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The upcoming Bharat Stage VI (BS VI) emission legislation has put enormous pressure on the future of small diesel engines which are widely used in the Indian market. The present work investigates the emission reduction potential of a common rail direct injection single cylinder diesel engine by adopting a holistic approach of lowering the compression ratio, boosting the intake air and down-speeding the engine. Experimental investigations were conducted across the entire operating map of a mass-production, light-duty diesel engine to examine the benefits of the proposed approach and the results are quantified for the modified Indian drive cycle (MIDC). By reducing the compression ratio from 18:1 to 14:1, the oxides of nitrogen (NOx) and soot emissions are reduced by 40% and 75% respectively. However, a significant penalty in fuel economy, unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are observed with the reduced compression ratio.

In a direct-injection (DI) engine, charge motion and mixture preparation are among the most important factors deciding the performance and emissions. This work was focused on studying the effect of injector positioning on fuel-air mixture preparation and fuel impingement on in-cylinder surfaces during the homogeneous mode of operation in a naturally aspirated, small bore, 0.2 l, light-duty, air-cooled, four-stroke, spark-ignition engine modified to operate under the DI mode. A commercially available, six-hole, solenoid-operated injector was used. Two injector locations were identified based on the availability of the space on the cylinder head. One location yielded the spray-guided (SG) configuration, with one of the spray plumes targeted towards the spark plug. In the second location, the spray plumes were targeted towards the piston top in a wall-guided (WG) configuration so as to minimize the impingement of fuel on the liner.

Experimental investigations relating to the performance and emission characteristics under idling conditions of a three cylinder passenger car spark ignition engine operating on a conventional carburettor and a developed single point gasoline fuel injection system are described in this paper. The idling performance at different engine speeds was studied by carrying out comprehensive engine testing on a test bed in two phases. In the first phase, experiments were conducted on an engine fitted with a conventional carburettor whilst they were extended to the engine provided with a developed electronic single point fuel injection (SPI) system, whose fuel spray was directed against the direction of air flow. The injection timing of the SPI system was varied from 82 deg. before inlet valve opening (or 98 deg. before top dead center) to 42 deg. after inlet valve opening (or 26 deg. after top dead center).

In this work, a 7.45 cc capacity glow plug based two-stroke engine for mini aircraft applications was evaluated for its performance, emissions and combustion. It uses a fuel containing 65% methanol, 25% castor oil and 10% nitromethane by volume. Since test rigs are not readily available for such small engines, a reaction type test bed with low friction linear and rolling element bearings was developed and used successfully. The propeller of the engine acted as the load and also the flywheel. Pressure time diagrams were recorded using a small piezoelectric pressure transducer. Tests were conducted at two different throttle positions and at various equivalence ratios. The brake thermal efficiency was generally in the range of 4 to 17.5% depending on the equivalence ratio and throttle position. IMEP was between 2 and 4 bar. It was found that only a part of the castor oil that was supplied participated in the combustion process.

A novel, fully mechanical, simple, compact and cost effective variable valve timing system for two-wheeler application was developed. The details of the system and the performance are discussed. The system uses flyweights to exert a force on a cam, which floats on a shaft against a spring. The movement of the cam is axial and rotational due helical groves on the shaft. The system could start retarding the cam phasing after a predetermined speed. The system when implemented on a small scooter engine of 125 cc resulted in an increase in the volumetric efficiency at low speeds by 8%. The torque was improved by 10%. There was a reduction in the fuel consumption due to reduced throttling losses and leaner mixtures. When the system was implemented on a two-wheeler and tested on a chassis dynamometer on the Indian Driving Cycle a reduction in fuel consumption of 5% was noted. The emissions were also within limits.

Valve actuation parameters like lift, opening and closing times affect performance and emissions of an engine. In this work, a new hydraulic variable valve actuation (VVA) concept is explained, simulated and analyzed using MATLAB. The system applies differential hydraulic pressure on two sides of a piston to open the inlet valve. A system of orifices, one of fixed diameter and the other of variable diameter is used to control the differential pressure. Some of the key parameters, which affect the performance of the system, are fluid supply pressure, damping, orifice diameters, displacement of the plunger controlling the orifice and the spring stiffnesses. The variation of parameters like the plunger movement, inlet and exit areas in a certain way was found to reduce the response time as well as increase the lift. It was also observed that the valve lift could be varied from 3.5 mm to 8 mm by just a 1.5 mm movement of the solenoid actuator.

In the case of small SI engines for two-wheelers emission reduction will preferably be achieved through the use of lean mixtures since catalytic converters will increase the cost. In such cases a very close control over the air fuel ratio will be needed. In this work a carbureted 125cc small capacity two-wheeler engine was modified to operate with Port Fuel Injection (PFI) for improved control over the air fuel ratio. A throttle body was specially made to house the injector and a position sensor. A cam position sensor, crank angle sensor, manifold air pressure (MAP) sensor, 60-2 toothed wheel for precise control of the events on the angle basis were used. Extensive tests were conducted with the throttle body and fuel injector to obtain the mathematical models for the inlet manifold and fuel injector. These were used to make the model based controller. The dSPACE - Micro Auto Box platform was used to develop and test the control algorithms. Software was written using SIMULINK.

