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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.

Short-circuiting of the fuel air mixture during scavenging is the main reason for high fuel consumption and hydrocarbon (HC) emissions in two-stroke SI engines. Though direct injection of the fuel after the closure of ports has advantages, it is costly and complex. In this work, in a 2S-SI, single cylinder, automotive engine, LPG (liquefied Petroleum Gas) was injected through the boost port to reduce short-circuiting losses. A fuel injector was located on one of the boost ports and the air alone was fed through the other transfer and boost ports for scavenging. Experiments were done at 25% and 70% throttle openings with different injection timings and optimal spark timing at 3000 rpm. Boost port injection (BPI) of LPG reduced HC emissions at all conditions as compared to LPG-MI (Manifold Injection). Particularly significant reductions were seen at high throttle conditions and rich mixtures. HC reductions with BPI were 19% and 25% as compared to LPG-MI and gasoline-MI respectively.

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.

From the energy security and environment standpoint, the biodiesel fuels derived from vegetable oils or animal fats appear to be promising alternative to fossil diesel. Although the engine experiments prove their viability, the scientific data base for characterizing biodiesel combustion is limited. Detailed studies on the characterization of biodiesel fuels and their effects on fundamental engine processes like droplet evaporation and combustion are essential. The present study evaluates the useful thermo-physical properties and droplet evaporation characteristics of biodiesel fuels. The droplet evaporation measurements are carried out using suspended droplet experiments on five biodiesel fuels of Indian origin viz. jatropha, pongamia (karanja), neem, mahua and palm. The droplet evaporation rates of these fuels are related to properties such as binary diffusivity and molecular weight, which in turn depend on their fatty acid composition.

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.

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.

Oil with high free fatty acid (FFA) content may not be an appropriate contestant for biodiesel production due to poor process yield. The high FFA content (≻1%) will cause soap formation and the separation of products will be exceedingly difficult, and as a result, it has low yield of biodiesel product. In order to increase the process yield, pretreatment setup is required. This involves additional cost and will increase overall fuel price. Hence crude vegetable oils having high FFA can be blended with diesel for effectual employment in diesel engines. In this context, Jatropha Curcas L, non-edible tree-based oil with higher FFA content, can be considered as one of the prominent blending sources for diesel. The primary objective of the present work is to analyze the effect of FFA content of crude Jatropha Curcas L oil (CJO) on performance and emission characteristics of a direct injection (DI) diesel engine.

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.

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.

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.

In-cylinder emission control methods for simultaneous reduction of oxides of nitrogen (NOx) and particulate matter (PM) are gaining attention due to stringent emission targets and the higher cost of after-treatment systems. In addition, there is a renewed interest in using carbon-neutral biodiesel due to global warming concerns with fossil diesel. The bi-directional NOx-PM trade-off is reduced to a unidirectional higher NOx emission problem with biodiesel. The effect of water injection with biodiesel with low water quantities is relatively unexplored and is attempted in this investigation to mitigate higher NOx emissions. The water concentrations are maintained at 3, 6, and 9% relative to fuel mass by varying the pulse width of a low-pressure port fuel injector. Considering the corrosive effects of water at higher concentrations, they are maintained below 10% in the present work.

Internal combustion engines play a major role in biogas-based stationary power generation applications in rural areas, and serious progress on effective utilization of bio-resources by considering engine stability is not achieved yet. In the present study, combustion characteristics and cycle-to-cycle variations (CCVs) of a spark-ignition (SI) engine fueled with gasoline, biogas, and surrogate of bio-methane are analyzed. A single-cylinder, four-stroke SI engine (with a flexible gaseous fuel system) was operated at a couple of load points (8 Nm and 11.5 Nm) with a rotational speed of 1500 rpm. CCVs are analyzed using a statistical approach considering 1000 consecutive engine cycles for each operating condition. Results at 8 Nm showed relatively higher CCVs of indicated mean effective pressure (IMEP), peak in-cylinder pressure (Pmax), and flame initiation duration (FID) for biogas compared to methane.

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.

The limitations related to the cost-effectiveness and technological feasibility of upgrading biogas to bio-methane for rural power generation applications have prompted researchers to explore alternative approaches for improving the quality of biogas fuel. This study focuses on evaluating the effect of hydrogen enrichment on combustion characteristics and cycle-to-cycle combustion variations in a single-cylinder spark ignition engine fueled with biogas (60% CH4 and 40% CO2). The engine was run at a constant operating load of 6 Nm, with a compression ratio of 10:1 and an engine speed of 1500 rpm. To establish a baseline for comparison, engine characteristics were initially assessed using pure methane fuel. Subsequently, the share of hydrogen in the biogas fuel mixture was incrementally increased on the volumetric basis from 0% to 30% and experiments were performed to study the effects of these variations on combustion behavior.

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.

Currently, alternative fuels produced from waste resources are gaining much attention to replace depleting fossil fuels. The disposal of waste plastic poses severe environmental problems across the globe. The energy embodied in waste plastics can be converted into liquid fuel by pyrolysis. The present work explores the possibility of utilizing waste plastic oil (WPO) produced from municipal plastic wastes and waste cooking oil (WCO) biodiesel produced from used cooking oil in a dual fuel reactivity-controlled compression ignition (RCCI) mode. A single-cylinder light-duty diesel engine used for agricultural water pumping applications is modified to run in RCCI through suitable intake and fuel injection systems modifications. Alternative fuel blends, viz. WPO and WCO biodiesel with 20 vol. % in gasoline and diesel is used as a port and direct-injected fuels in RCCI. The premixed ratio and direct-injected fuel timings are optimized to achieve maximum thermal efficiency.

Despite the advantages of turbocharging in improved engine performance and reduced exhaust emissions, commercial single-cylinder engines used for automotive applications remain naturally aspirated (NA) and are not generally turbocharged. This is due to the shortcomings with pulsated and intermittent exhaust gas flow into the turbine and the phase lag between the intake and exhaust stroke. In the present study, experimental investigations are initially carried out with a suitable turbocharger closely coupled to a single-cylinder diesel engine. Results indicated that the engine power dropped significantly by 40% for the turbocharged engine compared to the NA version even though the air mass flow rate was increased by at least 1.5 times with turbocharging. A novel approach of decoupling the turbine and the compressor and coupling them separately to the engine is proposed to address these limitations.

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.