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Setting the correct valve timing and lift based on the operating speed will be the key to achieving good volumetric efficiency and torque. Continuously variable valve timing systems are the best choice but are too expensive. In this work a novel two stage variable valve actuation system was conceived and developed for a small single cylinder three wheeler spark ignition engine. The constraints were space, cost and complexity. The developed system uses one cam for low speeds and another cam that has a higher lift and duration for high speeds. The shift between the cams occurs through the mechanism even as the engine runs by the operation of a stepper motor which can be connected to the engine controller. A one dimensional simulation model validated with experimental data was used to predict the suitable valve timings and lifts in low and high speed ranges. Two profiles were then selected.

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.

Air motion inside the engine cylinder plays a predominant role on combustion and emission processes. An attempt has been made in this investigation to simulate the in-cylinder air motion in a DI diesel engine with four different piston configurations such as dome piston, bowl on dome and pentroof piston and pentroof offset bowl piston. For computational analysis, the commercial general purpose code STAR-CD Es-ice has been used, which works on the method of finite volume. To validate the simulation, qualitative and quantitative comparisons have been done with the PIV results available in the literature. From this study, the best possible piston configuration has been arrived at.

Direct injection diesel engines are used in both light duty and heavy duty vehicles because of higher thermal efficiency compared to SI engines. However, due to only short time available for fuel-air mixing, combustion process depends on proper mixing. As a result, DI Diesel engine emits more NOx and soot into the atmosphere. Therefore, to achieve better combustion with less emission and also to accelerate the fuel-air mixing to improve the combustion, appropriate design of combustion chamber is crucial. Hence, in this work a study has been carried out using CFD to evaluate the effect of combustion chamber configuration on Diesel combustion with two different piston bowls. The two different piston configurations considered in this study are centre bowl on flat piston and pentroof offset bowl piston.

The present research explores the application of biodiesel fuel in a stationary agricultural engine operated under the Homogenous charge compression ignition (HCCI) mode. To achieve HCCI combustion, a fuel vaporizer and a high-pressure port fuel injection system are employed to facilitate rapid evaporation of the biodiesel fuel. The low volatility of biodiesel is one of the significant shortcomings, which makes it inevitable to use a fuel vaporizer at 380oC. Consequently, the charge temperature is high enough to promote advanced auto-ignition. Further, the high reactivity of biodiesel favors early auto-ignition of the charge. Besides, biodiesel exhibits a faster burn rate due to its oxygenated nature. The combined effect of advanced auto-ignition and faster burn rate resulted in a steep rise in the in-cylinder pressures, leading to abnormal combustion above 20% load. Diluting the charge reduces reactivity and intake oxygen concentration, facilitating load extension.

Simultaneous reduction of oxides of nitrogen (NOx) and smoke emissions from diesel engines has always been a challenging task. In this research work, a relative comparison of diesel-water emulsion and water vapor induction methods has been made to examine NOx and smoke emissions reduction potential of a light-duty diesel engine. The water concentration was maintained at 6% of the total fuel in the emulsion and 6% of the total incoming air mass in the fumigation method. A stable diesel-water emulsion is prepared using commercially available surfactants, Span 80 and Tween 80 at 10% concentration. The stability of the emulsion was examined by visual inspection. The droplet size was quantified using dynamic light scattering technique and the emulsion was deemed stable for approximately 105 days on storage at room temperature. To generate water vapor in the intake manifold, 20 ultrasonic atomizers are utilized.

This paper deals mainly with computer simulation of processes of Gasoline Direct Injection (GDI) associated with Extended Expansion Engine (EEE) concept applied to a four-stroke, single-cylinder SI engine. In the case of standard SI engines, part-load brake thermal efficiencies are low due to higher pumping losses. The pumping losses can be reduced by operating the engine always at full throttle as done in extended expansion engine. In extended expansion engine, higher Geometric Expansion Ratio (GER) compared to Effective Compression Ratio (ECR) is responsible for better performance at part loads. Usually, in this engine, by delaying inlet valve closure timing along with reduced clearance volume, extended expansion is achieved. Experimentally many researchers have proved that variable valve timing and variable compression ratio techniques adopted in SI engines, improves the part- load performance greatly.