Exhaust gas recirculation (EGR) is an effective means to reduce NOx emissions in Diesel engines. An innovative concept of EGR admission was developed for diesel engine of heavy-duty application. A 4-cylinder, naturally aspirated, water-cooled engine was selected for experimental investigation. One-dimensional simulation software was used to predict emission and performance parameters. The engine model was initially validated with experimental data and then used for parametric study for EGR. The best EGR flow rates were determined for experimental study, to study the effect of EGR on engine emissions. A significant reduction in emissions of NOx with minimal increase in CO and HC emission was achieved. Based on number of experiments and simulations an innovative EGR system was developed to control flow of hot exhaust back into the intake manifold for NOx reduction.

In this work a two-wheeler two-stroke spark ignition engine was modified to work in the air assisted direct injection (AADI) mode with gasoline as the fuel. Standard mechanical hardware was used. The controller for this system was developed in-house using a FPGA based system-using Labview software. The system controlled the fuel injection, mixture injection, lubricant pump frequency and the spark timing. Preliminary experiments were conducted at 3000 rpm to determine the influencing variables and potential of this system. Mixture injection timing was an important variable. The AADI system reduced short-circuiting of the fuel and the maximum brake thermal efficiency went up from about 21% with the carbureted version to 26%. There was a significant drop in HC levels from about 1500 ppm to 400 ppm with the AADI mode. NO levels went up slightly due to improved combustion.

The homogeneous charge compression ignition (HCCI) engines emit low levels of smoke and NOx emissions. However, control of ignition, which is mainly controlled by fuel composition, the equivalence ratio and the thermodynamic state of the mixture, is a problem. In this work, acetylene was as the fuel for operating a compression ignition engine in the HCCI mode at different outputs. The results of thermal efficiency and emissions have been compared with base diesel operation in the (compression ignition) CI mode. The relatively low self ignition temperature, wide flammability limits and gaseous nature were the reasons for selecting this fuel. Charge temperature was varied from 40 to 110°C. Thermal efficiencies were almost equal to that of CI engine operation at the correct intake charge temperature. NO levels never exceeded 20 ppm and smoke levels were always lower than 0.1 BSU. HC emissions were higher and were sensitive to charge temperature and output.

In this work a novel mixture injection system has been developed and tested on a two stroke scooter engine. This system admits finely atomized gasoline directly into the combustion chamber. It employs many components that were individually developed, fabricated, tested and then coupled together. A small compressor driven by the engine sends pressurized air at the correct crank angle through a timing valve. This is connected to a mechanical injector through a high pressure pipe. Fuel is metered into the high pressure pipe using a standard low pressure injector. The developed mixture injection system resulted in considerable improvements in thermal efficiency and reduction in HC emissions over the manifold injection method at all engine outputs. A considerable reduction in short circuiting losses was seen. The highest brake thermal efficiency achieved was 25.5% as against 23% with the manifold injection system.

Pilot fuel quantity and intake temperature are two important parameters controlling the combustion process in dual fuel engines. Experiments were conducted on a LPG diesel dual fuel engine at various intake temperatures and pilot quantities. Ignition delay, rate of pressure rise, combustion duration and heat release patterns have been presented at low and high loads. An increase in the concentration of the gaseous primary fuel significantly increased the ignition delay. At high outputs the combustion of the gas by flame propagation which follows the ignition process of the pilot and the entrained gas was the dominant feature. However, at low loads combustion of the pilot fuel and the gas entrained in it were only significant.. The rapid combustion of the gaseous fuel at high output conditions, particularly when the intake temperature was high, resulted in rough engine operation.

In this work, a single-cylinder, water-cooled engine was operated in the Homogenous Charge Compression Ignition (HCCI) mode with diesel as the fuel. Conventional as well as Common Rail Injection (CRI) systems were employed to study the influence of different injection strategies. The injection timing was fixed at 90° crank angle bTDC with the conventional injection system for HCCI operation based on brake thermal efficiency. With the conventional system, the BMEP range was 2.2 to 4.3 bar with a single-axial-hole injector. However, in this case, the brake thermal efficiency was about 30% lower than the CI mode. In the case of the CRI system, a specially developed single-hole nozzle with single and multiple injection strategies was used. Here, there was an improvement in the brake thermal efficiency and emissions were also under control. The BMEP range was only 1 to 3 bar.

An electronic system was developed for the control of the injection timing and injected fuel quantity for studies on a passenger car engine. This system can be used to produce maps of these parameters for implementation in an electronic control unit. The complete electronic hardware which included the cam position sensor, pulse shaping, pulse delay and sequencing features was developed and tested. The system could control the injection pulse width for the different cylinders independent of each other. The developed system was used to conduct parametric studies. The results obtained were compared with that obtained from the base carbureted engine. There was a significant improvement in brake thermal efficiency and reduction in HC and CO emissions with the injection system. A retarded injection timing was needed at low loads. The volumetric efficiency of the injection system was much higher than the carbureted version.

