Taşıtlarda yakıt dolum performansını etkileyen parametrelerin incelenmesi

Abstract

Yakıt dolum performansı trafikte faal olarak kullanılan bir taşıtta gerçekleştirilen yakıt dolumunun hem tasarımsal parametreler açısından hem de müşteri memnuniyeti açısından hedeflenen kriterlerin ne kadar karşılandığı olarak açıklanabilir. Yakıt dolum performansında hedef, taşıtın katalog değerinde belirtilmiş olan izin verilen doldurulabilir yakıt miktarından belirli bir tolerans dahilinde dolumun yapılabilmesine ilaveten, müşteriye ya da dolumu gerçekleştirecek operatöre hata modlarını göstermeden ve çevre diğer taşıt sistemlerine olumsuz bir etki bırakmadan gerçekleştirmektir. Özellikle taşıtlarda kullanılan yakıt gibi tutuşması ve alevlenmesi kolay, yangına ya da mal ve can kaybına sebebiyet verebilecek olayların önlenmesi için yakıt ile ilgili her konuda gerektiği gibi yakıt dolumunda da prosesin de yakından incelenmesi gerekir. Bu inceleme ile birlikte hem olası hata modlarının neler olabileceği, bu hata modlarının hangi kök nedenlerden kaynaklanabileceği, ortaya çıkan hata modlarının nasıl önlenebileceğinin yanı sıra yakıt dolum performansına etki eden hem çevresel hem de tasarımsal parametreler ile bu parametrelerin etkileri incelenmiştir. İnceleme toplamda 8 ana bölümden oluşmaktadır. Birinci bölümde yakıt dolumunun nasıl gerçekleştirildiği ve yakıt dolum performansı ile ne anlatılmak istendiği açıklanmıştır. Ayrıca bu bölümde yakıt dolumuna etki eden regülasyonlardan da bahsedilmiştir. İkinci bölümde ise yakıt dolumunda görev alan tüm alt sistemler ve komponentleri tanıtılmıştır. Üçüncü bölümde ise yakıt dolum performansında istenilen seviye ve bu seviyenin karşılanamaması durumunda oluşabilecek hata modları tanıtılmıştır. Dördüncü bölüm dahilinde yakıt dolum performansına etki edebilecek ya da etmesi beklenen parametrelerin ne olduğuna bakılmıştır. Yakıt dolumu için önemli parametrelerden birisi olan ve hem yakıt dolumunu gerçekleştiren kişiden hem de taşıt üreticisi firmaların tasarım departmanlarından bağımsız en büyük parametrelerden birisi olan tabanca türlerinin detayları verilmiştir. Beşinci bölümde yakıt dolum performansı testlerinin gerçekleştirilmesi sırasında kullanılacak ekipmanlar, incelenecek çıktılar, testin nasıl gerçekleştirileceği ve teste girecek olan taşıtlar ile test planları bulunmaktadır. Altıncı bölümde test sonucunda elde edilen verilere göre belirlenen parametrelerin yakıt dolum performansına nasıl etki ettikleri gösterilmiştir. Bu bölümde bölümde ayrıca etkisi olması beklendiği halde etkisi olmayan parametreler de belirlenmiştir. Yedinci bölümde elde edilen bulgular ışığında optimum yakıt dolum performansı için dikkat edilmesi gereken noktalar ve optimum yakıt sistemi tasarımı için tavsiyeler bulunmanktadır. Son bölüm olan sekizinci bölümde ise teste giren taşıtların mukayesesine ek olarak incelemenin taşıt üreticisi firmalar açısından faydası ve bu incelemenin ileride nasıl geliştirilebileceğine dair fikirler paylaşılmıştır.

Refueling performance can be stated as how much the demanded acceptance criteria are met according to design and customer satisfaction during a refueling process on an active road vehicle. Target of a successful refueling process is to fill up the fuel tank up to given catalogue value within its tolerances while showing no failure modes to customer or operator and no negative effect to surrounding other vehicle systems. Like the other fuel related processes refueling process must be also examined closely as road vehicle fuel types are flammable or easy to ignite and that can lead to fires causing loss of life and property. With this examination it will be possible to determine possible failure modes, these failure modes' root causes, how these failure modes can be avoided along what are design related and environmental parameters affecting refueling and how they are affecting. This investigation consists 8 main chapters. In the first chapter refueling process and refueling performance are explained in details. Additionally emission regulations are mentioned in this chapter. Fuel sub-systems and fuel components are introduced in second chapter. In third chapter demanded refueling performance is explained and failure modes are defined. Parameters that can or may have an effect on refueling are determined in fourth chapter. One of the main parameters that can have an effect on refueling independent from vehicle manufacturers and customers/operators is nozzle type and many nozzle types are introduced in this chapter. In fifth chapter equipment that will be used during refueling performance test, output that will be examined, test procedure and vehicles to be tested along test plans are given. In sixth chapter it is investigated that which parameter affects refueling performance and how it affects. Also parameters that are expected to have an effect on refueling but not are classified. In seventh chapter important points for refueling performance is stated in the light of outcomes of refueling performance tests with advices for an optimum fuel system design. In the last and eighth chapter comparison of test vehicles, benefits of this investigation to vehicle manufacturers and how this investigation can be developed in future stages are given. Refueling process can be considered as a simple fuel flow from fuel dispenser to fuel tank shell of fuel system of the vehicle. In theory this is basically true but a very very short summary of the phenomena. In refueling many physical event takes place and it is a combination of high degree fluid mechanics both related with liquid state and gaseous state. In refueling it is very important to consider both liquid pressure drop and vapor management. Refillable volume, dispensed fuel and nozzle shut-off are determined by system pressure build-up. A good refueling performance is achieving a full fuel tank shell based on catalogue values given by vehicle manufacturers along with no error states or failure modes like, spitback, wellback, premature shut-off, not being able to start refueling, violation of emission regulations that vehicle will be sold, damage or harm to surrounding vehicle systems or inflammation and ignition inside the fuel system. Fuel system's refueling related side is composed of three main subsystems which are fuel filling subsystem, fuel tank subsystem and evaporative emissions subsystem. In fuel filling subsystem there may be up to six component groups that are fuel filler pipe, fuel filler insert, fuel filler neck and head, fuel hoses, clamps and flow regulator parts. Under fuel tank subsystem there may be up to four component groups that are fuel tank shell, in-tank valves, fuel tank straps with fasteners and fuel distribution modules. Under evaporative emission subsystem there may be up to three component groups that are vapor lines, atmospheric line and carbon canister. For a good or optimum refueling performance fuel system designers are aiming to fill the fuel tank shell just around exact allowed fillable level. If fillable level will not be met but will stay in limits a little higher filling volume is appreciated. All other targets given above are almost mandatory and it is strongly recommended to be met. If required refueling performance cannot be met there must be a reason and as a result there should be a failure mode related with the issue. In result of a bad refueling performance the person performing the refueling process may face with spitback which is a slight amount of fuel coming out of fuel system after shut off, wellback which is a state that even the fuel system is filled but nozzle does not shut off, premature shut off where nozzle shuts off but fuel system is not filled until its allowed fillable capacity, not being able to start refueling, violation of emission regulations that vehicle will be sold which is a exceed of limits allowed by regulations or laws that are applicable for mentioned vehicle, damage or harm to surrounding vehicle systems such as damage to body paint or fuel spillage on exhaust system and inflammation and ignition inside the fuel system due to high friction between fuel system and fuel, especially on gasoline fueled vehicles. Parameters that may have an effect on refueling can be classified in six main groups. First group is environmental parameters such as ambient temperature, ambient pressure or transportation conditions. Another group is customer or operator based parameters such as positioning of vehicle in fuel stations that may lead to improper latching or different clock position orientation then 6 o'clock position. Also leaning on nozzle is a parameter for this group. In third group it is possible to combine time based parameters such as metal fatigue, creep or torque loss of fastener that can lead to malfunctions on fuel systems. In fourth group there is the relation with surrounding components such as excessive heat transfer from exhaust system or bad tolerance stack up on body system components that may change the position of fuel system parts. Fifth group is the refueling equipment related parameters such as nozzle types and flow rates. Last group is the design related parameters such as inlet angle, height of inlet point from ground or routing of fuel filler pipe. As having a complete vehicle for testing is expensive and it is way hard to dispense fuel after refueling fixtures are built for refueling performance tests. Having a fixture will also allow having the instrumentation easier compared to having vehicle. Only important point is to build the fixture as matching as with the original position of vehicle. Fixture should be built vehicle's most selling variant for each fuel type. After fixture build test fuels to be determined for refueling tests. Test fuels must be chosen according to markets that vehicles will be sold. This process must be repeated for nozzle types also. After completing instrumentation and choosing the data channels to be tracked test procedure is determined. Every vehicle manufacturer company has their own standards built on their own experience and know-how. After completing the all selection above last action is to determine the vehicle or vehicles for refueling performance test. Key factor in determining the test vehicles is to allow a healthy comparison and a good examination base for all parameters. This leads to vehicles some same and some different properties within each other. In final test plan can be built to see how many refueling will be performed on which vehicle with which fuel type and with which different parameters. Investigation starts after completing all refueling tests. Test results are datamined for determining the parameter or parameters that has no significant or useful effect on refueling performance. Later on effect of fuel flow rate, nozzle type rate, positioning and orientation of nozzle, type of fuel filler insert, all design related parameters, type of fuel used in refueling performance tests, dispensed fuel temperature and ambient temperature are defined. All those parameters have different effects and any major change of these parameters cause or eliminate different failure modes in every vehicle. In the light of all test results and after defining all parameters effects of refueling process it can be proposed how the fuel system and components' design should be for an optimum refueling performance. It may not be possible to find a common fuel system design for all vehicle's all variants but defining refueling performance affecting parameters can give an idea for the design. All three vehicles in this investigation are compared to each other for a final conclusion and understanding. Benefits of this investigation can lead to the refueling performance such as reduction is warranty costs and increase in customer satisfaction which will also result in positive for vehicle manufacturer's economics.