Experimental Study of the Influence of Nanoparticles Additive to Diesel Fuel on the Emission Characteristics

The present experimental work is conducted to examine the influence of adding Alumina (Al2O3) nanoparticles and Titanium oxide (TiO2) nanoparticles each alone to diesel fuel on the characteristic of the emissions. The size of both Alumina and Titanium oxide nanoparticles which have been added to diesel fuel to obtain nano-fuel is about 20 nm and 25 nm respectively. Three doses of (Al2O3) and (TiO2) were prepared (25, 50 and 100) ppm. The nanoparticles mixed with gas oil fuel by mechanical homogenous (manual electrical mixer) and ultrasonic processor. The study reveals that the adding of Aluminum oxide (Al2O3) and Titanium oxide (TiO2) to gas oil (Al2O3+DF) and (TiO2+DF) improves the emissions characteristic of engine such as CO emissions are reduced by 34.28% and 20.5% for TiO2+DF and Al2O3+DF respectively at 25ppm, the emissions of CO2 increased by about 1.75% and 2.27% for TiO2+DF and Al2O3+DF respectively at 100ppm, the emissions of NOx decreased by about 37.7% and 12.2% for TiO2+DF and Al2O3+DF respectively at 25ppm and the emissions UHC decreased by about 16.9% and 13.5% for TiO2+DF and Al2O3+DF respectively at 25ppm.


Introduction
Diesel fuel is one of the world's largest sources of pollutants, where the burning of diesel fuel in compression ignition engine producing unburned hydrocarbons (UHC), nitrogen oxides (NOx) and carbon monoxide (CO). Additionally, produce small amounts of sulfur oxides (SOx) [1]. However it also, produces carbon dioxide (CO2) which is a friend of the environment, oxygen (O2) and water vapor (H2O). So the researchers using several additives to diesel fuel especially the nanoparticles in recent years to resolve the problem of emissions [2]. The nano-fuel can define as a mixture of both diesel fuel and dosage of nanoparticles, which has different properties than net diesel and called also modified diesel. [3] The studies have shown that the addition of nanoparticles enhances the performance of the engine such as reducing specific fuel consumption and increasing thermal efficiency [4].The enhancement of the surface to volume ratio due to adding nanoparticles leads to decreasing the concentration of pollutants and increasing the rate of reaction [5].The expect reason of making the reaction faster due to a short delay period comparing to pure diesel [6]. Nanoparticles are worked to enhance some physical properties of a lot of fluids including diesel fuel [7].Where, it has been noticed that the nano additive to diesel (nanoparticles+ diesel) improve the fire point, flash point, viscosity, density and the other properties depending on the doses of nanoparticles [8].The particles which are suspended in diesel fuel increase effective thermal conductivity, the surface area of contact [9].Also, reducing the exhaust emission such as unburned Hydrocarbons (UHC), Nitrogen oxides (NOx) and Carbon monoxides (CO) [10]. This present experimental research will study the influence of Alumina (Al2O3) and Titanium oxide (TiO2) nanoparticles on the emission characteristics. Although utilizing nanoparticles in diesel fuel have several advantages, the utilizing nanoparticles may involve several disadvantages such as increase in pumping power, higher viscosity (undesirable level) and block the nozzles due to agglomerate the nanoparticles [11]. There are many types of nanoparticles [12]; these are shown in the table (1).

