EFFECT OF NANO-GRAPHITE COATING ON SMALL DI DIESEL ENGINE PERFORMANCE

Abstract

Energy efficient systems are always in demand due to the ever widening supply demand gap. Oil import bill of India consumes about one-third of its total expenditure. A large proportion of the oil is consumed by the automobile sector which is a huge burden on our country’s economy. Among the different categories of automobiles, small transport utility vehicles sector is the fastest growing sector. To control fuel consumption and pollution, it is necessary to improve the engine technology to provide more efficient vehicles in terms of their engine performance. Therefore use of technological advancements to reduce engine power losses is of vital importance, which directly improves the engine performance. Amongst the engine power losses, friction is one of the major contributors. It is therefore desirable to make an attempt to minimize friction in the engine. Internal combustion engine is the heart of the automobile as it is the sole power source which runs the vehicle. Its performance plays a major role and recently nanotechnology solutions are being explored for engine development technology. This is a modern challenge and a successful real-scale application of suitable nanomaterial-coating could lead to significant engine performance enhancements. In order to improve performance of IC engine, its combustion chamber would be coated with appropriate nanomaterials and then tested for its performance in terms of friction, mechanical efficiency, fuel consumption, and emissions. In the present work, an attempt is made to enhance performance of the engine with the application of nanomaterials coating on the inner surface of small direct injection (DI) diesel engine's cylinder. The coating in engine component raises expectation of engine performance enhancement which includes increase in fuel economy as well as mechanical efficiency and reduced friction, emission and smoke. In the present investigation, the engine component selected for coating is the engine cylinder alone. As it is well known that, a major proportion of frictional loss in internal combustion engine occurs due to piston-cylinder system. Piston-cylinder system involves piston, piston rings and engine cylinder. And engine cylinder is found to be a common part against which the rubbing action of piston and piston rings takes place. Graphite is the material of choice in the present study because of compatibility considerations and favorable economics. Artificial Neural Network (ANN) modeling was carried out to understand the graphite bulk particle reduction until nanoparticle formation during mechanical milling. Such an exercise was necessary to optimize the particle size reduction process such that cumbersome intermediate particle size sampling and over-milling can be avoided. The milling experiment was conducted at Abstract ii two different speeds 200 rpm and 250 rpm for various hours of run with same initial particle size of graphite. The data was used to develop an ANN model to predict the average particle size as a function of milling time. The ANN model was developed in MATLAB environment (version 8). The best performance of training was found with a single hidden layer comprising of 12 nodes. Based on the ANN model, trial runs were carried out for 70 hrs of milling at jar rotation speed of 200 rpm for synthesis of graphite nanoparticle with less contamination. It had been noticed that on continuous running of jar at higher rotation speed affirm higher amount of contamination while the contamination level is lower in case of lower rotational speed of jar during milling. Contamination level can be further reduced by interrupting the milling at frequent intervals. Electrophoretic deposition process was found to be the most suitable method for coating. The electrophoretic coatings were performed on small coupons of engine cylinder material. After confirming all the coating parameters by several hit and trial outcome, it had been decided to coat the original engine block used in a commercial vehicle. In current coating method electrophoretic electro-chemical cell supplied with a dc voltage of 45-50 V resulted in better graphite nanoparticles (GNPs) thin film deposition. Coated samples did not have enough adhesive strength between substrate and coating particles (GNPs) after removal of external potential. To improve bonding, heat treatment process was adapted based on component working environment as well as nanoparticles behaviour at component working environment. During heat treatment, polymer used during coating evaporates and the distance between graphite nanoparticle layer and the cast iron substrate is minimized which provides an easy path for: (1) interface bonding between carbon atoms of graphitic basal plane and iron atoms of BCC iron in cast iron substrate, and (2) the diffusion of carbon atoms from graphite nanoparticles into the cast iron coupon. Physical appearance of coating on coated sample confirmed the properness of coating, which was also verified at microscopic level. XRD characterization tool is used to check the surface chemical analysis of uncoated and coated sample in different stages. From XRD analysis it is found that the coated sample before and after heat treatment possess GNPs on the surface. The average roughness of the cylinder sample is found to be 0.63 μm. After coating and heat treatment, the sample surface roughness increased to ~0.97 μm. On the other hand, after cleaning the coated sample with engine oil which removed decomposed polymer residue and weakly bonded GNPs, the average surface roughness found to be 0.21 μm. From hardness measurement carried out on coated coupons, it was found that the hardness is higher than that of uncoated sample. The rise in hardness of the coated sample is due to (1) interfacial bonding between GNPs and iron matrix of cast iron substrate, and (2) the diffusion of carbon into iron matrix of cast iron substrate. Abstract iii Understanding wear behavior of the engine cylinder is an important characteristic of its life and performance characteristic. Therefore, scratch test was performed to find the coefficient of friction of uncoated and coated samples. The scratch length of 2 mm was chosen with the travel speed of 0.5 mm/min for both the conditions. From test