OPERATIONAL ASSESSMENT OF THE EFFECT OF DOB-2E ANTIFRICTION ADDITIVE TO ENGINE OIL ON THE THERMAL REGIME AND FUEL CONSUMPTION OF GAS BUSES

УДК 621.43:621.892

Abstract

Gas buses with engines converted from diesel ones operate in the urban cycle with frequent acceleration, stops and increased heat load, so the properties of engine oil can affect not only wear, but also the consumption of compressed natural gas. The aim of the study was to evaluate the operational effect of the DOB-2E antifriction additive introduced into UNO RED G 15W-40 engine oil at a concentration of 0.5% by weight. The methodology included preliminary laboratory testing of the viscosity, flash point and miscibility of the additive, comparative temperature tests of the oil, as well as operational accounting of gas consumption and temperature parameters on buses with a mileage of more than 200 thousand km. It was found that the use of DOB-2E reduced the maximum oil temperature from 116.6 to 112.6 °C, i.e. by 3.43%. Gas consumption decreased from 25.0 to 24.48-24.70 m3/100 km, which corresponds to savings of 1.2-2.1%. With an annual mileage of 80 thousand km, the estimated savings are 240-420 m3 of gas per bus. The practical significance of the results is to substantiate the possibility of using locally produced boron additives to increase the energy efficiency of gas buses without changing the engine construction.

Аннотация

Работающие на газе автобусы с двигателями, переоборудованными из дизельей, работают в городских условиях с частыми ускорениями, остановками и повышенной тепловой нагрузкой, поэтому свойства моторного масла могут влиять не только на износ, но и на расход сжатого природного газа. Целью исследования является оценка эксплуатационного эффекта антифрикционной присадки DOB-2E, введенной в моторное масло UNO RED G 15W-40 в концентрации 0,5 мас. %. Методика включала предварительную лабораторную проверку вязкости, температуры вспышки и смешиваемости присадок, сравнительные термические испытания образцов масла, а также оперативный учет расхода газа и температурных параметров на автобусах с пробегом более 200 тыс. км. Было обнаружено, что DOB-2E снизил максимальную температуру масла со 116,6 до 112,6 °C, то есть на 3,43 %. Расход газа снизился с 25,0 до 24,48-24,70 м3/100 км, что соответствует экономии топлива на 1,2-2,1 %. При годовом пробеге в 80 тыс. км расчетная экономия составляет 240-420 м3 бензина на автобус. Практическая значимость полученных результатов заключается в обосновании использования местной боро-органической добавки для повышения энергоэффективности автобусов, работающих на газе, без изменения конструкции двигателя.

Keywords: gas-powered bus, gas engine, engine oil, antifriction additive, DOB-2E, temperature control, gas consumption, operational tests.

Ключевые слова: газомоторный автобус, газовый двигатель, моторное масло, антифрикционная присадка, DOB-2E, тепловой режим, расход газа, эксплуатационные испытания.

Introduction

The operation of city buses powered by compressed natural gas is considered as one of the practical ways to reduce fuel costs and reduce the environmental burden of transport. In previous measurements on vehicles running on different types of fuels, it was shown that methane cars have lower average values of CO, CH and CO2 compared to gasoline vehicles, and also do not generate soot emissions typical of the diesel group [1]. However, the environmental advantage of gas fuel does not eliminate the problem of thermal stress of the engine.

Bus engines converted from diesel engines retain the design features of the base engine, but operate under conditions of a different combustion process. In the urban cycle, frequent starts, idling, acceleration with a load and operation at elevated oil temperatures are added to this. Under these conditions, engine oil becomes not only a lubricant, but also a functional element that affects mechanical losses, heat dissipation, and operational stability.

In works on complex additives to crankcase oils, it was noted that antifriction components are able to form a protective film on metal surfaces, reducing direct contact, micro-damage and surface deformation [2]. A study on organoborne additives shows the possibility of converting standard motor oils to an energy-saving class due to locally produced components [3]. Additionally, the results of A. Kuldosheva's work on the organosborane inhibitor confirms that with an increase in the concentration of the protective compound, the corrosion rate decreases, and the degree of protection at 1% reaches 92.12% [4]. These data substantiate the prospects of the boro-organic direction, but do not replace the operational check in the engine.

The working hypothesis of this work is as follows: if the additive DOB-2E is compatible with UNO RED G 15W-40 engine oil and does not cause precipitation, then its introduction at a concentration of 0.5% should reduce the thermal stress of the oil and partially reduce gas consumption by reducing mechanical losses. The aim of the study is to quantify this effect in the operating conditions of urban gas buses.

