نشریه تحقیقات موتور
پیاپی 55 (تابستان 1398)

Driving cycle is one of the important tools to study fuel consumption and emission level of vehicles in urban and intercity. Also, driving cycles are vital for environmental major decision, traffic and road construction managements. On this basis, the present research is to study and analyze the city driving pattern for a car with turbocharged engine in order to extract driving cycle. To this end, the driving cycle was extracted using clustering method from the data measured during real vehicle testing. The results showed that in this driving cycle which lasts almost 1063 sec, the average speed, acceleration, deceleration of this car is 29 km/h, 0.45 and 0.41 m/s2, respectively. Moreover, the car spends 15% of whole driving time in idle stop. The average engine speed is 1337 rpm during the extracted driving cycle. Also, the results showed that among different speed-acceleration ranges, the maximum driving time was belonged to the speed range of 0 to 0.1km/h and the acceleration range of -0.1 to 0.1 m/s2 with the 13.5% contribution of whole driving cycle time. In second and third ranks, 7.5% of driving time is in the speed range of 0.1 to 10 km/h and acceleration range of -1 to -0.1 m/s2, and 7% of driving time spends in the speed range of 30 to 40 km/h and acceleration range of 0.1 to 1 m/s2.

Engine validation tests are important stages of the production development process. Time and cost of these tests have important role in this process. Validation tests investigate performance (function) and durability of engine systems and parts. In recent markets developing of vehicles has accelerated and the validation process should be decreased. Farther more some concepts such as reliability has been serious in this field. Durability tests are longer stages of the validation process and some of them last some weeks. The subject of the accelerated life tests (ALT) is the acceleration of the durability tests without reliability variation. Two manners developed for accelerating durability tests (and decreasing test duration): increasing the severity of loading or removing the cycles that have no (low) influence on failures. In the present research the accessory belt tensioner bracket (feadbracket) tested with the engine supplier procedure for 436 hrs without any failure. In order to accelerating durability test, the belt load increased 1.4 times and bracket was fractured after 200 hrs. After that failure time of the bracket in the usual test extracted via finite element method (FEM) and fatigue models, then the accelerated test time calculated by reliability equations. Results show that ALT duration become less than 200 hrs.

Using an appropriate lubricant is a vital issue for systems like internal combustion engines that they are constantly exposed to friction and wear due to the relative movement of their own components. Since improving properties of engine oil affects the better performance of engine, the addition of nanoparticles is proposed as a solution. Nanoparticles used in this study are Al2O3 which are polar in spite of their excellent characteristics like high thermal conductivity and high wear resistance. In this study, oleic acid is employed as a surface modification agent to prolong the dispersion stability of nanofluid. To examine the effect of nanoparticles size and viscosity of base fluid on dispersion stability of nanofluid, alumina nanoparticles were purchased and surface modified in two particle size of 40-60 nm and 20 nm and they were dispersed in engine oil as base fluid with viscosity of 20w50 and 10w40, both at the same concentration of 0.1wt% as the time passed the samples were photographed and results revealed that nanofluid sample made of 20w50 base fluid and nanoparticles of 40-60 nm exhibited the longest stability of 36 days. The discussed additive powder becomes super fine after surface modification which increases their tendency to agglomerate and precipitate and also the lower viscosity of base fluid which indicates its lower inner friction that will not prevent the precipitation of nanoparticles, are the reasons of lower dispersion stability of other nanfluid samples.

Engine mount bracket is one of the important parts of the car that produced by die-casting method. Failure of engine mount bracket can create irreparable risks. In the operating condition of the vehicle, the engine mount bracket is subjected to oscillatory loading, and manufacturing process such defects caused by uncontrolled casting parameters and its geometrical shape can effect on component fatigue life. In this study, the fatigue life of engine mount bracket was evaluated experimentally. Fatigue strength of specimen is derived that is 1.24 times bigger than critical strength with high dispersion using the Locati-Stair Case method that shows this component in unsafe status. Therefore, finite element simulation was performed to determine the critical areas and improve the geometric shape. The locations of crack initiation were similar in fatigue test and finite element simulation. After improving the geometric shape of engine mount bracket, experimental tests were performed again. The results showed an improvement of fatigue strength up to 1.33 times with lower dispersion that shows component is in safe status.

The homogeneous charge compression ignition (HCCI) engines with ethanol fuel as a renewable fuel is a promising solution to some of the major challenges of combustion engines. Incomplete or misfiring combustion limits HCCI operation and damages the catalyst converter and exhaust systems. The experimental data of a 0.3-liter combustion engine was used for modeling and detecting misfiring combustion. Incomplete and misfiring combustion in HCCI engine was studied by fuzzy-neural network. There is a significant relationship between misfiring combustion and in-cylinder pressure variations at 0, 5, 10, 15 and 20 crankshafts. These experimental findings were used to design a fuzzy-neural network for misfiring incomplete combustion in a HCCI engine. This model has been tested on experimental data. The results showed that the fuzzy-neural network fault diagnostic model can detect incomplete and misfiring combustion in HCCI engine with ethanol fuel. In addition, the developed model was able to identify the transition success from the normal operating area and incomplete combustion.

Delay of oil pressure increasing at the engine starting can effect on wear rate in the internal combustion engine. This paper investigates oil priming behavior of spark ignition engine using two types of gyrator oil pump. So, oil pressure in main gallery and cylinder head is measured with high response oil pressure sensor that synchronized with engine speed in different status of engine starting. Results shows the maximum delay of oil priming is about 2.5 second that is occurred in oil/oil filter changing. Using oil pump No. 2 after 12 hours, can decrease delay of oil priming from 1.93 second to 1.24 second in EF7 engine. Due to using hydraulic tappet technology in this engine, delay of oil priming effect on the engine wear rate and also hydraulic tappet life time. Results show that engine oil pump No. 2 can decrease crank shaft rotation in oil/oil filter changing, cold starting and warm staring status from 58, 45 and 18 revolution to 32, 19 and 11 revolution.