SNPI Tuning
Autronic Gas Tuner
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Autronic Gas Tunner
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« เมื่อ: กันยายน 09, 2008, 09:19:30 AM » |
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GAS INJECTION SYSTEMS FOR MOTOR VEHICLES When under attack of scientific-technical progress the carburetion systems of fuel feeding, which dominated in the automotive industry for a long time, have surrendered to the injection systems, the best days of the traditional reducer gas systems were left in the past.
Shortly before the dawning of the new age of automotive industry, the gas equipment manufacturers started active research of solutions for adaptation of traditional reducer gas systems to the reality of the modern injection motor vehicle. The systems were complicated by the introduction of new electronic devices, and every new combination was declared by the proud name of the ‘new generation’. However the result still remained unsatisfactory, as long as, similarly to the reducer systems, the gas feeding as before was realized through the mixer in the space in front of the choker, far from the combustion chamber. Serious disadvantages of this fuel feeding strategy become apparent in unstable operation of the engine, danger of inflaming of the gas-air mixture which fills up the inlet manifold, and destruction of the inlet manifold itself (so called ‘backfire’), significant deterioration of dynamic properties of the motor vehicle and excessively high gas consumption. Finally, after a series of unsuccessful experiments, the understanding came that for realization of a possibility of injection motor vehicle operation on gas fuel, the modern gas system must have in its principles the algorithms of operation similar to ones of the modern petrol system, as well as the gas reducer repeated the logic of operation of the petrol carburettor. In that system the fuel feeding must be not constant, but cyclic, and the position of the gas feeding device must be as close as possible to the combustion chamber. Therefore the commonly used system of classification of automotive gas systems generations, if it is considered from the principle of fuel dosing, seems somewhat artificial with improper assignment of new generation statuses. The distributed gas injection is the principally new technology, which is in fact the true second generation of automotive gas systems. In any case the numeration of generations is the matter of preferences; meanwhile the real operational properties of systems of different manufacturers and the differences in their constructions are of indubitable interest.
DESCRIPTION OF THE DISTRIBUTED GAS INJECTION SYSTEM AND ITS MOST IMPORTANT FEATURES COMMON PRINCIPLE OF OPERATION The liquefied petroleum gas (LPG) contained in the tank is fed under its own pressure through the copper tubes into the under-bonnet space of the car. The usual pressure of LPG in the tank is 7-12 Bar in summer, and 0.5 - 4 Bar in winter. When the temperature arrives to -43°C the pressure falls down to zero and the feeding of LPG stops. The LPG passes through the solenoid cut-off valve and enters into the reducer. The refrigeration liquid of the engine is led to the reducer for heating, thus causing active vaporization of LPG. During vaporization the LPG expands and creates the operational pressure. The value of the operational pressure can be adjusted by the manufacturer, or the possibility of adjustment is provided on the reducer. Usually the adjustment is realized by the rotation of the screw placed in the centre of the front cover of the reducer. Then the evaporated gas passes through the hose to the fine filter, where the mechanical admixtures are separated. After the filter gas passes through the hoses in the distribution rail, from which it passes to gas injectors. The gas injector opens by the signal of electronic control unit (ECU), letting the gas dose pass, and closes upon the end of the ECU signal. The petrol feeding scheme repeats with the only peculiarity, that gas, in contrast to petrol, mixes very well with air, and doesn’t need a carefully formed dispersing jet.
The ECU reads control signals of petrol injectors from the original ECU of the motor vehicle, as well as signals of additional sensors supplied with the gas system, and creates by the calculation method the control signals of gas injectors, switching off the petrol injectors at the same time.
REDUCER Gas fuel as before comes from the tank to the reducer fixed in the under-bonnet space of the car. The reducer evaporates the liquid phase of LPG and stabilizes the output pressure in the range from 0,2 to 1 Bar. In the gas injection systems the reducer has no dosing function, it has no thin, sensible diaphragms. For that reason the injection reducer is much more reliable than reducers of the past generation systems. From the construction point of view it reminds the reducer of the gas-stove, with the vaporizer added. At the same time regardless all simplicity of its construction the injection reducer must maintain effectively the given pressure and temperature of the evaporated gas. If the pressure or the temperature on the injection reducer becomes unstable, the electronics will be not able to compensate completely the arising dosing errors. To provide the stable temperature of gas going out of the reducer it is necessary to let it flow as long as possible through the internal channels of the reducer, to whirl and to absorb heat from the warm walls. So the key parameters of the reducer are the developed internal contact surfaces and its size: the bigger, the better.
