- Open Access
Utilization of unattended waste plastic oil as fuel in low heat rejection diesel engine
© The Author(s) 2019
- Received: 27 February 2018
- Accepted: 2 November 2018
- Published: 19 March 2019
This experimental work analyzes the usage of 100% of Waste Plastic Oil (WPO) in low heat rejection (LHR) diesel engine without diesel. For this purpose, the hardware components of conventional diesel engine were coated with lanthana-doped partially stabilised zirconia, to a thickness about 300 μm by plasma spray coating technique. WPO was produced in a research facility scale setup by pyrolysis method. Coated and uncoated engines were tested with WPO and the outcomes were compared with diesel. Results authenticate the objective of this study and shows enhancement in performance and diminution in specific fuel utilization. The reduction in emission with exception of NOx was noticed in lanthana-doped partially stabilised zirconia coated engine than that of uncoated diesel engine.
- Lanthana-doped partially-stabilized zirconia
- Waste plastic oil
Worldwide most suitable and usable power generation unit is diesel engine because of its high fuel conversion efficiency, reliability and robustness. Diesel engines were accepted in automobile, agricultural sectors due to their superior thermal efficiency and easiness of handling. Hence, the consumption of fossil fuel increased tremendously for the last 40 years. This increases the demand and cost of the fossil fuels. Burning of fossil fuel emits large amount of pollutants, which causes the air pollution and affect the environment severely [1–4]. In this regard, a viable solution for fossil fuel depletion and simultaneously addressing the reduction of engine exhaust gas emission can be found with alternate fuels. The use of vegetable oils in diesel engine has been enormously increased, as it can be produced in large scale and eco-friendly. However, utilization of vegetable oil directly in the diesel engine produces lower performance because of its higher viscosity. So transesterification process is required for reduction of viscosity of vegetable oil . However, transesterification process does not improve the biodiesel properties as closer to diesel fuel. Several researchers have pointed out that blends of biodiesel and diesel have improved the performance and reduced the emission of diesel engine, but still the usage of diesel fuel is not minimized. On the onset, availability, predictability and storage are more difficult for biodiesel than other alternative fuels. Nowadays plastics are mostly used in industrial and household sectors due to its various attractive qualities and low cost. In spite of these advantages, the plastic wastes have large number of natural complexities. The enormous use of plastic has made a lot of waste plastic and it has ended up in all landfills. It presents a major issue in disposing them in view of their non-degradable nature [6, 7]. So, production of straight waste plastic oil (WPO) from waste plastic by pyrolysis process that can be used in diesel engine is a feasible solution. From this the dual benefit of getting energy from wastes and solving disposal problem can be achieved . Kumar et al. reported that brake thermal efficiency (BTE) of WPO at all loads conditions was lower than that of diesel fuel . Kaimal et al. reported that at higher load, thermal efficiency of WPO blends with diesel is lower than that of diesel because of its lower calorific value . Gungor et al. evaluated the performance of multi-cylinder, combustion chamber- compression ignition (CI) engine fueled by WPO. They found that BTE of engine has slightly decreased by using 100% WPO. Increase of carbon monoxide (CO) and oxides of nitrogen (NOx) was observed . Panda et al. used WPO in diesel engine and they reported that engine power was reduced to 16% with a 20% blend and reduction of 50% with a 40% blend . Mani et al. concluded that 100% WPO can run the diesel engine without any modifications, but CO and hydro carbon (HC) emissions were higher and smoke was decreased by 40% compared to diesel .
Lapuerta et al. tested the CI engine fueled by waste cooking oil mixed with diesel and reported that particulate matter (PM) was decreased at both low and medium load ranges and exhibited no progressions at higher loads .
