A Ramesh

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.

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.

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.

Single-cylinder diesel engines are generally not turbocharged because of highly pulsating exhaust gas flow, resulting in increased speed fluctuations and reduced turbine performance. In the present work, a novel and simple method is proposed wherein an exhaust plenum is placed before the turbine to reduce the flow fluctuations. A production light-duty naturally aspirated (NA) diesel engine modified into the turbocharged version was incorporated with an exhaust plenum. Steady-state experiments were performed with the base naturally aspirated engine, the turbocharged version without an exhaust plenum (conventional pulse turbocharging), and the turbocharged version with the exhaust plenum. The present work attempts to establish the limitations of conventional pulse turbocharging in a single-cylinder diesel engine unavailable in the existing literature. Though the conventional pulse turbocharged version could deliver a boost pressure of about 2 bar (absolute), a brake power reduction of 40% and the associated drop in brake mean effective pressure was observed compared to the base NA engine due to high exhaust back pressures. The pumping work was four times higher in conventional pulse turbocharging than the NA engine, thus reducing the performance. After validating the simulation models, a one-dimensional simulation tool was used to evaluate the effect of incorporating exhaust plenum before the turbine. Simulated results predicted the brake power output within a 3% error for the NA and plenum turbocharging configurations. An optimal plenum volume was arrived at using the validated simulation model. Subsequent experiments on the turbocharged engine with the plenum in place showed a significant improvement in the engine performance and reduced exhaust emissions compared to the NA version. Brake power output was enhanced by 25%, which indicated improved thermal efficiency of 2%. Compared to the NA version, the soot, carbon monoxide (CO) and unburned hydrocarbon HC emissions were reduced by 93%, 88%, and 53%, respectively. However, an increase in oxides of nitrogen (NOx) emissions was seen, which can be controlled with suitable mitigation methods taking advantage of the significantly lower soot levels. Thus, the proposed method of placing an exhaust plenum before the turbine makes turbocharging viable on single-cylinder diesel engines with performance improvement and emission reduction when suitable NOx mitigation measures are adopted.

In order to comply with the stringent future emission mandates of automotive diesel engines it is essential to deploy a suitable combination of after treatment devices like diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and DeNox converter (Lean NOx Trap (LNT) or Selective Catalytic reduction (SCR) system). Since arriving at a suitable strategy through experiments will involve deploying a lot of resources, development of well-tuned simulation models that can reduce time and cost is important. In the first phase of this study experiments were conducted on a single cylinder light duty diesel engine fitted with a diesel oxidation catalyst (DOC) at thirteen steady state mode points identified in the NEDC (New European Driving cycle) cycle. Inlet and exit pressures and temperatures, exhaust emission concentrations and catalyst bed temperature were measured. A one dimensional simulation model was developed in the commercial software AVL BOOST. Eight of the experimental data sets from the 13 modes were taken for fine tuning the chemical kinetic rate parameters and friction factor of the model. The prediction of the model was validated at the remaining five experimental data points keeping the kinetic and friction parameters the same. The model could predict the conversion efficiency and pressure drop across the DOC within 1.5%. The influence of the length and diameter of the DOC was studied using the model which indicated that increasing the diameter is more effective than increasing the length based on the conversion efficiency and pressure drop. It was also found that increasing the diameter will enable the reduction in the DOC volume without any sacrifice in the conversion efficiency while the pressure drop can also be reduced simultaneously. The developed model can be used to size the DOC based given the requirements of space and conversion efficiency.

It is well established that reducing the compression ratio (CR) of a diesel engine leads to a significant increase in hydrocarbon (HC) and carbon monoxide (CO) emissions, especially in cold and transient conditions. Hence, it is essential to find new strategies to reduce the HC and CO emissions of a low compression ratio (LCR) diesel engine in transient conditions. In the present work, a detailed evaluation of different warm-up technologies was conducted for their effects on transient emissions characteristics of a single-cylinder naturally aspirated LCR diesel engine. For this purpose, the engine was coupled to an instrumented transient engine dynamometer setup. A transient cycle of 160 seconds with starting, idling, speed ramp-up and load ramp-up was defined, and the engine was run in automatic mode by the dynamometer. The experiments were conducted by overnight soaking the engine at a specified temperature of 25 deg.C. In the first step, the engine was tested with the stock compression ratio of 18:1, followed by the LCR configuration with the reduced compression ratio of 14:1. The results obtained show a multi-fold increase in HC and CO emissions with significant transient spikes. In the next step, the experimental investigations were continued in the LCR engine with different warm-up technologies viz., double glow plug (DGP), supercharger (SC), split cooling system (SCS) and secondary exhaust valve opening (SEVO). The transient emission characteristics of different technologies were compared with the baseline tests with the stock compression ratio, and the observed trends were analyzed. It was observed that the double glow plug approach is not very beneficial in containing the cold emissions as the HC and CO emissions of the LCR engine could be reduced only by 20 #x00025;. The split cooling system and SEVO approach were effective as they could mitigate the HC and CO emissions by 40 to 50 #x00025;. The introduction of a supercharger was the best approach to mitigate the cold and transient emissions of the LCR engine since it could reduce the HC and CO by more than 80#x00025;. Overall, the present study provides a relative comparison of different warm-up technologies in containing the transient emissions.