Materials and methods

The study was carried out according to the sequential verification scheme: laboratory compatibility - temperature behavior of oil - operational inspection on buses. This procedure is necessary because a positive antifriction effect cannot be considered acceptable if the additive impairs viscosity, causes precipitation, or reduces the thermal stability of the oil.

Table 1. Design of a comparative operational experiment

The following indicators were used for the calculation: relative decrease in maximum temperature delta_T = (T0 - T1)/T0 x 100 %, gas savings Delta q = q0 - q1, annual gas savings Ve = Ly/100 x Delta q, where T0 and q0 are values without additives, T1 and q1 are values with additives, L Year - the annual mileage of the bus. This scheme makes it possible to link the laboratory temperature effect with operational fuel economy.

The control group used UNO RED G 15W-40 oil without additives. The experimental group used the same oil with the addition of 0.5% DOB-2E by weight. For comparability, buses with a mileage of more than 200 thousand km running on compressed natural gas in the urban cycle were evaluated. The main controlled parameters were: the maximum oil temperature, the nature of temperature changes in the warm-up and acceleration modes, gas consumption per 100 km and the annual calculated effect.

At the preliminary laboratory stage, it was found that the addition of DOB to class 15W-40 engine oils changes the viscosity and flash point. In the previously obtained data for UNO RED G 15W-40 oil, the introduction of DOB at a concentration of 1% increased the flash point from 195 to 221 °C, while the mixture was classified as fully formed [2]. For long-term use, a lower concentration of 0.5% was adopted, which reduces the risk of excessive viscosity changes and preserves the stability of the oil base.

Results and discussion

Temperature tests have shown that the use of DOB-2E reduces the maximum temperature of UNO oil from 116.6 to 112.6 °C. The absolute decrease is 4.0 °C, the relative decrease is 3.43%. For an operational engine, this indicator is important not in itself, but as an indicator of a decrease in thermal stress in the lubrication system.

Table 2. Key laboratory parameters of oils

At a lower oil temperature, the processes of oxidative aging slow down and the stability of the oil film increases under conditions of boundary friction.

In the operational part, the effect was manifested in a reduction in the consumption of compressed natural gas. The base flow rate is assumed to be 25.0 m3/100 km. After applying 0.5% DOB-2E oil, the flow rate was 24.48-24.70 m3/100 km. The reduction range is 1.2-2.1%. This value is not overestimated for an antifriction mechanism, since the main contribution is expected not from a change in the combustion process, but from a decrease in mechanical losses in the cylinder piston group, bearings and other friction pairs.

Table 3. Temperature behavior of oil

In the operational part, the effect was manifested in a reduction in the consumption of compressed natural gas. The base flow rate is assumed to be 25.0 m3/100 km. After applying 0.5% DOB-2E oil, the flow rate was 24.48-24.70 m3/100 km. The reduction range is 1.2-2.1%. This value is not overestimated for an antifriction mechanism, since the main contribution is expected not from a change in the combustion process, but from a decrease in mechanical losses in the cylinder piston group, bearings and other friction pairs.

With an annual mileage of 80 thousand km, gas savings amount to 240-420 m3 per bus. With a gas price of 5750 soums/m3, the gross savings are 1.38-2.42 million soums/year. Taking into account the additional costs for the additive and preparation of the oil composition, the estimated net effect is 1.24-2.35 million soums/year.

Table 4. Operational and economic impact

The results obtained have applied and scientific significance. The applied value lies in the fact that the effect is achieved without a constructive change in the engine, only by adjusting the composition of the operating material. The scientific significance lies in the confirmation of the relationship between an organoborne antifriction additive, a decrease in the thermal tension of the oil and a decrease in fuel consumption in real conditions of the urban cycle.

However, the results should be interpreted as an operational assessment, and not as the final statistical model for all gas engines. For the doctoral level of further research, it is necessary to expand the sample of buses, record individual mileage, oil temperature for each flight, engine technical condition, compression, oil pressure, and analyze used oil by wear products. This will allow you to calculate confidence intervals, standard deviations, and the statistical significance of differences between groups.

Conclusion

The introduction of 0.5% DOB-2E into UNO RED G 15W-40 engine oil reduces the maximum oil temperature from 116.6 to 112.6 °C, which corresponds to a 3.43% reduction in thermal stress.In operation of gas buses with a mileage of more than 200 thousand km, the consumption of compressed natural gas decreased from 25.0 to 24.48-24.70 m3/100 km, that is, by 1.2-2.1%. With an annual mileage of 80 thousand km, the expected savings are 240-420 m3 of gas per bus, and the estimated net economic effect is 1.24-2.35 million soums per year. The DOB-2E additive can be considered as a promising local component of energy-saving engine oil for gas buses, but its use should be accompanied by a check of miscibility, lack of sediment and viscosity stability.

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