LHR engine exhaust emission compared to conventional engine fueled with biodiesel using plasma spray coating technique
Standard/base engine specifications
Exhaust gas temperature
Constant speed and variable load
Higher at all loads
lanthanum doped partially stabilised zirconia zirconate
Constant speed and variable load
Higher at all loads
Kirloskar, AV 1
Constant speed and variable load
At higher load CO increases
At higher load CO increases
Ford 6.0 lt. T/C, intercooling, direct injection
Literature review revealed that enhancement of engine efficiency, reduction of pollutant emissions, lower fuel consumption, and removal of cooling system from engine are the main advantages of LHR engine . In order to reduce the negative aspects of 100% WPO in diesel engine, TBC coating is needed on diesel engine hardware. The main objective of this study is the utilization of 100% of WPO in diesel engine without using diesel. In this investigation, the usability and constancy of 100% of WPO as fuel in a lanthana-doped partially stabilized zirconia coated diesel engine and uncoated diesel engine were investigated. Operating parameters were compared between coated and uncoated diesel engines.
Making of WPO from waste plastic
Properties of diesel and waste plastic oil
Density@ 15 °C (kg m−3)
Kinematic viscosity @ 40 °C (cSt)
Flash point (°C)
Fire point (°C)
Gross calorific value (kJ kg−1)
Conversion of conventional engine in TBC engine
LHR engine performance is based on the properties of the coating materials. TBC materials must possess the following properties such as lower thermal conductivity, lower specific heat, higher strength, higher thermal shock resistance, fracture toughness, higher expansion coefficient, higher temperature capability, chemical inertness and high resistance to erosion and corrosion. Survey of literature reveals that various ceramic materials are being utilized for TBC in LHR engines. Coating materials used so far in CI engine include zirconium oxide (ZrO2), calcium zirconite (CaZrO3), partially stabilized zirconia (PSZ), Al2O3, mullite and TiO2, yttria stabilized zirconia (YSZ), among others .
However, the usage of zirconium in LHR engine is limited. Pure zirconia modifies its phases in three crystal forms at various temperatures. At temperature more than 2350 °C it has a cubic structure, between 1175 to 2370 °C it has tetragonal structure and below 1160 °C, it is transformed into monoclinic structure. Transformation from tetragonal to monoclinic is rapid due to the change in temperature. In this transformation, the volume is increased from 3 to 6% thereby making cracks in the material . In a CI engine, operating temperature varies from 600 to 2000 °C. Hence pure zirconia is not a suitable material for LHR engine. The crystal structure changes of zirconium can be prevented by mixing with suitable metal oxides, which will retard or reduce these crystal structure alterations and increase the stability of cubic structure .
Zirconia is mixed with metal oxides of MgO or Y2O3 in order to maintain its cubic structure at various temperatures. Cubic stabilized zirconia is a valuable ceramic material, which does not experience destructive phase changes throughout heating and cooling. In the present investigation, magnesium oxide is selected to mix with zirconium based on the availability and cost. Zirconia is mixed with 10% MgO and then it is called PSZ.
PSZ is widely used as TBC material, due to its lower thermal conductivity and phase stability at working temperatures more than 1200 °C . However, addition of 10% MgO increases the tendency of sintering, hence improvement of the quality of the coating is done by doping small amount of Lanthanum Oxide (La2O3) with PSZ. This will reduce the thermal conductivity and resistance to sintering. Therefore, in the present investigation, coating material is selected as PSZ with addition of La2O3. The coating on the engine components was done by using plasma spray method. This method is most suitable, precise and effective for coating on the diesel engine combustion hardware components.
Plasma spray method comprises of material as powder infused through a high temperature plasma fire, where it is quickly warmed and speedup the process. This hot material impact on the substrate surface quickly chills off and immediately starts framing of coating. Plasma gun comprises of copper anode and tungsten cathode and both are water-cooled. Plasma gas streams around the cathode and through the anode form a nozzle. In this plasma spray method argon is utilized as bearer gas and hydrogen is utilized as auxiliary gas.
CI engine combustion chamber components were coated by lanthana-doped PSZ for a thickness of 300 μm over a 100 μm thick Al2TiO5 bond coat by plasma spray method. Before coating, the surface has to be sand blasted to make outside roughness of 5 μm, which is measured by using roughness tester PCE-RT 11. Then it was cleaned by anhydrous ethanol and dried in cool air. Al2TiO5 powder was injected to get the first coating of bond on the sand blasted substrate. This warm material contacts on the substrate surface to form 100 μm thick coating.