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.

Today, GDI engines are becoming very popular because of better fuel economy and low exhaust emissions. The gain in fuel economy in these engines is realized only in the stratified mode of operation. In wall-guided GDI engines, the mixture stratification is realized by properly shaping the combustion chamber. However, the level of mixture stratification varies significantly with engine operating conditions. In this study, an attempt has been made to understand the effect of engine operating parameters viz., compression ratio, engine speed and inlet air pressure on the level of mixture stratification in a four-stroke wall-guided GDI engine using CFD analysis. Three compression ratios of 10.5, 11.5 and 12.5, three engine speeds of 2000, 3000 and 4000 rev/min., and three inlet air pressures of 1, 1.2 and 1.4 bar are considered for the analysis. The CONVERGE software is used to perform the CFD analysis. Simulation is done for one full cycle of the engine.

Gasoline direct injection (GDI) engines are well known for their ability to operate at the stratified fuel-air mixture, and thereby they are highly efficient than port fuel injection (PFI) engines. However, the stratification of the in-cylinder mixture leads to higher nitrogen oxides (NOx) and soot emissions with lower hydrocarbon (HC) emissions. The PFI works under a homogeneous mixture, which leads to lower NOx and soot emissions with compensation of HC emissions. By combining the advantages of GDI and PFI modes, it is possible to achieve higher fuel efficiency with lower emissions. Therefore, in the present study, four different injection strategies, namely, pure GDI, gasoline-direct multiple-injection (GDMI), combined GDI with PFI (GDI-PFI), and pure PFI are investigated under various load conditions using computational fluid dynamics (CFD) analysis. The effect of these strategies on mixture formation, indicated mean effective pressure (IMEP), and emissions are evaluated.

This paper deals with experimental study of in-cylinder tumble flows in a single-cylinder, four-stroke, two-valve internal combustion engine using a pentroof-offset-bowl piston under non-reacting conditions with four intake manifold orientations at an engine speed of 1000 rev/min., during suction and compression strokes using particle image velocimetry. Two-dimensional in-cylinder tumble flow measurements and analysis are carried out in combustion space on a vertical plane passing through cylinder axis. Ensemble average velocity vectors are used to analyze the tumble flows. Tumble ratio (TR) and average turbulent kinetic energy (TKE) are evaluated and used to characterize the tumble flows. From analysis of results, it is found that at end of compression stroke, 90° intake manifold orientation shows an improvement in TR and TKE compared other intake manifold orientations considered.

Mixture distribution in the combustion chamber of gasoline direct injection (GDI) engines significantly affects combustion, performance and emission characteristics. The mixture distribution in the engine cylinder, in turn, depends on many parameters viz., fuel injector hole diameter and orientation, fuel injection pressure, the start of fuel injection, in-cylinder fluid dynamics etc. In these engines, the mixture distribution is broadly classified as homogeneous and stratified. However, with currently available engine parameters, it is difficult to objectively classify the type of mixture distribution. In this study, an attempt is made to objectively classify the mixture distribution in GDI engines using a parameter called the “stratification index”. The analysis is carried out on a four-stroke wall-guided GDI engine using computational fluid dynamics (CFD).

Preparation of air-fuel mixture and its stratification, plays the key role to determine the combustion and emission characteristics in a gasoline direct injection (GDI) engine working in stratified conditions. The mixture stratification is mainly influenced by the in-cylinder flow structure, which mainly relies upon engine geometry i.e. cylinder head, intake port configuration, piston profile etc. Hence in the present analysis, authors have attempted to comprehend the effect of cylinder head geometry on the mixture stratification, combustion and emission characteristics of a GDI engine. The computational fluid dynamics (CFD) analysis is carried out on a single-cylinder, naturally-aspirated four-stroke GDI engine having a pentroof shaped cylinder head. The analysis is carried out at four pentroof angles (PA) viz., 80 (base case), 140, 200 and 250 with the axis of the cylinder.