it was confirmed that the coating have positive effect on coefficient of friction reduction. As the coating is found to be uneven in nature, EDS line-scan analysis at various points was used to measure the coating thickness in-situ. The average coating thickness is found to be ~5.6 μm for 10 min of coating time. After successful coating on cast-iron sample coupons, coating on engine cylinder (originally used in commercial vehicle) was performed with same line of action using a unique design of counter electrode. And entire engine block was placed in a customized furnace with enclosed chamber for maintaining inert atmosphere during heat treatment. After completion of heat treatment the sample was taken out from external furnace chamber and cleaned with engine oil. The coated engine block was installed and underwent testing in a small DI compression-ignition engine test rig. Engine performance testing of small DI compression-ignition engine was conducted in new engines for two cases (1) uncoated engine cylinder and (2) coated engine cylinder in the engine test rig. Engine testing experiments were conducted with three engine parameters (speed, load, coolant flow rate). And it was based on the full factorial design approach and hence one parameter was varied according to its step size while keeping other parameters fixed during the experiments. The experiments are conducted in two phases, firstly to check the engine performance at high speed limit and then at higher loading condition. As both the conditions can not be tested in a single experimental design, so the experiments are divided in two phases. The considered engine performance parameters are brake specific fuel consumption (BSFC), friction power, mechanical efficiency, specific emissions (sCO, sHC, sNO) with respect to indicated power and smoke opacity. The characteristics of the engine are found to be quite similar in both the experimental design, which are as follows: BSFC was found to decrease with increasing load. The fuel consumption measured for the coated cylinder was found to be 5.6 to 12.5 % less compared to uncoated engine. The friction power was found to be 14 % high for uncoated engine block as compared to that for coated engine block. As the load increases mechanical efficiency of the engine was found to increase. The trend is same for coated and uncoated engine, while it was observed that there is some difference between uncoated and coated engine block with regard to Abstract iv mechanical efficiency. For coated engine block it was observed that there is 7.5 to 13.5 % enhancement in mechanical efficiency as compared to the uncoated engine. The specific emission of CO, sCO was observed to decrease as the load increases. And this trend is similar for both uncoated and coated engine blocks. At low load the increase in sCO observed for coated engine block while difference at higher loads was found to be negligible. Even for sHC similar trend was observed. In case of sNO, the decrease in sNO was observed with increase in load. This trend is similar for both uncoated and coated engine blocks with almost constant difference. The specific emission of NO, sNO, for coated engine block was observed to be about 10 % lower. Smoke opacity, was observed to increase as the load increases. This trend has been found to be similar for both uncoated and coated engine blocks. It was observed that the smoke opacity was 5.7 % lower for coated engine block. Optimization of the performance parameters namely BSFC, friction power, mechanical efficiency, sCO, sHC, sNO and smoke opacity was performed for engine performance enhancement. Taguchi and response surface methodology – genetic algorithm (RSM-GA) methods were used for optimization. For Taguchi analysis, experimentations were conducted with L32 (21x49) orthogonal array. The effect of various input factors (engine cylinder, speed, load, and coolant flow rate) on specific engine output parameters were described with the help of factor response plot. The optimization of specific engine output parameters are performed based on their requirement. The coated-block engine have positive impact on BSFC, Friction power, Mechanical efficiency, sNO and smoke opacity while slight negative impact on sCO and sHC. The negative impact is slightly higher at low loading condition only while at higher loading condition there is negligible variation found between coated engine and uncoated engine regarding sCO and sHC. For seven different responses there are seven sets of input, obtained for providing optimal values of each response. So to address the optimization issue properly further multi objective optimization conducted using RSM-GA method. The experimental matrix opted for RSM-GA optimization method was based on Box-Behnken design with three input parameters (speed, load and coolant flow rate) for both uncoated and coated engine cylinder. From optimization results of uncoated engine block and coated engine block it was found that the predicted value of speed is similar for both the cases, while predicted load is higher for the coated engine block, and the coolant flow rate is similar for both the cases. The optimized results were validated using experimentation at the optimized setting value generated through optimization procedure. The variation (in % error) in the experimental and predicted value is found to be less than 10% in both the cases. Abstract v The thesis is organized in six chapters. Chapter 1 provides introductory details of all the matter related to present investigation with outlook on the use of nanotechnology in automotive industry. The literature review is presented in Chapter 2 which gives a state-of-art overview of graphite at nanoscale, nanomaterials coating on IC engine, diesel engine performance studies and lastly, problem formulation. Chapter 3 describes the materials, experimental set-up and methodologies adapted in present study. Chapter 4 includes the synthesis of GNPs and thin film coating of GNPs on the engine cylinder. The details of synthesis of GNPs are followed by the description of coating of GNPs on the engine cylinder. Chapter 5 details the real time testing of coated engine cylinder/block in small DI compression-ignition engine test rig. Finally, the conclusions and recommendations drawn from the present work are contained in Chapter 6.