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Owing to a high power-to-weight ratio, mini internal combustion engine is used in propelling an unmanned air vehicle. In comparison to the performance characteristics, the investigations on the combustion aspects of mini engines are scanty. This investigation concerns study of the combustion process of a mini engine and its variability. For this purpose, the experimental cylinder pressure histories were obtained on a laboratory set-up of a 7.45 cm3 capacity mini engine. The analyses of experimental data at different throttle settings reveal that there existed a varied range of rich and lean misfiring limits around a reference equivalence ratio that corresponds to the respective maximum indicated mean effective pressure. At the limiting equivalence ratios, cylinder pressure measurements showed a high degree of cycle-to-cycle variations. In some cases, a slow combustion or misfiring event preceded a rapid combustion.

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.

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.

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.

Single-cylinder engines in mass production are generally not turbocharged due to the pulsated and intermittent exhaust gas flow into the turbocharger and the phase lag between the intake and exhaust stroke. The present work proposes a novel approach of decoupling the turbine and the compressor and coupling them separately to the engine to address these limitations. An impulse turbine is chosen for this application to extract energy during the pulsated exhaust flow. Commercially available AVL BOOST software was used to estimate the overall engine performance improvement of the proposed novel approach compared to the base naturally aspirated (NA) engine. Two different impulse turbine layouts were analyzed, one without an exhaust plenum and the second layout having an exhaust plenum before the power turbine. The merits and limitations of both layouts are compared in the present study.

A diesel engine was operated with karanja oil, bio-diesel obtained from karanja oil (BDK) and diesel as pilot fuels while LPG was used as primary fuel. LPG supply was varied from zero to the maximum value that the engine could tolerate. The engine output was kept at different constant levels of 25%, 50%, 75% and 100% of full load. The thermal efficiency improved at high loads. Smoke level was reduced drastically at all loads. CO and HC levels were reduced at full load. There was a slight increase in the NO level. Combustion parameters indicated an increase in the ignition delay. Peak pressure and rate of pressure rise were not unfavorably affected. There was an increase in the peak heat release rate with LPG induction. The amount of LPG that could be tolerated with out knock at full load was 49%, 53% and 61% on energy basis with karanja oil, BDK and diesel as pilots.

This experimental study was aimed at improving a two-stroke S.I engine by injecting gasoline with air assistance through the cylinder barrel. Experimentally obtained performance and emission parameters of the engine at 25% and 100% throttle positions were analyzed at 3000 rpm. The timing of air assisted injection was optimized at 25% throttle and 3000 rpm. The performance and emissions of the engine were compared with those obtained with an optimized manifold injection system. In all cases the best spark timing was used. At 25% throttle although the thermal efficiency was increased only slightly, there was a significant reduction in HC emissions to 6.63 g/kW-h with cylinder barrel injection from 10.69 g/kW-h with manifold injection due to reduced short circuiting of the fuel. There was a reduction in NO emissions as well with cylinder barrel injection. Comparisons were made at the point of highest thermal efficiency at 100% throttle also.

In a dual fuel engine a primary fuel that is generally a gas is mixed with air, compressed and ignited by a small pilot- spray of diesel as in a diesel engine. Dual fuel engines generally suffer from the problem of lower brake power and lower peak engine cylinder pressure due to lower volumetric efficiency, although an improvement in brake specific energy consumption is observed compared to pure diesel mode. Results indicate that with an increase in percentage of CNG substitution the brake power decreases. The exhaust gas temperature and peak cylinder pressure also decrease. The rate of pressure rise is higher at lower engine speeds (1100, 1400 rev/min), although at 1700 and 2000 rev/min it is lower. The delay period throughout the engine speed shows an increasing trend. The coefficient of variation is also higher throughout the engine speeds and shows an increasing trend. The brake specific energy consumption is lower at 1100, 1400 and 1700 rev/min and at 2000 rev/min it is higher.

The increasing use of natural gas as a vehicle fuel has generated considerable research activity to characterize the performance of engines utilizing this fuel. A light duty prechamber diesel engine was run under naturally aspirated and turbocharged CNG- Diesel dual fuel mode at four engine speeds 1100, 1400, 1700 and 2000 rpm. The maximum percentage of CNG substitution continues up to the engine knock limited power. The experimental results indicate a fall in brake power under naturally aspirated CNG-Diesel dual fuel mode compared to neat diesel operation. It was due to decrease in volumetric efficiency and slower combustion. Although turbocharged dual fuel operation shows an increase in brake power as well as an improvement in brake specific energy consumption as it provides a better air/fuel mixing and improves the homogeneous natural gas/air charge.