Supercharging a single-cylinder diesel engine has proved to be a viable methodology to reduce engine-out emissions and increase full-load torque and power. The increased air availability of the supercharger (SC) system helps to inject more fuel quantity that can improve the engine's full-load brake mean effective pressure (BMEP) without elevating soot emissions. However, the increased inlet temperature of the boosted air and the availability of excess oxygen can pose significant challenges to contain oxides of nitrogen (NOx) emissions. Hence, it is important to investigate the potential NOx reduction options in supercharged diesel engines. In the present work, the potential of low-pressure exhaust gas recirculation (LP EGR) was evaluated in a single-cylinder supercharged diesel engine for its benefits in NOx emission reduction and impact on other criteria emissions and brake specific fuel consumption (BSFC). A mass-production single-cylinder diesel engine was used for the present work after reducing its compression ratio (CR) from 18:1 to 14:1 that was needed to contain the peak firing pressure (PFP) with the SC setup. The experimental investigations revealed that the migration from the stock naturally aspirated (NA) intake system to the supercharged system resulted in a considerable increase in NOx emissions across the loads. Hence, LP EGR was introduced in the engine by an additional circuit that connected the diesel particulate filter (DPF) to the inlet port of the supercharger. An electric valve was used to control the mass flow rate of the EGR. The results concluded that the introduction of LP EGR and increased EGR rates up to 20#x00025; could reduce the NOx emissions by 52#x00025; at a reference operating point of 2000 rpm, 40 N-m. Moreover, the benefits could be obtained without any penalty on BSFC. On the contrary, in the SC system without LP EGR, for the same level of NOx reduction, the main injection timing had to be retarded significantly, resulting in a 5 #x00025; penalty on BSFC. Thus, the LP EGR system was highly beneficial in supercharged diesel engines to reduce engine-out NOx emissions without elevating the BSFC results.

The present work proposes a viable approach to develop single-cylinder diesel engines for the future by implementing regulated intake air boosting (RIAB) and engine downspeeding (ED) along with the well-established low compression ratio (LCR) approach. The investigations were conducted in a mass-production light-duty single-cylinder diesel engine initially equipped with a naturally aspirated (NA) intake system. By lowering the compression ratio (CR) and implementing the intake air boosting (IAB) using a belt-driven supercharger, the maximum brake mean effective pressure (BMEP) of the engine could be increased by 50%. More importantly, the improved performance could be achieved without violating the peak firing pressure (PFP) limits. However, a significant penalty was observed in the brake-specific fuel consumption (BSFC) at low-load operating points due to the additional power consumption of the IAB system. Hence, RIAB was implemented to optimize the boost pressure with respect to engine load to simultaneously reduce the BSFC and oxides of nitrogen (NOx) and soot emissions. Further, the increased full-load performance of the engine was leveraged to implement the ED approach that could reduce the operating speeds of the engine by 37.8%. It was observed that the benefits of downspeeding a supercharged engine are significantly high due to the simultaneous reduction of the frictional losses of the base engine and the power consumption of the supercharger. Overall, by combining the above concepts and the proven LCR approach, significant benefits could be achieved in fuel economy and exhaust emissions that are quantified for the regulatory Modified Indian Drive Cycle (MIDC) using a one-dimensional tool. The obtained results show a net reduction of 77.8% and 39.5% in the soot and NOx emissions, respectively. Moreover, a significant benefit of 14.8% could be achieved in the fuel economy. Thus the proposed approach can be used to develop single-cylinder diesel engines for the future to improve vehicle performance and comply with stringent emission regulations.

Mass-production single-cylinder engines are generally not turbocharged due to pulsated exhaust flow. Hence, about one-third of the fuel chemical energy is wasted in the engine exhaust. To extract the exhaust energy and boost the single-cylinder engines, a novel supercharging with a turbo-compounding strategy is proposed in the present work, wherein an impulse turbine extracts energy from the pulsated exhaust gas flow. Employing an impulse turbine for a vehicular application, especially on a single-cylinder engine, has never been commercially attempted. Hence, the design of the impulse turbine assumes higher importance. A nozzle, designed as a stator part of the impulse turbine and placed at the exhaust port to accelerate the flow velocity, was included as part of the layout in the present work. The layout was analyzed using the commercial software AVL BOOST. Different nozzle exit diameters were considered to analyze their effect on the exhaust back pressure and engine performance. A suitable nozzle exit diameter was chosen based on simulation results. The simulated exit conditions of the nozzle were used as inputs for velocity triangle calculations. Based on these calculations, major design features of the impulse turbine, such as blade speed, nozzle exit diameter and stator exit angle, were established. The key parameters were thus designed for the impulse turbine. The designed impulse turbine resulted in about 91% impulse turbine efficiency at rated power conditions. The proposed layout with the designed impulse turbine delivered 68% higher brake power output and improved the engine efficiency by 9.36% compared to the naturally aspirated stock engine.

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 experimental investigations were conducted in a chassis dynamometer with the stock compression ratio of 18:1 followed by the reduced compression ratio of 14:1, and the results are quantified for the regulatory modified Indian drive cycle (MIDC). The results obtained show that the LCR approach led to a significant reduction of 25% and 72% in NOx and PM emissions, respectively, along with increased HC and CO emissions by 10 and 2 fold. Further, there is a fuel economy penalty of up to 11.7% during the overall cycle. The HC, CO, and fuel economy penalties are extremely high in the initial phase of the MIDC cycle when the engine is not warmed up. The HC and CO emission penalty could be contained to 96% and 54%, respectively, by optimizing the injection settings. Moreover, the fuel economy penalty could also be reduced to 3.5%. The reasons behind the investigated single-cylinder diesel engine's transient emission and fuel consumption trends operated in the MIDC cycle are discussed in detail.