Now showing 1 - 10 of 33
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    Investigations on a Novel Supercharging and Impulse Turbo-Compounding of a Single Cylinder Diesel Engine
    (30-08-2022)
    Ramkumar, J.
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    Krishnasamy, Anand
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    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. An optimum nozzle area ratio of 50% for the first layout was arrived, which provided better net engine performance with 53.7% higher brake power output and 5.8% higher brake thermal efficiency. The second layout fared better with a nozzle area ratio of 13% and a plenum volume of 1 litre. The second layout delivered 52.8% higher brake power output and 5.5% higher brake thermal efficiency at rated power conditions. Both supercharged configurations produced 1.8 bar (absolute) boost pressure that increased airflow rate by 33% more than the NA configuration. This would improve combustion efficiency and reduce exhaust emission congruent with any charged engine. Thus, the present novel approach with both the layouts benefitted from charging the single-cylinder diesel engine, which was otherwise difficult in conventional turbocharging.
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    Calibration and Parametric Investigations on Lean NOx Trap and Particulate Filter Models for a Light Duty Diesel Engine
    (14-04-2020)
    Bagavathy, S. Suresh
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    Krishnasamy, Anand
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    Pandian, Senthur
    To comply with the stringent future emission mandates of light-duty diesel engines, it is essential to deploy a suitable combination of emission control devices like diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and DeNOx converter (LNT or SCR). Arriving at optimum size and layout of these emission control devices for a particular engine through experiments is both time and cost-intensive. Thus, it becomes important to develop suitable well-tuned simulation models that can be helpful to optimize individual emission control devices as well as arrive at an optimal layout for achieving higher conversion efficiency at a minimal cost. Towards this objective, the present work intends to develop a one-dimensional Exhaust After Treatment Devices (EATD) model using a commercial code. The model parameters are fine-tuned based on experimental data. The EATD model is then validated with experiment data that are not used for tuning the model. Subsequently, the model was used for studying the effects of geometrical parameters of the after-treatment devices like diameter and length on the conversion efficiency and the pressure drop. The experimental investigations are done in a single-cylinder light-duty diesel engine currently used in Indian market fitted with a Lean NOx Trap (LNT), Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF). From the Indian Driving Cycle (IDC) cycle, 8 representative operating conditions were chosen and experiments were conducted at steady state at these conditions. The chemical kinetic parameters, friction loss and heat transfer coefficient of the one-dimensional model were tuned using five of the 8 experimental data sets. The remaining three data sets were used to validate the predictions with no further tuning. The model could predict the conversion efficiency, pressure drop and outlet temperature with better accuracy. The calibrated model was then used to predict the effect of geometrical parameters. The effects of varying length and diameter of the EATD were studied with this calibrated model. The results obtained show that increasing the diameter is more effective than increasing the length for enhanced conversion efficiency and reduced pressure drop across LNT. For LNT, increasing the diameter by 5% and reducing the length by 10% compared to the existing design, results in a 1% reduction in volume, an 11% increase in pressure drop with 1.6% higher conversion efficiency. For cDPF, increasing the diameter by 10% and reducing the length by 10% results in a 9% increase in volume, a 17% reduction in pressure drop with 1.5% higher conversion efficiency. Thus, the current model and methodology can be used for optimizing the size of EATD.
