COMPUTATIONAL ANALYSIS OF INTERCITY BUS WITH IMPROVED AESTHETICS AND AERODYNAMIC PERFORMANCE ON INDIAN ROADS

ABSTRACT For buses which covers long distances in a single stretch, improved aerodynamic design with good aesthetics attracts customers besides saving fuel consumption. Ergonomic design of interiors for increased comfort of the passengers also plays a vital role. In the present work emphasis is given on the redesign of an intercity bus with enhanced exterior styling reduced aerodynamic drag and increased comfort for the passengers. Extensive product study and market study are carried out. Existing intercity bus is benchmarked and analyzed for styling, aerodynamic performance and comfort. Fluent, a CFD code is used to evaluate the aerodynamic performance. Principles of product design are used to analyze the styling and comfort. The benchmarked high-floor bus is redesigned with low -floor for reduced aerodynamic drag. The exterior of the chosen bus is redesigned with emphasis on improvised aerodynamic performance and appealing looks. The interior was modified to meet aspirations of the commuters. The results of the redesigned exterior body showed a reduction of C d from 0.581 to 0.41 at a speed of 100 km/hr and overall aerodynamic drag reduction by about 30% due to combined effect of reduced C d and frontal area

Development of variable timing fuel injection cam for effective abatement of diesel engine emissions

Fossil fuel run diesel engines are being favored in light, medium and heavy duty applications as they exhibit higher fuel conversion efficiencies. Direct injection diesels are still facing challenges to obtain trade-off between oxides of nitrogen and particulate emissions. There are sophisticated strategies such as common rail direct injection, particulate filters with associated sensors and actuators but limited to expensive comfort vehicles. In the present experimental study, a mechanically operated simple component, variable timing fuel injection cam, is designed for a 510 cc automotive type naturally aspirated, water-cooled, direct injection diesel engine. Modifications in the fuel injection cam and gear train are carried out to suit the existing engine configuration. Variable speed tests are carried out for testing the efficacy of component on both engine and chassis dynamometers for performance and emissions. It is observed that the engine which is already retarded could further be retarded with variable timing fuel injection cam. Significant reductions in NOx and smoke emission levels are achieved. Combined effect of VIC with 7% EGR could reduce CO by about 88%, HC + NOx by 37% and PM emissions by 90%. The Engine incorporated with the designed component and EGR, successfully satisfied the existing emission norms with improved power and specific fuel consumption.DI diesel engine Emission norms Variable timing fuel injection cam EGR

Effective reduction of NOx emissions from diesel engine using split injections

Good fuel economy and high thermal efficiency of direct injection diesel engines are certainly welcome characteristics from the viewpoints of preserving energy sources and suppressing global warming. Despite the attractive fuel economy, high emissions of oxides of nitrogen (NOx) and particulate matter (PM) with their unresolved trade-off are a major challenge to be addressed by researchers. Downsizing of the engine, dilution using exhaust gases, retardation of injection timing, etc. are widely adopted techniques to lower NOx emissions. Of late, multiple/split injection strategy is garnering much attention from the researchers for its potential to effectively address NOx, soot and piston work trade-offs. The effects of variation of fuel injection timing, dilution using EGR are investigated and compared against the proposed technique of split injections (25/75 and 75/25) on a single cylinder diesel engine using numerical experiments in the present work. For this purpose, a quasi-dimensional model has been developed primarily using the derivations of first law of thermodynamics and ideal gas equation. Models predicting heat release rates, heat transfer losses, ignition delay, chemistry of combustion, NOx and soot formations are coupled to the model using phenomenological considerations. Split injection with a smaller quantity of fuel injected in the first pulse is observed to significantly lower NOx emissions due to the restrain in premixed phase of combustion of second pulse. Split injections are observed to effectively address NO-piston work trade-off compared to increasing dilution rates using EGR and retarding injection timing towards TDC. Keywords: Diesel engine, Emissions, EGR, Injection timings, NOx-piston work trade-off, Split injection

Effect of ramp-cavity on hydrogen fueled scramjet combustor

Sustained combustion and optimization of combustor are the two challenges being faced by combustion scientists working in the area of supersonic combustion. Thorough mixing, lower stagnation pressure losses, positive thrust and sustained combustion are the key issues in the field of supersonic combustion. Special fluid mechanism is required to achieve good mixing. To induce such mechanisms in supersonic inflows, the fuel injectors should be critically shaped incurring less flow losses. Present investigations are focused on the effect of fuel injection scheme on a model scramjet combustor performance. Ramps at supersonic flow generate axial vortices that help in macro-mixing of fuel with air. Interaction of shocks generated by ramps with the fuel stream generates boro-clinic torque at the air & liquid fuel interface, enhancing micro-mixing. Recirculation zones present in cavities increase the residence time of the combustible mixture. Making use of the advantageous features of both, a ramp-cavity combustor is designed. The combustor has two sections. First, constant height section consists of a backward facing step followed by ramps and cavities on both the top and bottom walls. The ramps are located alternately on top and bottom walls. The complete combustor width is utilized for the cavities. The second section of the combustor is diverging area section. This is provided to avoid thermal choking. In the present work gaseous hydrogen is considered as fuel. This study was mainly focused on the mixing characteristics of four different fuel injection locations. It was found that injecting fuel upstream of the ramp was beneficial from fuel spread point of view

Effective reduction of in-cylinder peak pressures in Homogeneous Charge Compression Ignition Engine – A computational study

HCCI mode of combustion is known for simultaneous reduction of NOx and PM emissions besides yielding low specific fuel consumption. The nature of volumetric combustion of HCCI engine leads to the development of high peak pressures inside the combustion chamber. This high peak pressures may damage the engine, limiting the HCCI engine life period and thus demands sturdy designs. In this study an attempt is made to analyze computationally the effect of induction swirl in reducing the peak pressures of a HCCI engine under various operating parameters. For the study, specifications of a single cylinder 1.6 L, reentrant piston bowl diesel engine are chosen. For the computational analysis ECFM-3Z model of STARCD is considered. This model is suitable to analyze the combustion processes in SI and CI engines. As HCCI engine is a hybrid version of SI and CI engines, ECFM-3Z model with necessary modifications is used to analyze the peak pressures inside the combustion chamber. The ECFM-3Z model for HCCI mode of combustion is validated with the existing literature to make sure that the results obtaining are accurate. Numerical experiments are performed to study the effect of compression ratio, equivalence ratio, exhaust gas recirculation and boost pressure under different swirl ratios in reducing the in-cylinder peak pressures. The results showed that swirl ratio has a considerable impact in limiting the peak pressures of HCCI engine. The analysis resulted in achieving about 21% reduction in peak pressures are achieved when a swirl ratio of 4 with 30% EGR is adopted when compared to a swirl ratio of 1 with 0% EGR. The study revealed that out of the four operating parameters selected, lower compression ratios, higher EGR concentrations, lower equivalence ratios, lower boost pressures and higher swirl ratios are favorable in reducing the peak pressures