A Ramesh

A method to estimate the heat release rate of a two-stroke spark ignition engine using cylinder pressure data, the measured temperature of the gases in the exhaust manifold and the mass of fuel air mixture supplied to the engine has been developed. Experiments have been conducted on a single cylinder air cooled two-stroke spark ignition engine to obtain the average pressure crank angle data and other inputs needed for the calculation. A standard scavenging model has been used to calculate the masses of the trapped fresh mixture and exhaust gas. The heat transfer and gas properties are obtained using well-known equations. Trapped exhaust gas temperature, trapped charge temperature, trapped masses and heat release rate are obtained using the developed procedure. These results are compared with the results obtained by using a simple scheme where a polytropic index of 1.35 has been assumed. It is seen that the effect of heat transfer on the heat release rate is small if the gas temperature is properly evaluated and used in the calculations.

In a biogas diesel predominantly premixed charge compression ignition (BDPPCCI) engine the effect of composition of biogas on combustion, performance and emissions was experimentally investigated. A twin cylinder automotive common rail engine with an open electronic control unit was run on one of its cylinders in this mode while the other cylinder was nonfunctional. Three biogas compositions with methane (CH4) proportions of 53–58% (as obtained from the plant), 67% and 22–25% were used at a constant engine speed of 1800 rpm. Stable engine operation in the BDPPCCI mode even with very low methane fractions was possible without adverse effects on efficiency and emissions. Reducing the methane proportion (i.e. high proportion of CO2) enabled the brake mean effective pressure (BMEP) to be extended from 4 bar to 5 bar with sufficient margin for start of injection (SOI). Lower CH4 (i.e. increased CO2 proportion) also allowed the use of retarded SOI for diesel which resulted in reduced smoke emissions. This not only improved the combustion phasing but also lowered the peak heat release rate leaving the thermal efficiency relatively unaffected. Results indicate that extremely low levels of NO and smoke can be reached in the BDPPCCI mode at the best efficiency operating condition if the biogas composition is altered based on the output.

Experimental investigations were carried out to assess the effect of using diethyl ether to improve performance & emissions of a DI diesel engine running on water-diesel emulsion. The water-diesel ratio was 0.4:1 (by weight) and diethyl ether percentages of 5, 10 & 15 by weight were tried. The optimum quantity of diethyl ether was chosen as 10% based on emissions. It was found that diethyl ether, when added to water-diesel emulsion can significantly lower NOx and smoke levels without adverse effect on brake thermal efficiency. High HC & CO levels which are problems with water-diesel emulsions, can be significantly lowered with the addition of diethyl ether particularly at high outputs. Ignition delay and maximum rate of pressure rise at full load are also reduced. Even at part load the addition of the diethyl ether can improve the performance as compared to neat water-diesel emulsion without any adverse effect on NOx emission. However, the HC and CO levels are still higher than diesel operation. In general, it is concluded that diethyl ether can be used to solve some of the problems associated with the use of water diesel emulsions in a diesel engine Copyright © 2002 SAE International.

Biogas is an environment friendly renewable fuel which is a valuable resource in the current context of increased energy requirement and sustainability. The quality or the proportion of methane in biogas can vary significantly based on the raw material and method of production. This experimental work was aimed at evaluating the influence of such variations in composition on the energy conversion efficiency and emissions of a common rail dual fuel engine under different output conditions. The effects of post and pilot injection of diesel were also studied in this mode. Biogas with methane proportions in the range 24–68% could be utilized without significant changes in efficiency and emissions till a biogas energy share (BGES) of 60% when the injection timing of diesel was suitably adjusted. Higher than normal methane concentrations (normal: 51–53%) only elevated the NO levels with little impact on efficiency. However, when low proportions of methane were used NO could be controlled effectively particularly at low BGES. Simulation studies indicated that this reduction in NO is due to the lowered in-cylinder temperature rather than the reduced concentration of oxygen as a result of increased CO2. When the proportion of methane was decreased from 68% to 24% the start of injection of diesel had to be advanced by 3 °CA (at a BGES of 60%) to compensate for the increase in ignition delay and reduction in combustion rate. With pilot injection there was a reduction in smoke emission because of improved charge homogeneity due to the split injection process. However, post injection which is generally effective in diesel engines was not advantageous in the biogas diesel dual fuel (BDDF) mode because of the diffusion combustion the post injected fuel undergoes.