FINE GAS FILTER The demands to this component are very simple - to maintain the containment at the maximum allowable pressure and to pass a sufficient quantity of the filtered gas. The filtering purity is up to 5-7 micrometers. Even if it is very similar to filters for petrol injectors, they are not interchangeable. The petrol filter has the porosity in the range of 12-17 micrometers, and in case of application in the gas injection doesn’t guarantee necessary purification efficiency. It can cause damage of the most crucial component of the whole system, the gas injector.
GAS INJECTOR
The gas injector is the most crucial component of the whole system. The quality of operation of the motor vehicle on gas depends mainly on the characteristics of the gas injector.
The gas injector: - must maintain the external containment at the maximum allowable pressure; - leakage through the working pair seat-core must not exceed the limit allowable by the standard in the course of all period of the product exploitation; - as the speed of response must be close to the petrol injector, that is the opening time must not exceed 2,0-2,5 ms, or better to be less than 2,0 ms; - dosing characteristics of all injectors on one motor vehicle must be equal, and the mistake must be within 10%; - characteristics must securely remain invariable on the mileage of 50-80 thousands kilometres, and the common life length must approach to the lifetime of the car; - electric power consumption must be as small as possible, but sufficient to provide the origin of necessary magnetic force
In the gas system FAVORIT we have tried to develop the gas injector corresponding to the highest requirements of exploitation, which is capable to maintain operability in the most rigid conditions, with a sufficiently low cost of the product itself.
Solution of the life length task If we convert approximately kilometres of mileage into the quantity of operational cycles, for the sequential (separate injection in every cylinder) type of injection, every 1000 km correspond to about 1.000.000 operational cycles, for the semi-full group type of injection (pair of injectors operate simultaneously) to about 2.000.000 operational cycles. On the mileage of 50000 km every injector shall response from 50 to 100 million times respectively. Such a life length can be achieved if the durable wear-resistant materials are used, from which the most correct way could be implementation of hard alloys or surface hardened compositions. In our case we have selected the second way. Many manufacturers in their injector have used the brass seat, and in the core have inserted the rubber gasket, in order to provide the containment of closing. With this solution they avoided some problems. For example, so called “condensate” in the injector attempts to stick the core to the seat, so the engine begins to work unstably with falling-out of one or several cylinders (“misfire”), but if the core has the rubber gasket, it sticks off very easily, in comparison with the fully steel core-seat pair. To imagine the difference try to put rubber plate on wet glass. Taking the rubber for one edge, it is easy to separate surfaces one from another. Otherwise if to put on the wet glass another glass, it will be very difficult to separate the surfaces. Quite the same thing happens in the gas injector one million times every thousand kilometres. It is easier for the injector with rubber gasket, but it wears quickly. For the steel injector it is more complicated, but it is durable. We have selected the straight way: measured the exertion needed to overcome the condensate sticking, and created in the injector the magnetic circuit, which overcomes securely this additional exertion. Anyway it is needless to count on that the fuel will be pure.
Solution of task of injector opening speed The majority of gas injectors available on the global market have the opening time more than 3.0-3.5 ms. But that means that if the car has a semi-full group injection, and the injection time on idling is 1.3-2.0 ms, to provide the physics capacity to work of such an injector, it is necessary to increase the injection time to 3.5 ms, and reduce respectively an open flow area of the injector and the gas feeding pressure. With this kind of tuning it will be very difficult to provide a necessary gas flow at the maximum load mode, otherwise it will be necessary to switch to petrol, and than back to gas. There is another option, when at the insufficient gas flow the petrol is added simultaneously with gas. The driver will hardly note it, but the calculated gas consumption will be improbably low. In the most cases the manufacturers of gas equipment pass over in silence this peculiarity of no small importance.
About the gas consumption If we open the Bosch Automotive handbook, we can read with much interest, that for execution of the same work the necessary quantity of LPG is on 28% higher than the quantity of petrol. So, every diminution of LPG consumption doesn’t pass without leaving a trace. Or we have lost the dynamics of acceleration, or we have worsened the exhaust emission, and by that have complicated the operation of the catalyst converter, risking in case of its breakdown to meet serious financial consequences. Slavgas has chosen another way. We have set us a task to provide such a response speed and performance characteristic of the injector, at which for the same work done by the engine the length of gas injection will be as close as possible to the length of petrol injection. So we provide the adequate gas flow through the injector within the whole range of loads. The opening time of out injector is from 1.5 to 2.0 ms according to the model.