In the same way the next layer of lanthana-doped PSZ coating of thickness 300 μm was done. Thus, the total coating thickness comes to 400 μm. The same process is followed on all other combustion elements. To keep the compression ratio of the engine as same before and after coating, a suitable grinding should be done on engine components before coating.
Specifications of the engine
Kirloskar oil engines limited
Type of Engine
Vertical, 4-Stroke, DI-CI engine
Method of loading
Eddy current dynamometer
Bore and stroke
87.5 × 110 (mm)
List of instruments and their accuracy along with percentage of uncertainties 
Type & manufacturer
Strain gauge, Sensotronics Sanmar
± 10 N
Magnetic pickup principle
± 10 rpm
Fuel flow measurement
Differential pressure transmitter
± 0.1 cm3
AVL exhaust gas analyser, Austria
AVL exhaust gas analyser, Austria
AVL exhaust gas analyser, Austria
± 12 ppm
AVL smoke meter
± 1 HSU
± 1 °C
Pressure pick up
Magnetic pickup principle
± 1 kg
Crank angle encoder
Magnetic pickup principle
± 1 deg
BTE is the direct indication of diesel engine conversion capacity of heat from fuel to mechanical energy. BTE of the diesel engine fueled by WPO and diesel for LHR and uncoated engine are shown in Fig. 2b. Engine BTE depends upon the heating value and specific gravity of the fuel. It is concluded that BTE increases with brake power for diesel and WPO in LHR engine than uncoated engine. This is because of heat transferred through combustion elements is reduced by ceramic coating and also increase in in-cylinder gas and wall temperature . Hence, combustion is developed and thus improves the BTE. Another reason is that reduction of BSFC leads to improvement in BTE. It is also noticed that at higher load, BTE for WPO in coated engine is 33% and it is 2% higher than that of diesel in coated engine. This may be due to additional quantity of fuel burnt at higher load . It is also noticed that oxygen presents in the WPO causes complete combustion.
Exhaust gas temperature (EGT)
Figure 2c exhibit the effect of EGT with brake power for LHR and conventional engine fueled with diesel and WPO. EGT increases with increase of brake power for LHR engine but not in conventional engine. This might be the reason of decrease in heat losses with effect of ceramic insulation which transfers heat into exhaust gas . EGT rises as a result of combustion which extends from power stroke to the exhaust stroke in the cylinder . It is viewed that EGT of WPO in LHR engine is 410 °C and it is 15 °C less than that of WPO in conventional engine.
The effects of CO emission with brake power on LHR and uncoated engine fueled by WPO and diesel are indicated in Fig. 2d. CO is a toxic gas produced because of poor combustion due to insufficient oxygen supply. Low flame temperature and rich mixture are also the reasons for higher CO. The CO emission is reduced with increase of brake power for both engines, but after 80% of load, the CO emission is suddenly raised and it reaches maximum for coated and un-coated diesel engine fueled by diesel and WPO. It is because of accumulation of more fuel at higher load and insufficient combustion time. At full load, CO emission of WPO is 0.22%, which is 0.12% lesser than that of diesel in conventional engine. This is due to more oxygen present in the WPO, which leads to better combustion and oxidation of CO into CO2 . It is also found that at the maximum load, CO of WPO in LHR engine is 0.2%, which is 0.02% lesser than that of WPO in the conventional engine. It is because of higher temperature of gas that reduces the level of pre-mixed combustion. It leads to decrease the initial formation of CO. WPO exhibits longer ignition delay due to its lower cetane number and higher aromatic content, thus it shortens the combustion period.
Effects of NOx emission on coated and conventional engine fueled with diesel and WPO are indicated in Fig. 3c. From the figure it is observed that NOx continuously increases with brake power due to increase of in-cylinder heat. The NOx emission is higher in LHR engine than uncoated engine , due to ceramic coating that increases the combustion temperature and combustion duration. The NOx emission of LHR engine fueled with WPO at higher load is 980 ppm, which is 90 ppm higher than that of WPO in conventional engine. This is due to the ceramic coating which causes shorter ignition delay and contents of oxygen molecules in WPO lead to an increase in NOx emission.