Use of vegetable oils in diesel engines results in increased smoke and reduced brake thermal efficiency. Dual fuel engines can use a wide range of fuels and yet operate with low smoke emissions and high thermal efficiency. In this work, a single cylinder diesel engine was converted to use vegetable oil (Jatropha oil) as the pilot fuel and methanol as the inducted primary fuel. Tests were conducted at 1500 rev/min and full load. Different quantities of methanol and Jatropha oil were used. Results of experiments with diesel as the pilot fuel and methanol as the primary fuel were used for comparison. Brake thermal efficiency increased in the dual fuel mode when both Jatropha oil and diesel were used as pilot fuels. The maximum brake thermal efficiency was 30.6% with Jatropha oil and 32.8% with diesel. Smoke was drastically reduced from 4.4 BSU with pure Jatropha oil operation to 1.6 BSU in the dual fuel mode. Hydrocarbon and carbon monoxide emissions were higher in the dual fuel mode with both fuels. Heat release pattern in the case of neat Jatropha oil operation showed a smaller premixed combustion phase and a larger diffusion combustion phase as compared to diesel operation. These phases were not distinguishable in the dual fuel mode. Copyright © 2001 Society of Automotive Engineers, Inc.

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.

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.

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.

Use of vegetable oils in unmodified diesel engines leads to reduced thermal efficiency and increased smoke levels. In this work, experiments were conducted to evaluate the performance while using small quantities of hydrogen in a compression ignition engine primarily fuelled with a vegetable oil, namely Jatropha oil. A single cylinder water-cooled direct-injection diesel engine designed to develop a power output of 3.7 kW at 1500 rev/min was tested at its rated speed under variable load conditions, with different quantities of hydrogen being inducted. The Jatropha oil was injected into the engine in the conventional way. Results indicated an increase in the brake thermal efficiency from 27.3% to a maximum of 29.3% at 7% of hydrogen mass share at maximum power output. Smoke was reduced from 4.4 to 3.7 BSU at the best efficiency point. There was also a reduction in HC and CO emissions from 130 to 100 ppm and 0.26-0.17% by volume respectively at maximum power output. With hydrogen induction, due to high combustion rates, NO level was increased from 735 to 875 ppm at full output. Ignition delay, peak pressure and maximum rate of pressure rise were also increased in the dual fuel mode of operation. Combustion duration was reduced due to higher flame speed of hydrogen. Higher premixed combustion rate was observed with hydrogen induction. Comparison was made with diesel being used as the pilot fuel instead of vegetable oil. In the case of diesel the brake thermal efficiency was always higher. At the optimum hydrogen share of 5% by mass, the brake thermal efficiency went up from 30.3-32%. Hydrocarbon, carbon monoxide, smoke emission and ignition delay were also lower with diesel as compared to vegetable oil. Smoke level decreased from 3.9 to 2.7 BSU with diesel as pilot at the optimum hydrogen share. Peak pressure, maximum rate of pressure rise, heat release rate and NO levels were higher with diesel than Jatropha oil. On the whole, it is concluded that induction of small quantities of hydrogen can significantly enhance the performance of a vegetable (Jatropha) oil/diesel fuelled diesel engine. © 2003 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.

The homogeneous charge compression ignition (HCCI) engines emit low levels of smoke and NOx emissions. However, control of ignition, which is mainly controlled by fuel composition, the equivalence ratio and the thermodynamic state of the mixture, is a problem. In this work, acetylene was as the fuel for operating a compression ignition engine in the HCCI mode at different outputs. The results of thermal efficiency and emissions have been compared with base diesel operation in the (compression ignition) CI mode. The relatively low self ignition temperature, wide flammability limits and gaseous nature were the reasons for selecting this fuel. Charge temperature was varied from 40 to 110°C. Thermal efficiencies were almost equal to that of CI engine operation at the correct intake charge temperature. NO levels never exceeded 20 ppm and smoke levels were always lower than 0.1 BSU. HC emissions were higher and were sensitive to charge temperature and output. However, investigations are required to further extend the operating range of acetylene HCCI operation. On the whole this work demonstrates that acetylene can be considered as a HCCI engine fuel.