The presence of unsaturated methyl esters in biodiesel makes it susceptible to oxidation and fuel quality degradation upon long-term storage. In the present work, the effects of oxidation of Karanja biodiesel upon long-term storage on the combustion and emission characteristics of a heavy-duty truck diesel engine are studied. The Karanja biodiesel is stored for one year in a 200 litres steel barrel at room conditions to mimic commercial storage conditions. The results obtained show that compared to diesel, the start of injection of fresh and aged biodiesels are advanced by ~2-degree crank angle, and the ignition delay time is reduced. Aged biodiesel showed a slightly smaller ignition delay compares to fresh biodiesel. The fuel injection and combustion characteristics of fresh and aged biodiesels were similar at all the load conditions. Both fresh and aged biodiesels produced higher oxides of nitrogen (NOx) and lower smoke emissions compared to diesel.

For controlling oxides of nitrogen (NOx) and particular matter (PM) emissions from diesel engines, various fuel and combustion mode modification strategies are investigated in the past. Low temperature combustion (LTC) is an alternative combustion strategy that reduces NOx and PM emissions through premixed lean combustion. Dual fuel reactivity-controlled compression ignition (RCCI) is a promising LTC strategy with better control over the start and end of combustion because of reactivity and equivalence ratio stratification. However, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are significantly higher in RCCI, especially at part-load conditions. The present work intends to address this shortcoming by utilizing oxygenated alternative fuels. Considering the limited availability and higher cost, replacing conventional fuels completely with alternative fuels is not feasible.

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.

The present work investigates the effects of lowering the compression ratio (LCR) from 18:1 to 14:1 and optimizing the fuel injection parameters across the operating range of a mass production light-duty diesel engine. The results were quantified for a regulatory Indian drive cycle using a one-dimensional simulation tool. The results show that the LCR approach can simultaneously reduce the oxides of nitrogen (NOx) and soot emissions by 28% and 64%, respectively. However, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions increased significantly by 305% and 119%, respectively, with a 4.5% penalty in brake specific fuel consumption (BSFC). Hence, optimization of fuel injection parameters specific to LCR operation was attempted. It was evident that advancing the main injection timing and reducing the injection pressure at low-load operating points can significantly help to reduce BSFC, HC and CO emissions with a slight increase in the NOx emissions.

Ammonia is one of the most promising zero carbon fuels for meeting carbon neutrality targets and zero carbon emissions. Ammonia has gained a lot of research interest recently as a hydrogen energy carrier, and direct use of ammonia as a fuel in engines will aid the transformation toward sustainable energy future. In this work, the effect of ammonia shares on combustion and performance characteristics of methane-fueled SI engine is evaluated by increasing the ammonia share by small fractions (0 to 30% by volume) in the fuel mixture (CH4/NH3 blend). Experiments were performed at constant engine load of 8 Nm (BMEP of 1.52 bar), while maintaining constant engine speed (1500 rpm), stoichiometric operation (λ = 1), and optimum spark advance for MBT conditions.

This paper deals with in-cylinder flow field analysis in a motored two-stroke engine by CFD technique using STAR-CD. The main aim of this study is to find out the best turbulence model which predicts the fluid flow field inside the cylinder of a two-stroke engine. In this study, a single-cylinder, two-stroke engine which is very commonly used for two-wheeler application in India is considered. Entire analysis is done at an engine speed of 1500 rev/min. under motoring conditions. Here, three commonly used turbulence models viz. standard k-ε, Chen k-ε and RNG k-ε are considered. In addition, experiments were also conducted on the above engine at the motoring conditions to measure velocity vectors of in-cylinder flow fields using particle image velocimetry (PIV). The results of PIV were also used for validating the CFD predictions.

This paper deals with a numerical investigation on swirl generation by a helical intake port and its effects on in-cylinder flow characteristics with axisymmetric piston bowls in a small four-valve direct injection diesel engine. The novelty of this study is in determining the appropriate design and orientation of the helical port to generate high swirl. A commercial CFD software STAR-CD is used to perform the detailed three dimensional simulations. Preliminary studies were carried out at steady state conditions with the helical port which demonstrated a good swirl potential and the CFD predictions were found to have reasonably good agreement with the experimental data taken from literature. For transient cold flow simulations, the STAR-CD code was validated with Laser Doppler Velocimetry (LDV) experimental velocity components’ measurements available in literature.