Evaluation of combustion, performance, and emissions of optimum palm–coconut blend in turbocharged and non-turbocharged conditions of a diesel engine
Introduction
The global energy crisis, which is attributed to the depletion of fossil fuels and increasing environmental concerns, has motivated scientists to seek eco-friendly alternative sources of energy. To address this problem, researchers have been conducting studies for the last few decades [1], [2], [3], [4], [5], [6], [7]. One solution is the use of biodiesel, which is nontoxic and biodegradable [8], [9]. The use of biodiesel minimizes greenhouse gas emission because of closed carbon cycle [10], [11]. Biodiesel can sometimes extend engine component life [12], [13] and can be used in existing diesel engines without any modification [14]. However, minor modifications in engine fuel line components are sometimes recommended because biodiesel possesses some fuel properties that affect these components [15].
Many researchers conducted theoretical and experimental studies to improve (optimize), predict, and characterize biodiesel properties. Benjumea et al. [16] established prediction equations for kinematic viscosity, density, heating value, three different points of distillation curve, and calculated cetane index as a function of the volume fraction of biodiesel in the blend. Later, they validated the equations experimentally, which shows that except for viscosity, other properties of binary mixture take the form of an arithmetic volume average. Alptekin and Canakci [17] experimentally studied the improvement of different fuel properties, namely, kinematic viscosity, density, pour point, flash point, and distillation characteristics in five different biodiesels (sunflower, canola, soybean, cottonseed, and corn oil) by blending with petroleum diesel at different ratios. Hussan et al. [18] tailored the viscosity of biodiesel by ethanol and a mathematically derived optimum formulation. They added this optimum palm biodiesel–ethanol blend at varying proportions (0–30%) with No. 2 diesel and studied various key fuel properties such as kinematic viscosity, derived cetane number (CN), flash point, cloud point, pour point, heating value, oxidation stability, specific gravity, and other properties. Some researchers also tried to improve fuel properties by using different additives. Rizwanul Fattah et al. [19], [20] and Palash et al. [21] used different antioxidant additives to improve oxidation stability and tested their effect on engine performance and emission. Imtenan et al. [22] reduced the density and increased the oxygen content of the blends by using oxygenated additives, and they tested their engine performance and emission characteristics.
Previous studies on biodiesel indicate that its use in unmodified engines reduces brake power and increases fuel consumption. Xue et al. [23] studied more than 150 research endeavors and found that more than 50% confirmed higher thermal performance (efficiency), and approximately 45% indicated higher NOx emission, whereas more than 50% showed low PM, CO, and HC emission with the use of biodiesel blends. The low calorific value of biodiesel results in higher brake thermal efficiency. Carraretto et al. [24] tested a six-cylinder diesel engine with diesel and biodiesel blends at different ratios and found a decrease in performance and CO emission but an increase in NOx emission. To aggregate the advantages of the high-ignition quality of palm and the high-oxygen content of coconut, the combined blend of this two biodiesels at a specific ratio was experimentally studied by Habibullah et al. [25]. They concluded that depending on performance and emission parameters, the combined blend shows superior performance and emission over individual biodiesel blends.
Although the use of additive-added blends improves some performance or emission aspects, these blends affect other parameters adversely. In addition, they are associated with high production costs. This study mainly aims to improve engine performance and emission by using biodiesel from a particular feedstock by blending with biodiesel from another feedstock, which has better properties in some aspects compared with the previous ones and thereby forming a binary mixture with improved properties. Although some research previously studied binary biodiesel mixture, they used common mixture ratios [26], [27]. However, in this study an optimized ratio of binary biodiesel mixture, which improves overall fuel properties has been used. The ratio was obtained using MATLAB optimization tool, a method which has not been adopted by earlier studies. Palm and coconut biodiesel were chosen because of their superior characteristics, such as a high CN, high oxygen content, good ignition and combustion characteristics, and low pollutant emission [28], [29]. In addition, Malaysia is one of the largest palm producers in the world, and its government has decided to use 40% (approximately 6 million tons) of the total palm produced annually as biodiesel. Later, experimental study was conducted to determine the effect of 20% blend of optimum binary biodiesel mixture with diesel on engine combustion, performance, and emissions.
Section snippets
Optimum blending ratio calculation
Experiments were conducted by using blends of palm and coconut-based biodiesel. Many researchers found that the most important fuel properties, such as density, kinematic viscosity, oxidation stability, flash point, calorific value, and CN, vary linearly in the case of multiple biodiesel blends [16], [17], [30], [31]. Thus, the linear relationship among fuel properties was considered to determine the optimum blending ratio, for which MATLAB optimization tool was used. The optimization tool is a
Improvement of fuel properties
Engine performance and emission are directly affected by the physiochemical properties of fuel. These properties include density, viscosity, flash point, oxidation stability, CN, iodine value, and acid value. These properties indicate fuel quality. Among these properties, density, kinematic viscosity, oxidation stability, flash point, calorific value, and CN served as the focus of the researchers to determine fuel quality [32], [33], [34]. Different standards, such as ASTM, BS, and ISO, are
Fuel properties
From the experimental fuel properties of CB, PB, and OD (Table 2), the densities of all biodiesels are significantly close to one another and approximately 3–3.5% higher than the density of petroleum diesel. The kinematic viscosities of CB and PB are also very close to each other. A large variation is observed in terms of induction time. PB had an induction time close to the ASTM standard (3 h), whereas CB had the highest induction time (5.12 h). The flash points of all biodiesels are
Conclusion
This study was conducted to improve several fuel properties of palm biodiesel by using the binary mixture of palm and coconut biodiesel through an optimum blend ratio derived using MATLAB. Later, 20% blend of this binary mixture (PC) with OD was tested in a diesel engine to compare the performance and emission characteristics of 20% palm biodiesel blend with OD as well as OD alone. The following conclusions are drawn as a summary of the experiment:
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Two biodiesels can be blended to formulate a
Acknowledgement
The authors would like to acknowledge University of Malaya for financial support through High Impact Research grant titled: “Clean Diesel Technology for Military and Civilian Transport Vehicles” having grant number UM.C/HIR/MOHE/ENG/07.
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