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Dive into the research topics where Rehan Zahid is active.

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Featured researches published by Rehan Zahid.


Journal of Nanoparticle Research | 2016

Tribological performance of nanoparticles as lubricating oil additives

Mubashir Gulzar; H.H. Masjuki; M.A. Kalam; M. Varman; N.W.M. Zulkifli; Riaz A. Mufti; Rehan Zahid

The prospect of modern tribology has been expanded with the advent of nanomaterial-based lubrication systems, whose development was facilitated by the nanotechnology in recent years. In literature, a variety of nanoparticles have been used as lubricant additives with potentially interesting friction and wear properties. To date, although there has been a great deal of experimental research on nanoparticles as lubricating oil additives, many aspects of their tribological behavior are yet to be fully understood. With growing number of possibilities, the key question is: what types of nanoparticles act as a better lubricating oil additive and why? To answer this question, this paper reviews main types of nanoparticles that have been used as lubricants additives and outlines the mechanisms by which they are currently believed to function. Significant aspects of their tribological behavior such as dispersion stability and morphology are also highlighted.


Tribology Letters | 2015

Effect of Lubricant Formulations on the Tribological Performance of Self-Mated Doped DLC Contacts: a review

Rehan Zahid; H.H. Masjuki; M. Varman; Riaz A. Mufti; M.A. Kalam; Mubashir Gulzar

AbstractnDiamond-like carbon (DLC) coatings have emerged as one of the most promising surface coatings for applications involving boundary lubrication regime. Some of the characteristics that distinguish DLC coatings from other hard coatings include high hardness, low friction coefficient, wear resistance, and chemical inertness. Because of their low surface energies, these coatings cannot react effectively with different lubricant constituents. Doping of DLC coatings with metals and nonmetals, such as titanium, tungsten, silicon, chromium, fluorine, and nitrogen, can improve their interaction with lubricants to form tribologically beneficial films. Many experimental studies have been conducted on different types of DLC coatings using various lubricant formulations in the last few decades. The results obtained from these experimental studies are very scattered and contradictory, so the data should be consolidated in a more organized and apprehensible manner. By doing so, tribological behavior of various DLC–lubricant combinations can be understood in a better way, and a more logical continuation of research on DLC coatings can be carried out. In this review paper, most widely investigated metal- and nonmetal-doped DLC coatings, such as Ti-DLC, W-DLC, Si-DLC, Cr-DLC, WC-DLC, and multilayered a-C:H/W-DLC coatings, are considered for evaluation. Tribological performance of the aforementioned DLC coatings, in combination with various base oils and lubricant additives, is analyzed by comparing their average friction and wear coefficient values, which have been calculated from published experimental data. Only self-mated doped DLC contacts are considered in this study to eradicate the interference of ferrous and nonferrous counterbodies.


Tribology Transactions | 2017

Dispersion Stability and Tribological Characteristics of TiO2/SiO2 Nanocomposite-Enriched Biobased Lubricant

Mubashir Gulzar; H.H. Masjuki; M.A. Kalam; M. Varman; N.W.M. Zulkifli; Riaz A. Mufti; Rehan Zahid; Robiah Yunus

ABSTRACT The stable dispersion of nano-additives is highly desirable for the effective lubrication performance of nanolubricants. The compatibility of base oil with selected nano-additives is required for uniform and stable dispersion. This research evaluated the dispersion stability and tribological characteristics of nano-TiO2/SiO2 (average particle size 50 nm) as an additive in a biobased lubricant. The wear protection and friction reducing characteristics of the formulations were evaluated by four-ball extreme pressure tests and piston ring–cylinder liner sliding tests. Surface analysis tools, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy, were used to characterize the worn surfaces. Results showed that the nanolubricants demonstrated appreciable dispersion capability in the absence of a surfactant and an improvement in load-carrying capacity, antiwear behavior, and friction reduction capability.


Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | 2015

Experimental measurement of roller slip in end-pivoted roller follower valve train

Muhammad Khurram; Riaz A. Mufti; Rehan Zahid; Naqash Afzal; Usman Bhutta

Direct-acting tappets and end-pivoted roller followers are the two main types of valve train configurations widely used in passenger car engines. Considerable theoretical and experimental work has been carried out on the direct-acting valve train. However, due to complex nature of the end-pivoted rollers, limited work has been carried out in this area. In roller follower valve train, the roller rotation has a direct impact on the performance in terms of component durability and friction. Roller rotation minimizes the chances of fatigue failure by even distribution of wear, improves the lubrication, and influences the valve train power loss. In this research work, the effect of lubricant rheology and operating conditions on the performance of end-pivoted roller follower has been studied experimentally in detail. Tests have been carried out on real production engine, avoiding any major modification to the components under investigation. The tests revealed presence of roller slip at certain operating conditions. Lubricant viscosity played a key role in the slippage of roller at lower temperatures, however, at high temperatures, negative slip was observed indicating that component inertia has a role to play in roller slip. High camshaft operating speeds and roller inertia increased the tendency of slippage. The study of roller slip was not possible without the development of a new method of measuring roller performance, also reported in this paper. The experimental set up, roller rotation measurement system, test procedure, and results are presented and discussed in detail.