Use of vegetable oils in diesel engines results in increased smoke and reduced brake thermal efficiency. Dual fuel engines can use a wide range of fuels and yet operate with low smoke emissions and high thermal efficiency. In this work, a single cylinder diesel engine was converted to use vegetable oil (Jatropha oil) as the pilot fuel and methanol as the inducted primary fuel. Tests were conducted at 1500 rev/min and full load. Different quantities of methanol and Jatropha oil were used. Results of experiments with diesel as the pilot fuel and methanol as the primary fuel were used for comparison. Brake thermal efficiency increased in the dual fuel mode when both Jatropha oil and diesel were used as pilot fuels. The maximum brake thermal efficiency was 30.6% with Jatropha oil and 32.8% with diesel. Smoke was drastically reduced from 4.4 BSU with pure Jatropha oil operation to 1.6 BSU in the dual fuel mode.

A single cylinder, direct injection diesel engine was run on water diesel emulsion at a constant speed of 1500 rpm under variable load conditions. Water to diesel ratio of 0.4 on the mass basis was used. Tests indicated a considerable reduction in smoke and NO levels. This was accompanied by an increase in brake thermal efficiency at high outputs. HC & CO levels, ignition delay and rate of pressure rise went up. The heat release rate in the premixed burn period was higher. When the oxygen concentration in the intake air was enhanced in steps up to 25% along with the use of water diesel emulsion, the brake thermal efficiency was improved and there was a further reduction in the smoke level. HC and CO levels also dropped. NO emission went up due to increased temperature and oxygen availability. An oxygen concentration of 24% by volume was optimal as the NO levels were near about base diesel values.

A personal computer (PC) based electronic governor was developed in this work for a diesel engine. A stepper motor was used to actuate the rack of the inline fuel pump of the engine with a bell crank lever. The digital output of the system was used to control the stepper motor using special hardware. This governor was tested under different steady and transient operating conditions. The electronic governor performed satisfactorily. In most cases the speed settled down in time duration comparable to that with the mechanical governor. The electronic governor could operate with no change in the mean speed with engine output. The performance was very sensitive to the P, I and D parameters of the control software. It was felt that the system could be improved with a stepper motor of finer steps and higher torque.

Experiments were conducted on a single cylinder SI engine fuelled by natural gas. Equivalence ratios varying from 0.7 to 1.0 were used and the spark timing was changed from no knock to high knock conditions. Pressure crank angle data from 160 consecutive cycles was analysed. It was found that coefficient of variation of peak pressure (COVPP) and standard deviation of the angle of occurrence of peak pressure (SDAPP) can be used to set the engine for knock free operation. These parameters show a sudden rise from a minimum value that they attain near a spark timing where knock sets in. When the average knock intensity is low, there are two groups of cycles. The first comprises of non-knocking to slightly knocking ones. The other contains cycles with relatively high knock intensity. The sudden emergence of two groups is responsible for the observed trends of SDAPP. At high overall knock intensities the first group is absent.

The objective of this work is to make a detailed investigation on the effect of using water diesel emulsions in a direct injection diesel engine. A single cylinder diesel engine was tested under variable load conditions at a constant speed of 1500 rpm at different water to diesel ratios of 0.3, 0.4, 0.5 & 0.6:1 by weight. Performance, combustion and emissions parameters were analysed and compared with pure diesel operation. Significant reductions in smoke density, NO concentraion and an improvement in brake thermal efficiency at high loads were achieved. Smoke level dropped from 3.7 BSU to 1.9 BSU and NO level dropped from 752 ppm to 463 ppm with a water to diesel ratio of 0.5:1, near full load. Water to diesel ratios of 0.4 to 0.5:1 were found to the optimal. Ignition delay, peak pressure, maximum rate of pressure rise, peak heat release rate and premixed burn fraction were higher as compared to diesel operation. Water diesel emulsions had an adverse effect on HC and CO emissions.

Experiments were conducted on a single cylinder, natural gas fuelled spark ignition engine. Air fuel ratio was varied from about stoichiometric to the lean limit at two different throttle positions with optimum spark timing. Subsequently the engine was tested at constant throttle and equivalence ratio with variable spark timing. COV (coefficient of variation) of IMEP (indicated mean effective pressure) and peak pressure increase with a reduction in equivalence ratio. When the engine starts to misfire there is a drastic increase in the COV of IMEP. Spark timing has a smaller effect on COV of IMEP than on COV of peak pressure. When the spark timing is advanced, COV of peak pressure attains a minimum value just before knock sets in. Prior cycle effects were seen when there was misfire. Spark timing had little influence on the frequency distribution of IMEPs of cycles, which was generally symmetrical about the mean.