Short communicationFailure analysis of diesel engine piston in transport utility vehicles
Introduction
Engine, since its inception has underwent many technological advances right from external combustion to internal combustion types. Major components of engine include crankshaft, piston, connecting rod, cylinder, cylinder-head etc. Due to functional requirements, these components are given complex shapes which further involves relatively complex manufacturing processes and procedures [12]. Failure of engine components comprised cylinder block breakage, crankpin or crankshaft failure, noise from engine, mixing of oil and water, overheating of engine, blow by and scoring. Each failure possessed one or more causes. Material properties play a significant role in balancing the temperature and force variations that arise due to reasons including but not limited to incomplete fuel combustions, foreign inclusions, burrs, play in joints, manufacturing defects etc. A detailed discussion on materials of different engine components has been presented in succeeding literature review. The synthesis and characterization of nickel (II) complexes were reported by Masoud-Salavati Niasari [8]. Oxidation of cyclohexene using the haacac complexes of Mn(II), Co(II), Ni(II), Cu(II) supported on alumina are investigated, the results of which show that the alumna supported complexes did not undergo color change and can be reused number of times[11]. By thermolysis of Zn surfactant complexes, ZnO nanocrystals were prepared which further are characterized by XRD, SEM, TEM (Transmission Electron Microscopy) HRTEM (High Resolution Transmission Electron Microscopy) energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and ultraviolet–visible (UV–vis) spectroscopy. The synthesized ZnO nanocrystals possess a hexagonal wurtzite structure. Using SEM, the morphology of this structure is inspected and compared with TEM images which reveals that the nanocrystals with diameters ranging from 15 to 25 nm. The diameters of the products are in good agreement with those calculated by XRD patterns [9]. To synthesize zinc sulfide nanoclusters through a reaction between new precursor and thioacetamide, a thioglycolic acid assisted thermal method has been devised. To characterize the achieved findings XRD, TEM, XPS, UV–vis spectroscopy and FT-IR were employed [10]. The air–fuel ratio, type of coolants & oil systems and their interrelationships with the engine functions play a significant role on the performance of piston. For proper engine operation with piston durability & longevity, air–fuel ratio is of prime concern. Piston crown erosion is a consequence of excessive fuel presence or inadequate air [13]. Causes of these include but not limited to clogged air intakes, exhaust restrictions, turbo malfunctions, faulty fuel pump calibrations, contaminations in the fuel injector, fuel injection timing etc. Another attribute for elevated piston temperatures is misalignment of piston cooling spray jets and restricted oil passages. Operating engine at excessive loads i.e. severe lugging or reduced engine revolutions triggers decrease in fresh air volume and results into overheating of piston crown [14]. Elevated engine revolutions i.e. over speeding stretches the component ‘tolerance stack-up’ and due to this, the piston encounters with valve further resulting into shared damage to both piston and valve consequently leading to piston seizure. Building-up of abrasive carbon due to oil circumventing the piston rings because of high base pressure leads to ring scuffing arising from assembly errors.
In present work, failure analysis of various components of engine has been carried out. Analysis methods includes visual inspection of broken parts, water-testing of cylinder block for internal cracks and utilization of advanced techniques of SEM and EDS based on the failure mode and effect analysis. In present work failure data of fifty engines has been collected and analyzed. In present research, piston failed at 302763 km against 400000 km stated by original equipment manufacturer. It is a well-known fact that the engine piston is subjected to elevated temperatures and pressures during combustion and is the source of inertial loads on interconnected parts. Insufficient or no lubrication is one of the main culprits (along with thermal expansion) of piston seizure [2]. Piston failure is faced by all state transport engines and present work is conducted at one of workshops utilized for regular maintenance. The failure data of engine components collected is analyzed using different techniques and remedial actions are devised that further affected the engine performance.
Section snippets
Investigation of engine failures
In present work failure data of 50 failed engines has been collected and analyzed. Occurrence of failure has been observed in various components of engine viz. crankshaft, cooling system, piston, cylinder block, connecting rod, bearings, valves, and camshaft. The failures observed and detected in engine components are enlisted in the table 1.
Further a graph of number of times the failure occurred in respective components of engine is shown in Fig. 1
Failure reasons include but not limited to
Failure mode effect analysis of engine components
Failure mode and effect analysis is a step-by-step process used to identify the potential failure modes. It evaluates processes for failures with serious concerns. In present work FMEA of engine components is conducted by listing individual component failures, failure causes and their effects. The severity of the failures, actual occurrence and detection are also figured out in addition to FMEA [7]. Risk priority number associated with every failure is calculated to prioritize the components
Discussion for failure causes
Referring to above failure mode and effect analysis, the components identified for failures of engine comprise crankshaft, piston, and cylinder block. These three components with RPN greater than 200 are major contributors in engine failure. It is observed that crankshaft fails due to wearing of crankpin bearings. Major reasons of crankshaft failure include misalignment of bearing, overloading of engine & poor/insufficient oil supply leading to wear. Failure of piston is observed through engine
Experimental analysis of failure of engine piston
The experimental analysis of the engine piston is carried using SEM, EDS and XRD techniques. SEM or Scanning Electron Microscopy of the engine piston is carried at magnification levels of 500X, 1000X and 2000X. SEM observations of failed piston head are shown in Fig. 8, Fig. 9 &10. Fig. 8 shows the 500X magnified view of piston head. Consequently Fig. 9, Fig.10 shows the 1000X and 2000X magnified views of failed piston head. Non-uniform surfaces with dislocation of surface material is observed.
Conclusion
Engine and engine components failure data has been collected and analyzed for fifty engines. The number fifty quantifies enough engines to have a substantial insight for understanding the engine failure. Failure in different components of engine and their frequencies during operating situations gives remarkable insight for failure analysis. Further from this data, failure mode and effect analysis has been carried out for all components of engine. Presence of excessive percentage of carbon and
Recommendations to avoid engine failure
The significant cause of engine failure is the failure of cylinder block. However, failure of cylinder block is dependent on the malfunctioning of other associated engine components as piston, camshaft, crankshaft etc. From above analysis, it is observed that percentage of carbon contributes to the scoring of piston, use of worn-out piston rings also lead to piston failure, failure of bearings also leads to imbalance of crankshaft leading to piston failure. Hence it is suggested to avoid
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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