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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.

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.

Unsaturated methyl esters in biodiesel make it susceptible to oxidation and fuel quality degradation upon long-term storage. It is almost impossible to use biodiesel for commercial applications immediately after production. The lead time between biodiesel production and usage is generally high, causing auto-oxidation and fuel quality degradation. Hence any onsite improvement in fuel quality should be tested with aged biodiesel. To avoid the food versus fuel debate, non-edible oil feedstocks are preferable for producing biodiesel. However, biodiesel from non-edible oil sources has more unsaturated methyl ester constituents. The traditional trade-off between oxides of nitrogen (NOx) and soot emissions in conventional diesel combustion is reduced to a more severe NOx problem with biodiesel. In the present study, NOx mitigation through fuel modifications is studied for oxidized biodiesel produced from a non-edible oil, Karanja.

Emulsification of biodiesel with water aids in reducing oxides of nitrogen (NOx) and smoke emissions simultaneously whilst improving the engine performance. However, widespread commercial applications of biodiesel-water emulsions require cost-effective surfactants that result in stable emulsions to avoid the corrosive effects of water at high temperatures prevailing in the engine combustion systems. The current investigation explored the effect of adding water to biodiesel at 6 and 12% by weight. A novel, cost-effective surfactant Polyglycerol Polyricinoleate (PGPR), was used to stabilize the emulsions. A magnetic stirrer with a heating facility was utilized to prepare biodiesel-water emulsions that were stable for over five months. The experiments were carried out on a light-duty diesel engine at a constant rated speed and varying load conditions. The results obtained with the emulsions were compared with neat biodiesel as the reference fuel.

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.

Over the years, much progress has been made in automotive vehicle technology to achieve high efficiency and clean combustion. Reactivity controlled compression ignition (RCCI) is one of the most widely studied high-efficiency, clean combustion strategies. However, complex dual-fuel injection systems and associated controls, high unburned hydrocarbon (UHC), and carbon monoxide (CO) emissions limit RCCI use in practical applications. Recently, single fuel RCCI strategies are gaining more attention as the above shortcomings are effectively addressed. Homogeneous charge with direct injection (HCDI) is a single fuel RCCI strategy that results in high thermal efficiency and lower UHC and CO emissions. In HCDI, the port-injected diesel fuel vapour and air are inducted during the intake stroke and ignited with direct-injected diesel fuel near the end of the compression stroke. However, high oxides of nitrogen (NOx) make HCDI less viable for practical applications.

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.

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.

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.

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.

Adopting a low compression ratio (LCR) is a viable approach to meet the stringent emission regulations since it can simultaneously reduce the oxides of nitrogen (NOx) and particulate matter (PM) emissions. However, significant shortcomings with the LCR approach include higher unburned hydrocarbon (HC) and carbon monoxide (CO) emissions and fuel economy penalties. Further, poor combustion stability of LCR engines at cold ambient and part load conditions may worsen the transient emission characteristics, which are least explored in the literature. In the present work, the effects of implementing the low compression ratio (LCR) approach in a mass-production light-duty vehicle powered by a single-cylinder diesel engine are investigated with a major focus on transient emission characteristics.

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.

Reactivity-Controlled Compression Ignition (RCCI) is a promising low-temperature combustion (LTC) strategy to mitigate the oxides of nitrogen (NOx) and soot emissions. However, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are much higher in RCCI compared to the conventional diesel combustion (CDC). In this present work, multiple injections of the direct-injected (DI) diesel fuel are explored as a potential method to reduce the high HC and CO emissions. Although significant research works have been done in the past on RCCI combustion in different engine types, investigations on small air-cooled diesel engines are very limited. In the present work, a production light-duty air-cooled diesel engine is modified to run in RCCI, with diesel as the high-reactivity fuel and gasoline as the low-reactivity fuel. Before modifications, the engine is run in CDC with production settings. In RCCI, experiments are initially performed with single-pulse DI.

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.

Today, gasoline direct injection (GDI) engine is one of the best strategies to meet the requirement of low pollutant emissions and fuel consumption. Generally, the GDI engine operates in stratified mixture mode at part-load conditions and homogeneous mixture mode at full-load conditions. But, at part-loads, soot emissions are found to be high because of improper air-fuel mixing. To overcome the above issue, a homogenous-stratified mixture (a combination of the overall homogeneous lean mixture with a combustible mixture at the location of the spark plug) is found to be better to reduce soot emissions compared to a stratified mixture mode. It will also help reduce fuel consumption. In this study, the analysis has been done to evaluate the effect of homogeneous-stratified mixture combustion on the performance and emission characteristics of a spray-guided GDI engine under various conditions using computational fluid dynamics (CFD).

In the present work, the possibility of engine knock detection is investigated based on in-cycle speed data, which is readily available to the ECU. Experiments were conducted at 3000 rpm with wide-open throttle condition in a single-cylinder, air-cooled, port-fuel-injection spark-ignition engine at different levels of knocking. It was found that amplitude of speed oscillations increased with the knock intensity for considered window with the size of 100 crank angle degree, starting from the top dead center of compression. The proposed knock indicators based on in-cycle speed oscillations were found to be able to identify the knock-limited spark timings at different operating conditions. Results showed that the amplitude of speed oscillations, derived from in-cycle speed data with resolution of six crank angle degree, could also be used to quantify the knock. The knock frequency based on speed oscillations also showed a sharp increase at the onset of knock.

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.

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).

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.