In many Asian countries a significant automobile market share is held by two and three wheelers. Generally, cost and simplicity considerations limit the performance and emission levels of small engines. Methanol is an excellent alternative fuel for SI engines due to its high-octane number, high flame speed, presence of oxygen in its molecule and thus can be used to enhance the performance of small engines. However, use of neat methanol in SI engines poses constraints due to low energy density and poor vaporization characteristics. Also, the effectiveness of methanol as a fuel has still to be thoroughly investigated in small-bore SI engines in order to assess its potential. In this work, a small-bore 200cc three-wheeler automotive engine was modified to operate in the port fuel injection mode with neat methanol as the fuel.

In this work methanol was port injected while diesel was injected using a common rail system in a single cylinder non-road CI engine. Experiments were conducted with single (SPI) and double (DPI - pilot and main) injection of the directly injected diesel at 75% load and at a constant speed of 1500 rpm. The effects of methanol to diesel energy share (MDES) and injection scheduling on combustion stability, efficiency and emissions were evaluated. Initially, in the SPI mode, the methanol to diesel Energy Share (MDES) was varied, while the injection timing of diesel was always fixed for best brake thermal efficiency (BTE). Increase in the MDES resulted in a reduction in NOx and smoke emissions because of the high latent heat of vaporization of methanol and the oxygen available. Enhanced premixed combustion led to a raise in brake thermal efficiency (BTE). Coefficient of variation of IMEP, peak pressure and BTE were deteriorated which limited the usable MDES to 43%.

The property of methanol to surface ignite can be exploited to use it in a diesel engine even though its cetane number is very low. Poor lubricity of methanol is still an issue and special additives are needed in order to safeguard the injection system components. In this work a common rail three cylinder, turbocharged diesel engine was run in the glow plug based hot surface ignition mode under different injection strategies with methanol as the main fuel in a blend with n-butanol. n-Butanol was used mainly to enhance the viscosity and lubricity of the blend. The focus was on the effect of different injection strategies. Initially three blends with methanol to n-butanol mass ratios of 60:40, 70:30 and 80:20 were evaluated experimentally with single pulse fuel injection. Subsequently the selected blend of 70:30 was injected as two pulses (with almost equal mass shares) with the gap between them and their timing being varied.

Methanol has a very low cetane number but it can be used in the neat form in a glow plug based hot surface ignition (HSI) engine at CI engine compression ratios. A CFD simulation model of a glow plug assisted methanol HSI engine was developed and validated using experimental data reported in literature. A study on the effect of single and multipulse injection of methanol, glow plug surface temperature, injection pressure and effect of shielding it were conducted by applying the model on to a three cylinder neat methanol HSI engine. A glow surface temperature of 1273 K was found to be sufficient for ignition of methanol at 50% load while the distance between the glow plug and the injector affected the ignition delay. The sprays were ignited sequentially starting from the one closest the glow plug which resulted in extended combustion. Injecting methanol in double pulses reduced the Maximum Rate of Pressure Rise (MRPR).

Experiments were conducted to assess the relative effects of swirl (by using a masked intake valve and by providing swirl grooves on the piston crown) and squish on the performance, emission and combustion characteristics of a lean burn engine operating on liquefied petroleum gas (LPG) at a compression ratio of 10.5 under 20% and 100% throttle opening conditions. The swirl produced by the masked intake valve configuration at 100% throttle opening resulted in improved thermal efficiency and reduced HC emission, cyclic variations, ignition delay & combustion duration as compared to swirl groove piston and enhanced squish piston. The lean misfire limit was extended and there was no increase in the NO level at any given power output. At 20% throttle with high squish, under lean mixture conditions, combustion is even better than the masked valve configuration.