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    An Improved Physics-Based Combustion Modeling Approach for Control of Direct Injection Diesel Engines
    (01-07-2020)
    Samuel, Jensen
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    Cycle-by-cycle combustion prediction in real time during engine operation can serve as a vital input for operating at optimal performance conditions and for emission control. In this work, a real-time capable physics-based combustion model has been proposed for the prediction of the heat release rate in a direct injection diesel engine. The model extends the approaches proposed earlier in the literature by considering spray dynamics such as spray penetration and Sauter mean diameter in order to calculate the mass of evaporated fuel from the spray. Wall impingement of the liquid spray is predicted by considering the liquid length based on the prevailing in-cylinder conditions. These effects are considered even after the hydraulic end of injection till the last droplet of fuel impinges on the combustion chamber wall. The fuel evaporated from the wall film and its contribution to the kinetic energy of the charge are also considered. The model assumes the heat release rate to be proportional to the mass of fuel available in the vapor phase and the instantaneous turbulent kinetic energy of the charge (which depends on the kinetic energy imparted by the injector and that available in the liquid fuel). The constants of the model were tuned with limited experimental data on a turbocharged, intercooled common rail multicylinder diesel engine. The heat release rate predicted by the model was validated against experimental data at other load conditions from the same engine and from another naturally aspirated common rail diesel engine without any further tuning. The results indicated that the model can predict the heat released during different stages of diffusion combustion viz. free jet, wall jet, and after-burning with good accuracy. Since the model does not involve iterative procedures and uses conventionally available parameter inputs in the ECU, it can be used for real-time combustion control.
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    Emission and combustion analysis of a glow-plug engine fuelled with nitromethane–methanol blends
    (01-01-2020)
    Raviteja, Sammeta
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    A small quantity of Nitromethane is often added to the glow-plug engine’s fuel to enhance the power output of an engine. The present work is aimed at characterizing performance enhancement and analyzing the in-cylinder combustion parameters to understand the reasons for the improved performance of a small glow plug-assisted compression ignition engine. The experimental tests involved the measurement of in-cylinder pressure with respect to the crank position at various equivalence ratios for different nitromethane blends. The thermodynamic analysis was carried out to obtain the heat release rates and combustion durations. Results showed increased heat release rates with nitromethane addition. Emission measurements were carried out to quantify the effect of nitromethane addition on nitric oxide (NO), hydrocarbon (HC), and carbon monoxide (CO) emissions. It was observed that the HC and CO emissions drop with nitromethane addition; however, NO emissions increase drastically.
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    Experimental and computational studies on the effects of reduced fuel injection pressure and spark plug protrusion on the performance and emissions of a small-bore gasoline direct-injection engine
    (01-06-2023)
    Jose, Jubin V.
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    Application of direct injection (DI) technology in small-bore engines, the type used in two- and three-wheelers, could improve their performance significantly. It is recognised that the use of high fuel injection pressure is beneficial in large-bore engines for a good mixture preparation. However, simple systems incorporated with low-pressure DI are desirable in small-engine segment of automobiles. Further, high fuel pressures will result in excessive wall wetting when cylinder dimensions are small. Extensive studies were carried out to investigate the minimum fuel injection pressure required for homogeneous and lean modes of operation in such small bore DI engine. The effect of spark plug protrusion in the combustion chamber was also investigated under the spray-guided configuration. Comprehensive experiments and CFD simulations were performed for estimating the engine efficiency, emissions, mixture preparation characteristics, fuel spray and fuel impingement on combustion chamber walls. Results have demonstrated that engine performance and emissions did not deteriorate when fuel injection pressure was reduced from 150 to 50 bar at full load. However, at very low pressures, like 20–30 bar, THC, CO and smoke emissions increased. Fuel injection pressure did not influence the lean limit, that is, equivalence ratio of about 0.77, but influenced the thermal efficiency at lean conditions. In order to attain high efficiency, under lean conditions, a minimum fuel pressure of 80 bar was required. The spark plug protrusion that resulted in a gap of 0.75 mm with respect to the incoming fuel spray cone has given the best engine performance, while higher protrusions affected the tumble flow and led to the stratification of charge near the spark plug, which resulted in elevated CO and smoke emissions. Hence, this work highlights that relatively lower direct injection pressures are suitable in small bore engines, which will impact the development of cost effective components for such applications.
