Quantifying the ignition delay of single wall carbon nanotube emulsified marine fuel oil influencing the combustion and diesel engine efficiencies

The importance of hydro-carbon-based liquid fuels burned by diesel engines in meeting the mechanical power requirement remains up-to-date due to cost, power and environmental problems. It is known from scientific publications that the added micro additives prolong the combustion process of bio fuels, increase the combustion efficiency by approximately 10%, and have positive results in the quantity and quality of the combustion products released into the atmosphere. On the other hand, the developing technology sheds light on the production, control and use of nanomaterials in this field. The presented work is one of these ongoing efforts. Ignition delay (ID), being the beginning of the combustion phase in diesel engines, is a multifunctional polynomial that contains irreversible chain events effecting combustion and engine efficiency. The events, factors and parameters involved in the functions that make up this polynomial are important issues studied to improve the combustion quality of the fuel. This work was done in two consecutive stage that complement each other. In the first stage, machine geometry, fuel / air relationship and cylinder dynamics, which was consider to have a dominant role in the development of ignition delay, were examined at the necessary level. Respectively Molecular-particle ballistic collision density, breakdown of Van der Waals bonds, phonon propagation, in-cylinder temperature increase and activation energy were considered as the effective events that constitute the ignition delay in this study. Stage 2 covers numerical calculations and analysis of heat dissipation, induced power, torque, braking power, fuel consumption, machine efficiency and combustion efficiency, which are affected by the prolonged ignition delay of the test fuels obtained by adding different amounts of SWCNT and MWCNT into the base fuel. It was considered that the ignition delay of carbon nanotubes bundled with fuel molecules would contribute to the kinetic energy and momentum of the injected fuel droplets in the spontaneous combustion phase, where chemical kinetics came to the fore, and would increase the molecular-particle ballistic collision density by penetrating into the turbulent environment more quickly and easily. With this assumption, it was considered that carbon nanotube particles to be added to DMA-ISO8217 selected as the base fuel could increase the combustion efficiency by extending the ignition delay. In order to determine the possible improvement in ignition delay and combustion efficiency, although the precise measurement procedures were not yet finalized, single and multi-walled carbon nanotubes with high thermal conductivity and heat dissipation properties compared to other materials were selected as additives, DMA-ISO8217 considered as the base fuel, was supplied from TÜPRAŞ in precisely weighed 4-liter bottles. Single and multi-walled carbon nanotubes were produced with 95% purity in 1g and 2g, respectively, by NANOGRAFİ Co. with chemical vapour deposition (CVD) method. The physical properties of the single-walled carbon nanotube in this production were specified in the certificate. However, the physical dimensions of multi-walled carbon nanotubes could not be measured due to the complexity of the graphene sheets and lack of measurement technology and methods. Two single and two multi-walled carbon nano tubes of different weights were added to 4 pieces of 4-liter base fuel and weighted precisely within 0.001 precision at Piri Reis University Physics Laboratory. The samples obtained were mixed for one hour at a speed of 25000 rpm. The properties of the obtained test-fuels were again determined as certified in TÜPRAŞ Laboratories. Measurements, made with test fuels, were carried out under the same method and conditions using water-cooled, natural aspirated, direct injection, single-cylinder, high-speed 3LD510 Lombardini Diesel engine in the Automation Laboratory of Yıldız Technical University. Engine speed, in-cylinder pressure, torque, fuel and air consumption values were measured by sensors. Measurements were repeated five times for each test fuel at full load, in the range of 1300-3000 RPM. The measured values were recorded in the AVL program database. The amount of heat release, indicated power, brake-power, mechanical and thermal efficiency values were calculated numerically using the data obtained from experimental measurements. The crank angles of injection, spontaneous combustion and auto-ignition in the physical and chemical ignition delay stage of each test fuel were determined from the measurement charts and compared. The difference and deviations with the base fuel were determined. Effects of extended ignition delay of test fuels with different amounts of SWCNT and MWCNT, on the indicated power (Pi), heat release (Q), torque (τ), fuel consumption (foc), braking power (Pb), mechanical efficiency (ηmec) and thermal efficiency (ηth) were analyzed with binary correlations. In the experiments, the ignition delay of all test fuels containing different amounts of SWCNT and MWCNT and depending on the engine speed was prolonged by shifting 0.5-1.5 degrees according to DMA-ISO8217. Considering the amount of SWCNT and MWCNT added test-fuel consumed at each speed stage and the torque obtained, the calculated brake-power was relatively higher than the base fuel DMA-ISO8217, and the thermal efficiency increased by 4-6%