Gasoline direct-injection (GDI) engines have evolved as a solution to meet the current demands of the automotive industry. Benefits of a GDI engine include good fuel economy, good transient response, and low cold start emissions. However, they suffer from problems, like combustion instability, misfire, and impingement of fuel on in-cylinder surfaces. Therefore, to highlight the influence of fuel injection timing on in-cylinder flow, turbulence, mixture distribution and wall impingement, a computational study is conducted on a small-bore GDI engine. Results showed that air motion inside the engine cylinder is influenced by direct-injection of fuel, with considerable variation in turbulent kinetic energy at the time of injection. Due to charge cooling effect, mixture density and trapped mass were increased by about 10.8% and 9.5%, respectively.

In this experimental work, the potential advantages of lowering the Compression Ratio (CR) of a diesel engine in terms of performance, combustion and emission related parameters along with the analysis and improvement in its cold starting characteristics are presented. The CR of a single cylinder direct injection common rail diesel engine used for light-duty automotive applications was lowered from 18:1 to 14:1 by suitable modifications to the combustion bowl while retaining its shape. The engine with both the CRs was tested on a dynamometer rig under similar operating and fuelling conditions. Additionally, experiments were carried out to determine the extent to which in-cylinder smoke emissions can be reduced when the Nitric Oxide (NO) levels of 14 CR are matched to the higher levels seen in 18CR. In order to evaluate cold start ability and idling stability of the engine with a reduced CR (14:1), the engine was instrumented inside a cold chamber.

Gasoline Controlled Auto-Ignition (GCAI) combustion, which can be categorized under Homogeneous Charge Compression Ignition (HCCI), is a low-temperature combustion process with promising benefits such as ultra-low cylinder-out NOx emissions and reduced brake-specific fuel consumption, which are the critical parameters in any modern engine. Since this technology is based on uncontrolled auto-ignition of a premixed charge, it is very sensitive to any change in boundary conditions during engine operation. Adopting real time valve timing and fuel-injection strategies can enable improved control over GCAI combustion. This work discusses the outcome of collaborative experimental research by the partnering institutes in this direction. Experiments were performed in a single cylinder GCAI engine with variable valve timing and Gasoline Direct Injection (GDI) at constant indicated mean effective pressure (IMEP). In the first phase intake and exhaust valve timing sweeps were investigated.

In this experimental work the effect of double injection of diesel in a biogas-diesel partially premixed charge compression ignition (BDPPCCI) engine was studied. Biogas was inducted along with air while diesel was injected through a common rail system using an open electronic control unit. Experiments were done at a fixed brake mean effective pressure of 2 bar and an intake charge temperature of 40°C. The effect of start of injection (SOI) of first and second injection pulses and also the biogas energy share (BGES) were evaluated. Experiments were also done in the BDPPCCI mode with diesel being injected in a single pulse and in the biogas-diesel dual fuel (BDDF) mode for comparison. The thermal efficiency in the BDPPCCI mode was better with double injection of diesel as compared to single pulse injection due to better combustion phasing. Improved charge homogeneity and reduced wall wetting of diesel lowered the smoke emission levels with split injection.

Experiments were conducted on a turbocharged three cylinder automotive common rail diesel engine with port injection of butanol. This dual fuel engine was run with neat butanol and blends of water and butanol (up to 20% water by mass). Experiments were performed at a constant speed of 1800 rpm and a brake mean effective pressure of 11.8 bar (full load) at varying butanol to diesel energy share values while diesel was either injected as a single pulse or as twin pulses (Main plus Post). Open engine controllers were used for varying the injection parameters of diesel and butanol. Water butanol blends improved the brake thermal efficiency by a small extent because of better combustion phasing as compared to butanol without water. When the butanol to diesel energy share was high, auto-ignition of butanol occurred before the injection of diesel. This lowered the ignition delay of diesel and hence elevated the smoke level.

Direct injection of fuel has been seen as a potential method to reduce fuel short circuiting in two stroke engines. However, most work has been on low pressure injection. In this work, which employed high pressure direct injection in a small two stroke engine (2S-GDI), a detailed study of injection parameters affecting performance and combustion has been presented based on experiments for evaluating its potential. Influences of injection pressure (IP), injection timing (end of injection - EOI) and location of the spark plug at different operating conditions in a 199.3 cm3 automotive two stroke engine using a real time open engine controller were studied. Experiments were conducted at different throttle positions and equivalence ratios at a speed of 3000 rpm with various sets of injection parameters and spark plug locations. The same engine was also run in the manifold injection (2S-MI) mode under similar conditions for comparison.