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A robust and cost-effective off-road engine that is economical for backhoe application is developed to meet the Indian BS-III CEV (construction equipment vehicle) standards equivalent to the US Tier-3 emissions regulation for markets where (a) advanced maintenance facilities are not available in remote areas of operation, (b) availability of the right fuel is not fully assured, (c) the initial cost of the engine is under tight control and (d) the legendary fuel economy of direct-injection diesel engines is not traded off when migrating to higher emissions standards. The highlights of the layout of the 4-cylinder 3.8-liter 56 kW diesel engine are the use of a high-pressure exhaust gas recirculation (EGR) and a proven inline mechanical fuel injection equipment that is easy to maintain and tolerant to inferior quality of fuels used inadvertently in remote areas of operation. Use of 25% EGR reduces oxides of nitrogen (NOx) formation inside the combustion chamber by 30%.

The absorption and desorption of fuel by cylinder lubricating oil films has been modelled using principles of mass transfer. Henry's Law for a dilute solution of fuel in oil is used to relate gas to liquid phase fuel concentrations. Mass transfer conductances in gas and liquid phases are considered, the former via use of Reynold's Analogy to engine heat transfer data, the latter through assuming molecular diffusion through an effective penetration depth of the oil film. Oxidation of desorbed fuel is assumed complete if the mean of burned gas and lubricating oil film temperatures is greater than 1100K,. Below this value the desorbed fuel is considered to contribute to hydrocarbon emissions. Comparison with engine test data corroborate the absorption/desorption hypothesis. The model indicates the equal importance of gas and liquid phase conductances.

To uprate a 6-Cylinder In-line engine from 123 kW to 165 kW in power and upgrade the emission from Euro-2 to Euro-3 it was required to go for higher peak-firing pressures (PFP). The capability of Engine's Crankshaft to withstand the PFP was increased from 125 bar to 150 bar, maintaining the same cylinder centre distance. A crank-train model was used to achieve the required crankshaft strength for infinite fatigue life. The three aspects of crankshaft design, namely, crank strength, bearing selection, journal-pin lubrication and torsional vibration were considered during the design stage. The strength to withstand 150 bar PFP was achieved by increasing the crank web-thickness. To maintain the same cylinder centre distance, crankpin and main-journal lengths were reduced. Increased throw stiffness was achieved by increasing the crankpin diameter to improve crankshaft torsional behaviour.

Emission norms are introduced to limit exhaust pollutants from vehicular engines to improve and control ambient air quality. Thermodynamic simulation results showed the possibility of upgradation from Euro-2 to Euro-3 emission norms using a low pressure inline fuel injection pump. Geometric parameters of piston bowl, injection nozzle were adjusted and the combustion parameters like swirl start of injection, controlled injection and jet penetration were fine tuned to achieve the emission norms using the cost effective inline fuel injection pump. This fuel injection system is tolerant to indifferent fuel quality as it is lubricated by engine oil and the clearances within the pump do not demand exceptional lubricity or cleanliness of the fuel. The exhaust is polished off soluble organic fractions, carbon monoxide and hydrocarbons using a lightly loaded diesel oxidation catalyst that is tolerant to 500 ppm sulphur in fuel. Data from 20 engines showed emission is consistent.

Estimation of the ignition delay and concentration of exhaust emissions carries great importance in engine development process. In direct injection (DI) diesel engines, ignition delay has direct effect on startability, noise and pollutant formation. Hydrocarbon (HC) emissions are mainly due to the unburnt or partially burnt fuel leaving the engine exhaust system. In the present work, correlations have been developed for ignition delay and HC emissions. Satisfactory comparison of predicted and experimental values of ignition delay and HC emission under different operating conditions for various engines, widely varying in dimensions, method of aspiration and rated speeds validated the correlations. These correlations are useful as design tools for engine development.

It is desirable for engines to produce high torque in lower speed ranges. Such conditions are encountered when vehicles climb gradients. Two techniques are compared in this paper along with their merits and demerits to improve torque of a CI engine for lower speeds. The first method increases swirl at lower speed whereas the second method uses a combined charging system to improve airflow rates. Matching of Turbocharging equipment with diesel engine throughout the operating speed range has also been discussed in this paper. Combining both methods, provides excellent torque characteristics at lower speeds without increase in smoke and other emissions. This improves driveability of the vehicles.