Critical Reviews in Solid State and Materials Sciences | 2017

A Review on Effects of Lubricant Formulations on Tribological Performance and Boundary Lubrication Mechanisms of Non-Doped DLC/DLC Contacts

Rehan Zahid; Masjuki Haji Hassan; M. Varman; Riaz A. Mufti; M.A. Kalam; N.W.M. Zulkifli; Mubashir Gulzar

ABSTRACT Tribological efficiency of industrial applications involving boundary lubrication regime can be improved to an appreciable extent by the deposition of hard coatings on interacting surfaces. Among such coatings, diamond-like carbon (DLC) coatings are considered to be one of the most suitable ones for the said role. DLC coatings possess a unique combination of physical, chemical, and material properties due to which they can help in minimizing friction-induced energy and material losses even under starved lubrication conditions. Since commercial lubricants are optimized for steel surfaces, therefore, a lot of experimental investigations were carried out to analyze the tribological compatibility of these lubricants with various DLC coatings. However, there is still a lack of understanding about how DLC coatings interact with conventional lubricant additives. Some researchers reported tribologically beneficial interactions between DLC coatings and formulated lubricants while others observed no such behavior. To address these inconsistencies, there is a need to rearrange the published data in a more apprehensible and organized manner with a special emphasis on the mechanisms responsible for a particular tribological behavior. In this way, it can be determined whether synergistic or antagonistic correlation exists between a particular DLC-lubricant combination and research on DLC coatings can be continued in a logical way. In this article, most widely investigated non-doped DLC coatings (ta-C, a-C:H, a-C, and ta-C:H) are tribologically analyzed. Average values of friction and wear coefficients are calculated for various DLC-lubricant combinations using already published data and compared to quantify the effectiveness of a particular lubricant additive in enhancing tribological characteristics of symmetrical non-doped DLC contacts. Moreover, tribological performance parameters of non-doped DLC coatings are compared with those of doped-DLC coatings to understand differences in their tribological behavior in combination with additives.


RSC Advances | 2017

Investigation of the tribochemical interactions of a tungsten-doped diamond-like carbon coating (W-DLC) with formulated palm trimethylolpropane ester (TMP) and polyalphaolefin (PAO)

Rehan Zahid; Masjuki Haji Hassan; Abdullah Alabdulkarem; M. Varman; Riaz A. Mufti; M.A. Kalam; N.W.M. Zulkifli; Mubashir Gulzar; Tom Lee

Modern day industrial applications involve rigorous operating conditions, which include high temperature, heavy applied loads, and starved lubrication conditions. In these scenarios, either the lubricant slips out of the contact or only a thin layer of lubricant resides between interacting surfaces. The deposition of diamond-like carbon (DLC) coatings possessing extreme wear resistance and ultra-low friction characteristics and using lubricants capable of physically adsorbing on the interacting surfaces can significantly improve the tribological performance. Due to their superior tribological characteristics, chemically modified vegetable oils, such as palm trimethylolpropane ester (TMP), are one of the potential candidates to be used as lubricant base-oils. To prove the suitability of TMP and DLC coatings for applications involving a boundary-lubrication regime, a logical step forward is to investigate their tribological characteristics in combination with conventional lubricant additives. In this study, the extreme pressure characteristics of TMP formulated with glycerol monooleate (GMO), molybdenum dithiocarbamate (MoDTC), and zinc dialkyldithiophosphate (ZDDP) in combination with steel/steel contact were investigated using a four-ball wear tester. In addition, the tribochemical compatibility of the abovementioned additives with TMP and a tungsten-doped diamond-like carbon coating (W-DLC) was also analyzed using a universal wear testing machine. For comparison, additive-free and formulated versions of polyalphaolefin (PAO) were used as a reference. Moreover, various surface characterization techniques were used to investigate the mechanisms responsible for a particular tribological behavior. TMP-based lubricants exhibited superior extreme pressure characteristics and friction performance as compared to those containing PAO. An improvement in the tribological performance was observed when W-DLC-coated surfaces were used instead of uncoated-surfaces irrespective of the lubricant formulation.


international conference on wireless communications and mobile computing | 2014

On the performance of multiple region reverse frequency allocation scheme in a single cell downlink heterogeneous networks