Normally, smoke is not visible from engine exhaust and it is visible because of sluggish or incomplete combustion and as a negative indicator of engine operation. The effects of smoke on coated and conventional engine fueled with WPO and diesel are shown in Fig. 3b. Smoke opacity increases with increase of brake power, this is because of quantity of fuel supplied for every unit time increases . The smoke is less in LHR engine fueled by WPO than that of conventional engine. This is as a result of higher in-cylinder gas and wall temperature than that of conventional engine. Also, at higher load in LHR engine, smoke emission of WPO is 41 Hartridge Smoke Unit (HSU), which is 10 HSU lesser than that of diesel in conventional engine. This is because of more oxygen present in the WPO that leads to better combustion.
Ignition delay is one of the significant parameter for analyzing the combustion process in diesel engine. The intermediate time period between start of fuel injection and start of combustion is calculated in diesel engine and it is termed as ignition delay. Effect of ignition delay with brake power on coated and uncoated engine fueled by diesel and WPO is indicated in the Fig. 3d. Ignition delay is lower for WPO than diesel in both engines due to lower compressibility and higher viscosity of WPO. . Further, the ignition delay for WPO in LHR engine decreased from 10 to 8 °CA, as brake power increased from zero to 4 kW. This is lower than that of WPO fueled in uncoated diesel engine, which has decreased from 13 to 7 °CA. This is because of higher combustion temperature by ceramic coating that leads to shorten ignition delay.
Peak cylinder pressure
Effect of HRR on coated and conventional engine fueled with WPO and diesel is indicated in Fig. 4b. HRR was estimated based on the average data of 100 cycles of engine operation. At the beginning of combustion, HRR is lower for all fuels. This might be due to vaporization of fuel through ignition delay period which decreases the temperature . In premixed combustion stage, heat release rate is more for uncoated engine for both fuels compared to coated engine. This is on account of longer ignition delay that admits more quantity of fuel. Hence, higher HRR was achieved . HRR for WPO and diesel in uncoated engine are 50 and 46 J °CA− 1 respectively. This is because of higher fuel-air ratio of WPO as compared to diesel. However, in diffusive combustion phase, the combustion is progressed and higher HRR is observed for LHR engine for both fuels. This might be due to insulation effect of coating that increases the in-cylinder temperature.
The main objective of this study is that diesel engine can be run by alternative fuel without using diesel that has been achieved through LHR engine fueled with WPO. For that purpose, engine combustion hardware elements were coated by ceramic material of lanthana-doped PSZ. More heat has accumulated in the combustion chamber with the effect of insulation coating, thus enhancing the performance and reducing the emission drastically.
Pyrolysis process was used for preparation of WPO.
The significant improvement in BTE in LHR engine fueled with neat WPO was achieved. At higher load, BTE for WPO in coated engine is 33% and it was 3% higher compared to WPO in uncoated engine.
The BSFC and CO emission were lower in LHR engine than in conventional engine for both fuels.
The HC emission and smoke of LHR engine were less than that of conventional engine. This is because of more amount of heat accumulated in the combustion chamber.
The NOx emission was higher for WPO in uncoated engine due to higher oxygen content of WPO. NOx emission further increased in LHR diesel engine fueled with WPO. This is on account of higher in cylinder temperature caused by insulation coating.
In short, WPO fueled LHR diesel engine is better as compared to diesel engine fueled with diesel except in higher NOx emission.
The authors would like to thank and express gratitude to Dr. R. Senthil, Dean, University College of Engineering, Anna University, Villupuram, Tamilnadu, INDIA and also peers who were instrumental in providing their rich experience.
SE is the main author who wrote the ideas and interpreted the results of the manuscript. BP is responsible for the data collection, analysis and presentation. Both authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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