Experimental Setup
The engine used in the experimental tests is Fiat diesel engine, four cylinders, 4-stroke, direct injection, natural aspirated, closed water-cooled cycle with a displacement volume (3.666 L) and fitted with a hydraulic dynamometer. Figure (2.1) shows the test engine with its equipment. The specifications of engine test are given in table (2). The type of additive nanoparticles is Alumina (Al2O3) and Titanium oxide (TiO2). The selection of doses depends on primary experimental results and researchers' results [13]. The chosen doses are (25, 50, and 100) ppm. The size of both Alumina and Titanium oxide nanoparticles is 20 nm and 25 nm respectively. The nanoparticles blended with fuel each one by mechanical homogenous (manual electrical mixer) for one hour in order to prevent the gathering of particles rapidly and ultrasonic processor UP200Ht (power 200W and frequency 26 kHz) to disperse the nanoparticles and distribute them equally in the base fuel. All the exhaust gases emissions from the engine studied (unburnt Hydrocarbon (UHC), CO2, CO and NOx) are measured by using the gas analyzer. The gas analyzer model AIRREX HG-550 used to measure the exhaust emission by two principles which are Electro-Chemical principle for measuring NOx and O2 and non-dispersive infrared principle for measuring (UHC, CO2, and CO).
The measurements for thermophysical properties of nano diesel and diesel are shown in table (3). Where the viscosity, density and the flash point and fire point were measured for both diesel and nano-diesel at University of Technology/ Department of Chemical Engineering. Cetane number was measured for both diesel and nano-diesel at University of Babylon / Department of Polymer Engineering. The calorific value of diesel and nano-diesel was measured at Middle Refineries Company/ Quality Control Laboratories Department.

Result and Discussion
This section introduces the results obtained from experiments, where the results include:

Carbon Monoxide (CO) Emission
The influence of nanoparticles doses level and types on CO emission for diesel fuel is shown in figure (2) and figure (3).The figures reveal that the CO emission decreases with adding TiO2 and Al2O3 nanoparticles; especially with TiO2 may be because of the delay period of titanium oxide is shorter than alumina which leads to complete combustion [10]. The best dose of nanoparticles is 25ppm for both types. Where, TiO2 and Al2O3 reduce the emissions of CO by 34.28% and 20.5% at 25ppm and 75% load respectively.

Nitrogen Oxides (NOx) Emission
The influence of nanoparticles doses level and types on NOx emission for diesel fuel is shown in figure (4) and figure (5).The two figures reveal that the NOx emission decreases with adding the dose 25 ppm of TiO2 nanoparticles at all loads. While, the dose 25 ppm of Al2O3 decreased NOx emission at low loads. The expected reason for increased NOx is high temperature with Aluminum and the availability of oxygen. Furthermore, the thermal conductivity of Al2O3 is larger than TiO2 by four times approximately. Where, the thermal conductivity of TiO2 and Al2O3 are 9W/m.K and 40W/m.K respectively. The biggest decrease of NOx emission with Al2O3 and TiO2 is 12.2% and 37.7% with no load at 25 ppm.   7) shows the variation of Carbon dioxide emission (CO2) with Nanoparticles doses for two types (TiO2 and Al2O3). These figures reveal that CO2 emissions increase by increasing the dose of Nanoparticles due to high thermal conductivity and the presence of oxygen in nanoparticles which in turn makes the combustion complete. The best increase was obtained in CO2 emissions for TiO2 and Al2O3 by 1.75% and 2.27% at 75% load with 100 ppm respectively. The increasing of CO2 emissions gives an indication to decrease CO emissions. The overlap between the two curves of no-load with the curve with load with nanoparticles dose variation due to rich mixture at full load which in turn cause a reduction in CO2 so the overlap occurred.

Unburnt Hydrocarbon (UHC) Emissions
The variation of unburnt hydrocarbon emissions (UHC) with different doses of nanoparticles for two types (Al2O3 and TiO2) is shown in figure (8) and figure (9).The two figures reveal that UHC emissions decrease by adding any dose of Al2O3 nanoparticles at no load and it is increased with all other loads. While the additive TiO2 nanoparticles decrease the emissions of UHC with all loads at all doses including no-load state. The expect reasons, that the equivalence ratio of TiO2 is less than Al2O3 , incomplete combustion of (D+ Al2O3) and the size TiO2 larger than Al2O3 that gives a greater chance to atomize the large droplets of fuel during entering. Finally, the biggest doze was 25 ppm for all loads.

Conclusion
The present paper focuses on the effect of adding Alumina and Titanium oxide to diesel fuel with variable doses on the emission characteristics based on the experimental results from present work. Accordingly, the following conclusions are: