Pumpability — Past Accomplishments; Present and Future Challenges

Abstract

The possible problem of inadequate low-temperature engine oil pumpability was considered in the early '60s and grew into prominence in the late '60s and early '70s with the success of the automotive industry in improving low-temperature engine startability. Reported incidents of field pumpability problems in the early '70s led to an extensive ASTM study using several cold-rooms and a number of reference oils. This study confirmed the previously anticipated existence of two forms of pumpability problems — flow-limited pumpability caused by higher viscosities and air-binding pumpability caused by engine oil gelation under certain cooling conditions. Of these two forms of engine pumpability failure, air-binding was the primary threat to engine life. This was a consequence of the fact that some engine oil formulations could be induced to gelate at temperatures well above viscosity-limited temperatures. Despite these extensive cold-room studies and the development of a Mini-Rotary Viscometer bench test closely simulating the cold-room results, the work did not prepare those studying the problem area for the disastrous winter of 1980–81 when several million dollars of engines failed in the field as a result of air-binding oil effects. In renewed efforts to develop viable bench tests correlating to these field-failing engine oils representing real world conditions, two instruments emerged: one in 1982 called the Scanning Brookfield Technique and the second, a further adaptation of the original MiniRotary Viscometer (called the MRV TP-1), in 1985. Another recent ASTM cold-room study has confirmed improved startability and brought into question whether or not modern engines are less prone to air-binding. At the same time, new pressures on both automotive and heavy-duty diesel engines have just come to attention as a consequence of long drain intervals and their effects on engine oil oxidation. It has been shown that such intervals can have serious effects on the engine through the coupling of both viscosity-limited and air-binding characteristics, In a similar manner, high soot loading in diesel engines recently redesigned to reduce oxides of nitrogen has produced further low-temperature pumpability problems and the associated needs to understand the chemistry and rheology of such oils at these temperatures and to find ways of reliably and repeatably measuring these phenomena.

Theoretical approach to a better understanding of gelation in the framework of petroleum industry: role played by different parameters

“…Concretely, the Mini Rotary reports viscosities lower than the SBT in absence of yield stress and larger for measured values of yield stress. The first behaviour mentioned above has been reported in the literature [23] and it has been attributed to the effect of the shearing on the rheology of the oil [20]. On the other hand, it is evident that the continuous shearing of the oil carried out in the scanning slows down the formation of the volumespanning crystal network which entrains the remaining liquid oil among the crystals.…”

“…(8)) is plotted as a function of the temperature. Figure 1 shows the main features of the gelation curve for a gelating oil [23]. This system behaves like a perfect Newtonian oil in a wide interval of temperatures in which G takes a constant value (zone I).…”

Thermal History of the Engine Oil and Its Effects on Low-Temperature Pumpability and Gelation Formation

“…It was reasoned that by gently causing oil molecules to slide past one another in laminar flow, those oil molecules capable of producing gelation would be physically moved into a proximity with one another that might not have otherwise occurred with Brownian motion -particularly at lower temperatures and relatively high viscosities where the natural motion of these larger molecules is considerably retarded. [11]. THE SCANNING BROOKFIELD TECHNIQUE -There are several important steps in the Scanning Brookfield Technique.…”