Rehan Zahid; Atta ur Rahman; Syed Ali Hassan

The need for small-sized and low-powered home base stations such as femtocells has increased with an escalated data demand. Since the downlink traffic is larger in magnitude than the uplink, use of femtocells provides a good solution. Femto-cells not only increase the throughput but also the overall capacity of the system while operating in the same licensed spectrum. Because of their operation in the same spectrum, interference becomes a major problem. In this paper, we study the downlink performance of a heterogeneous network by proposing a Reverse frequency allocation (RFA) scheme by dividing the cell service area into multiple regions and assign frequencies to various cell entities in such a way that the major interference is avoided. RFA scheme not only improves the spectral efficiency by utilizing the complete spectrum within one cell but also eliminates the strong interference due to macro base station on femto users.We analyze and evaluate the achievable performance of this technique for the downlink scenario. Using simulations, we show that under reasonable signal-to-interference plus noise ratio (SINR) values, multiple regions enhance the performance of users by decreasing the overall system outage probability. It is shown that a 4-region RFA scheme provides almost double performance gain over a 2-region RFA scheme for the same set of parameters.


Industrial Lubrication and Tribology | 2015

Innovative technique of measuring follower rotation in real production engine using Gradiometer sensor and the effect of friction modifier

Riaz A. Mufti; Rehan Zahid; Farrukh Qureshi; Jawad Aslam

Purpose – The purpose of this paper is to understand the effect of engine operating conditions and lubricant friction modifier on direct acting tappet rotation. In this research work, novel method of measuring engine tappet rotation speed has been developed. The technique is so novel. It allows the measurement on real production engine with no modification to the engine tappet bore. Also, In this paper, the effect of engine operating conditions and the effectiveness of friction modifier on tappet rotation is reported. Design/methodology/approach – For the very first time, for the purpose of measuring follower rotation in a real production engine, a 4 × 6 mm2 electronic chip called Gradiometer is mounted outside the tappet housing, allowing the monitoring of tappet rotation speed without the need to machine a hole in the tappet bore. This novel technique is adopted on Mercedes Benz OM464 engine to study the effect of engine conditions and lubricant chemistry on tappet performance. Findings – The main outco...


international conference on wireless communications and mobile computing | 2015

Stochastic geometry-based analysis of multiple region reverse frequency allocation scheme in downlink HetNets

Rehan Zahid; Syed Ali Hassan

Femtocell access points (FAPs) are low-powered and small-sized base stations that provide high data rates and coverage to the indoor users. Because of their operation in the same spectrum as that of macrocells, interference becomes a major problem. Reverse frequency allocation (RFA) is one of the robust schemes, which mitigate the interference by transfering it from the macrocell base station (MBS) to the macrocell user equipments (MUEs), particularly in the downlink. In this paper, we provide a multiple region 2-tier downlink model using the RFA scheme. We derive a closed-form expression for the coverage probability of femtocell user equipment (FUE) using different RFA schemes under open access mode. Where FAPs and MUEs are modeled as independent Poisson point process (PPP). Using simulations, we show that for reasonable values of signal-to-interference ratio, multiple regions enhance the coverage probability of an FUE. It is shown that a 4-region RFA outperforms the other RFA schemes at different densities of FAPs and MUEs as well as for different values of threshold for the same set of parameters.


Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | 2018

The effect of particle size on the dispersion and wear protection ability of MoS2 particles in polyalphaolefin and trimethylolpropane ester

Mubashir Gulzar; Khalid Mahmood; Rehan Zahid; Abdullah Alabdulkarem; H.H. Masjuki; M.A. Kalam; M. Varman; N.W.M. Zulkifli; Pervaiz Ahmad; Mss Malik

The effect of particle size and surfactant on dispersion stability and wear protection ability was experimentally evaluated for polyalphaolefin (PAO 10) and bio-based base oil (palm trimethylolpropane ester) added with molybdenum disulfide (MoS2) particles. Nanolubricants were developed by adding 1u2009wt% of MoS2 particles that varied in size. In addition to the variation in particle size, an anionic surfactant was also used to analyze its interaction with both types of nanoparticles for stable suspensions and for the related effects on the antiwear characteristics. The wear protection characteristics of the formulations were evaluated by four-ball extreme pressure tests and piston ring on cylinder sliding wear tests. The wear surfaces were analyzed by scanning electron microscopy along with an energy-dispersive X-ray and an atomic force microscopy. The MoS2 nanoparticles with a nominal size of 20u2009nm exhibited a better load-carrying capacity, while better sliding wear protection was provided by nanoparticles with a nominal size of 50u2009nm.

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Riaz A. Mufti

National University of Sciences and Technology

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Robiah Yunus

Universiti Putra Malaysia

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Muhammad Usman Bhutta

National University of Sciences and Technology

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Naqash Afzal

National University of Sciences and Technology

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