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    Parametric investigations to establish the potential of methanol based RCCI engine and comparison with the conventional dual fuel mode
    (15-01-2022)
    Panda, Kasinath
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    This experimental study explores the potential of Methanol- Diesel Reactivity Controlled Compression Ignition (RCCI) in achieving low emissions and high thermal efficiency and compares this with the conventional dual fuel mode. A single cylinder light duty common rail water-cooled diesel engine was run at a constant speed of 1500 rpm and IMEP of 5 bar (50% of rated load) with methanol being port injected. In the conventional dual fuel mode, diesel was directly injected as a single pulse and its injection timing was adjusted for maximum efficiency. The RCCI mode of combustion could only be supported with one early injection pulse followed by another late injection pulse of diesel. The methanol to diesel energy share (MDES) could be enhanced to 56% in the RCCI mode with proper setting of the injection parameters from 45% in the dual fuel mode. A higher quantity in the second diesel pulse that occurred close to TDC led to higher thermal efficiency and good combustion stability. The NO level was significantly lower in the RCCI mode by about 95% and soot emission was reduced by about 78% while the thermal efficiency was increased from 36% to 38% as compared to the dual fuel mode at a fixed MDES. Beyond an MDES of 45% heating of the intake air to about 85 °C was needed to enhance the thermal efficiency to about 42% without affecting NO emissions. Higher MDES values always reduced the soot and NO levels and but enhanced the HC and CO emissions which could be controlled by increasing the temperature of the intake air. On the whole, thermal efficiency higher than the conventional dual fuel mode along with considerably lower NO emissions and comparable soot, HC and CO emissions and enhanced methanol share can be achieved in the Methanol RCCI mode when twin pulse injection of diesel.
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    A novel strategy of extremely delayed intake valve opening to improve the cold-start characteristics of a low compression ratio diesel engine
    (01-01-2021)
    Vikraman, V.
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    Anand, K.
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    Combined in-cylinder and after-treatment emission control methods are generally adopted to meet the current stringent emission targets for diesel engines. It is well established that reducing the geometric compression ratio (CR) results in a simultaneous reduction in the oxides of nitrogen (NOx) and soot emissions in diesel engines. However, poor cold-start characteristics prevent extensive use of low compression ratio (LCR) diesel engines for automotive applications. In the present work, a novel extremely delayed intake valve opening (IVO) strategy is proposed to improve the cold-start characteristics of a light-duty LCR diesel engine. A commercial one-dimensional gas-exchange model was used to optimize the intake valve open and close timings. The results corresponding to a cranking speed of 200 rpm and ambient temperature of 0°C show that advancing the intake valve close (IVC) timing increases the effective compression stroke that can improve the cylinder temperature by 5%. Further, implementing ‘extremely delayed IVO’ by retarding the timing from 1°CA to 61°CA aTDC could help to further increase the cylinder temperature by 14% compared to the base timings. The delayed opening of the intake valve leads to a higher expansion of the cylinder mass, leading to a lower cylinder pressure before IVO and a higher intake air velocity immediately after IVO. With the higher intake air velocity, the incoming air’s kinetic energy is dissipated to increase the stagnation temperature, resulting in an overall benefit in cylinder temperature. The experimental measurements conducted in a cold chamber with the optimized IVO and IVC timings confirmed the benefits by achieving a better cold-startability of the LCR engine. In comparison, the LCR engine with the stock valve timings could be started only up to +5°C, the optimized valve timings could ensure startability up to −10°C without any starting aids. Thus, the proposed approach of adopting the optimized valve timings can help LCR diesel engines to overcome the limitations of cold-startability.
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    Publication
    Fuel Injection Strategies for Improving Performance and Reducing Emissions of a Low Compression Ratio Diesel Engine
    (21-09-2021)
    Vellandi, Vikraman
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    Krishnasamy, Anand
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    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. On the contrary, retarding the main injection timing and increasing the injection pressure at high-load operating points can further reduce the soot emissions without elevating the NOx emissions. The results obtained with optimized injection timings quantified for the Indian drive cycle show that the soot emissions of the LCR engine are further reduced from 64% to 76%. Moreover, the HC and CO emissions penalty could be reduced significantly to 76% and 54%, respectively, and the fuel consumption penalty could be brought down to 1.6%. Thus, by adopting the proposed fuel injection strategy, the emissions and fuel consumption penalty of LCR engines can be reduced significantly.