Stability of injector’s characteristics For smooth and stable operation of the engine the difference in the productivity between all injectors on one car must not exceed 7-10%. The operability of injector depends on many factors, which cannot always be foreseen in advance. For example, some refuse can fall into the injector, like a piece of rubber of the connecting hose. If it is difficult to apply on-the-fly to a workshop for repair, or replace the injector with the new one, the possibility to recover the operability of the injector in the field conditions, with the full recovery of initial characteristics of injector and the whole gas system, presents itself as an important advantage.
The gas injector FAVORIT has one of rare constructions, which is repairable without influence on characteristics of the injector. For that it is sufficient to screw out the output nozzle of the injector, to wipe and to blow out the internal parts of the injector, set them back, screw tight the nozzle till the mark on the body. The operability and initial characteristics of the injector will be restored. The majority of existing gas injectors or cannot be disassembled, or after dismantling need to be adjusted on a special stand, or need a special additional equipment for cleaning.
INJECTION RAIL Actually there are two mostly common concepts of gas injectors mounting on the car: - injectors united in a common injection rail
- separate injectors
In both cases there are their advantages and disadvantages. At the mounting of gas injectors it is necessary to provide the same distance from the injector to the inlet valve on different cylinders, in order to achieve the uniform gas feeding and therefore the smooth engine operation. On the other hand, is necessary that the distance itself from the injector to the engine cylinder was possibly minimal. In case of injection rail the length of rubber hose from every single injector in the rail it is necessary to equalize to the longest hose, because the position of inlet manifolds of the engine is always wider than the injection rail itself. The higher is the distance from the rail to the combustion chamber, the less precise is the gas dosing in the most critical, transitional modes of operation, like acceleration, evolution, in word every manoeuvre related with sharp change of load on the engine. However the injection rail has its advantages as well. The execution of the one body for several injectors is always cheaper than a single body for every injector. One more advantage is that during the mounting of the injection rail one needs less connections of gas hoses, because there is no connection from the rail to injectors. By the way the constructive realization of injectors has a noticeable influence on the temperature of gas. The common rail with massive, more often aluminium body, and with coils mounted over it, chills gas so that the rail covers with hoar-frost on high loads. On the other hand the single injector, where the body serves contemporaneously as a magnetic circuit, the gas is heated also by the solenoid coil, releasing it in turn from excessive temperature tension. As obvious disadvantages of the single injector construction can be noted the higher price due to the manufacturing of a separate body for every injector, and the higher quantity of gas hose connections from the rail to the injectors. However from the point of view of quality of mounting, serviceability and engine operation quality this construction has irrefutable advantages over the injection rail: - single injectors can easier be placed on the engine in the limited space conditions; - the distance from the injector to the inlet cylinder is minimal; - the distance from rail to the injector doesn’t influence on characteristics of the system; - in case of necessary maintenance it is possible to dismantle only one injector, not the whole injection rail; - it is possible to replace only one injector, which is excluded in case of injection rail. When we started to project the gas injector, we have taken into consideration as all particular qualities mentioned above as many other features, which seriously influence on operability of the system. As a result we have put into serial production a family of injectors, which correspond to the most rigid environment demands. The injector FAVORIT is able to work as a part of any gas injection system with any ECU, in all climatic conditions, on any injection motor vehicle.
ELECTRONIC CONTROL UNIT is also one of the key components of the gas injection system. Actually there is no common opinion which logic of interaction between ECU of the car and ECU of the gas system is optimal. There are fully independent programs of gas injection control, combined programs, fully dependent on the regular ECU of the car. Everyone has its pluses and minuses. Hereby we mark some common characteristics of ECUs and wiring harnesses, to which it is worth to focus attention on: - complexity of mounting of the ECU on the car. It influences on time, work content, and therefore the work cost, and on the possibility of mounting errors. - quantity and types of sensors used in the system. As a rule, the reliable and correct operation of the system depends on the reliability of sensors, which is one of sensitive points of gas equipment. Without sensors it is impossible to execute some useful functions, like automatic switching from one fuel type to another, correction of fuel feeding according to some external and internal factors, automatic adjustment of the gas system. The customer must have the possibility to select the system with both more complicated and expensive ECU and simpler and cheaper ECU. Slavgas offers these options in the range of its production. - stability of the ECU against various noise during the engine operation; - secure electric compatibility with other on-board electronic devices of the car. These demands must be fulfilled during the certification tests of the equipment.
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