injectors per cylinder, pressure regulator and a return line. Redundant Sensors monitor air box vacuum, exhaust gas temperature, ambient air pressure, inlet air temperature, coolant temperature and throttle position. The injection system ensures optimal fuel and air mixture at any altitude for longer flight range and lower operating costs. This makes the engine more environmentally friendly due to lower CO2 emission levels. Other advantages for the pilots are no manual choke, no carburetor icing, and no requirement for synchronising carburetors. The three-year development period included more than 10,000 hours on the test bench and 700 test hours in the air to ensure 2,000 hours time between overhauls (TBO); the same TBO as the 912 engine. At 63,6kg (140, 2 lbs), the Rotax 912 iS engine delivers the best power-to-weight ratio in its category.
Research on an electrically controlled system which can stably maintain a constant engine speed, while carrying out choke operations using a choke valve when starting the engine, was carried out with the objective of constructing an electrically controlled auto choke system for a general purpose engine that can control both choke mechanism and engine speed with a single motor. Research was also carried out on a mechanism that could drive both the throttle and choke valves with a single motor. First, the throttle valve was fixed in the fully open position and the relationship between the choke valve mechanism and engine speed was analyzed. The relationship between the opening angle of the choke valve and engine speed could be formulated by second order transfer function. However, it became clear that transfer function parameters drastically changed depending on ambient temperature and plug seat temperature. Therefore, instead of using a proportional-integral-derivative (PID) controller, which is stable only under limited conditions, a self-tuning regulator was used to maintain a constant engine speed using a choke valve. By this, a constant engine speed could be controlled with a choke valve regardless of temperature change during operation. A mechanical part for an electrically controlled carburetor to drive both throttle and choke valves with a single motor was designed. This drives the gear, which holds the cam structure, with a single motor. The gear drives the throttle valve, and then drives the choke valve connected to the linkage system by the cam. In this way, the choke valve and throttle valve could be successfully operated without being affected by the other. From these results, an electrically controlled auto choke system for a general purpose engine, which could control both choke mechanism and engine speed with a single motor, was possible.
A set of computer- program routines has been developed for calculating pressure drops and recoveries of flows through standard venturis, nozzle venturis, and orifices. Relative to prior methods used for such calculations, the method implemented by these routines offers greater accuracy because it involves fewer simplifying assumptions and is more generally applicable to wide ranges of flow conditions. These routines are based on conservation of momentum and energy equations for real nonideal fluids, the properties of which are calculated by curve-fitting subroutines based on empirical properties data. These routines are capable of representing cavitating, choked, non-cavitating, and unchoked flow conditions for liquids, gases, and supercritical fluids. For a computation of flow through a given venturi, nozzle venturi, or orifice, the routines determine which flow condition occurs: First, they calculate a throat pressure under the assumption that the flow is unchoked or non-cavitating, then they calculate the throat pressure under the assumption that the flow is choked or cavitating. The assumption that yields the higher throat pressure is selected as the correct one.
Items per page:
50
1 – 50 of 58