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    A physics-based model for real-time prediction of ignition delays of multi-pulse fuel injections in direct-injection diesel engines
    (01-03-2020)
    Samuel J, Jensen
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    Real-time prediction of in-cylinder combustion parameters is very important for robust combustion control in any internal combustion engine. Very little information is available in the literature for modeling the ignition delay period of multiple injections that occur in modern direct-injection diesel engines. Knowledge of the ignition delay period in diesel engines with multiple injections is of primary interest due to its impact on pressure rise during subsequent combustion, combustion noise and pollutant formation. In this work, a physics-based ignition delay prediction methodology has been proposed by suitably simplifying an approach available in the literature. The time taken by the fuel-spray tip to reach the liquid length is considered as the physical delay period of any particular injection pulse. An equation has been developed for predicting the saturation temperature at this location based on the temperature and pressure at the start of injection. Thus, iterative procedures are avoided, which makes the methodology suitable for real-time engine control. The chemical delay was modeled by assuming a global reaction mechanism while using the Arrhenius-type equation. Experiments were conducted on a fully instrumented state-of-the-art common-rail diesel engine test facility for providing inputs to develop the methodology. The thermodynamic condition before the main injection was obtained by modeling the pilot combustion phase using the Wiebe function. Thus, the ignition delays of both pilot and main injections could be predicted based on rail pressure, injection timing, injection duration, manifold pressure and temperature which are normally used as inputs to the engine control unit. When the methodology was applied to predict the ignition delays in three different common-rail diesel engines, the ignition delays of pilot and main combustion phases could be predicted within an error band of ±25, ±50 and ±80 µs, respectively, without further tuning. This method can hence be used in real-time engine controllers and hardware-in-the-loop systems.
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    Novel strategies to overcome the limitations of a low compression ratio light duty diesel engine
    (01-09-2021)
    Vikraman, V.
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    Anand, K.
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    Low compression ratio (LCR) approach in diesel engines can reduce the oxides of nitrogen (NOx) and soot emissions simultaneously owing to lower temperatures and longer fuel-air premixing time. The present work investigates the effects of lowering the geometric compression ratio (CR) from 18:1 to 14:1 in a naturally aspirated (NA) single cylinder common rail direct injection (CRDI) diesel engine. Based on the investigations done across the entire speed and load range, significant benefits were observed in the NOx and soot emissions. However, lowering the compression ratio had adverse effects on brake specific fuel consumption (BSFC), unburned hydrocarbon (HC) and carbon monoxide (CO) emissions, especially at low-load and high-speed operating points. To overcome these limitations, novel strategies including split-cooling system (SCS) and secondary exhaust valve opening (SEVO) are proposed in the present work. While the fuel injection parameters optimization specific to LCR could help to improve the BSFC, HC and CO emissions penalty to a reasonable extent, the SCS concept can provide further benefits by reducing the heat loss to coolant and improving the engine component temperatures. Increasing the residual gas fraction using the optimized SEVO concept could further improve the charge temperature leading to a further reduction in the BSFC, HC and CO emissions. The net benefits of the optimized LCR approach are quantified for the modified Indian drive cycle (MIDC) using a one-dimensional simulation tool. The results obtained show a signification reduction of 22% and 74% in NOx and soot emissions respectively as compared to the base 18 CR engine results. Moreover, the penalty in HC and CO emissions could be contained to a large extent resulting in only a slight penalty of 23% and 20% respectively. Furthermore, the higher BSFC with the LCR approach could be successfully addressed and the final values were found to be better than the stock compression ratio by 1.5%. Overall, the strategies proposed in the present work are found to be beneficial to develop modern diesel engines in compliance with the future emission regulations which demand extreme control on NOx and soot emissions.