A Ramesh

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.

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.

A two-degree freedom air fuel ratio controller (Model based feed forward transient plus closed loop Proportional Integral-Derivative (PID) steady state controllers) developed for controlling the air fuel ratio of the charge in a small displacement (125 CC) SI engine is presented. The feed forward controller's airflow and injector models were developed after conducting extensive experiments on the engine modified for the Port Fuel Injection (PFI) operation. A dynamic air fuel ratio model obtained (air fuel ratio changes measured using an UEGO sensor) by injecting the Pseudo Random Binary Signal (PRBS) signal in addition to base line fuel injection pulse, was used for designing the PID controller. Optimal PID gain values were identified using Nelfer-Mead optimization technique. The control algorithms were implemented and optimized using SIMULINK blocks that are run under dSPACE on the MicroAuto box hardware. The optimized control algorithms were ported on the specially designed, in-house built, low cost engine management system (EMS) developed around an 8-bit microcontroller. The spark timing was also controlled simultaneously for knock free operation. The two-degree freedom air fuel ratio controller could maintain the air fuel ratio under steady and transient conditions closely. High thermal efficiency and low HC & NOx emissions were achieved using the developed EMS. At higher speed elevated NOx emission was observed, due to the use of leaner mixture. The improvements are expected to be higher if a suitable smaller injector is used. Copyright © 2012 by ASME.

An idle speed engine model has been proposed and applied for the development of an idle speed controller for a 125 cc two wheeler spark ignition engine. The procedure uses the measured Indicated Mean Effective Pressure (IMEP) at different speeds at a constant fuel rate and throttle position obtained by varying the spark timing. At idling conditions, IMEP corresponds to the friction mean effective pressure. A retardation test was conducted to determine the moment of inertia of the engine. Using these data, a model for simulating the idle speed fluctuations, when there are unknown torque disturbances, was developed. This model was successfully applied to the development of a closed loop idle speed controller based on spark timing. The controller was then implemented on a dSPACE Micro Autobox on the actual engine. The Proportional Derivative Integral (PID) controller parameters obtained from the model were found to match fairly well with the experimental values, indicating the usefulness of the developed idle speed model. Finally, the optimized idle speed control algorithm was embedded in and successfully demonstrated with an in-house built, low cost engine management system (EMS) specifically designed for two-wheeler applications. © 2011 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.

In spark ignition engines fuelled by alcohol gasoline blends, the proportion of the two fuels has to be varied according to the operating condition. Further high amounts of alcohol cannot be blended with gasoline because the two phases can separate under certain conditions. In this work a dual injection system, wherein n-butanol and gasoline can be injected separately in any ratio has been employed in a spark ignition engine. The objective is to determine the most suitable amounts of n-butanol and gasoline to be used at different operating conditions of a four stroke spark ignition engine when these fuels are simultaneously injected into the intake manifold using this dual injection system. Experiments are conducted at different fuel ratios and throttle positions at an equivalence ratio of 1. The system results in good vaporization of the fuels even at low load conditions because the fuel jets are aligned to hit different portions of the intake valve. Results indicate that with proper selection of the fuel ratio significant reduction in HC emissions can be achieved as compared to operation on neat gasoline. Up to 60% of n-butanol could be used at 15% throttle while up to 80% could be used at 25% throttle. These proportions are higher than what have been achieved by pre-blending these fuels. The possibility of using high amounts of n-butanol reduced the tendency to knock. Hence, with the dual injection system n-butanol can be effectively used along with gasoline. © 2013 Elsevier Ltd. All rights reserved.

Nitromethane is extensively used in drag races and in glow plug unmanned aerial vehicle (UAV) engines. However, it has not been analyzed in the combustion literature enough. Nitromethane has a low stoichiometric air-fuel ratio; it can be blended with gasoline and used in larger quantities to enhance the power output of the internal combustion (IC) engines. This could find potential use in burgeoning UAV industry. The present investigation aims at experimentally determining the laminar burning speeds of nitromethane-gasoline blends at different equivalence ratios. Tests were conducted at both ambient conditions and at elevated temperatures and pressures. A constant volume combustion chamber (CVCC) was constructed and instrumented to carry out the investigation. The pressure rise in the chamber due to combustion was acquired and analyzed to determine the laminar burning speeds. The results showed that with an increase in the nitromethane concentration in gasoline, the laminar burning speeds for all the initial conditions also increased. With the rise in initial temperatures, the laminar burning speeds were observed to increase. However, a drop was observed with a rise in the initial pressures for all the blends. The obtained results for pure gasoline were compared with existing literature. A good match was observed. The investigation also aims at providing vital experimental data, which can be used for computational fluid dynamics validation studies later.

Hydrogen is a suitable alternate fuel as it can be produced from renewable sources, and also it does not emit carbon monoxide, hydrocarbons, particulates, and carbon dioxide (CO2). The homogeneous charge compression ignition (HCCI) mode is a relatively new engine combustion concept wherein a lean premixed air-fuel mixture is admitted and ignition occurs at multiple points throughout the combustion chamber by compression. The main merits of HCCI are extremely low levels of nitric oxide (NO) and smoke emissions with the potential to develop high thermal efficiency. In this work, experiments were performed on a stationary engine in three different modes of operation, namely, hydrogen-fueled HCCI (HHCCI), hydrogen diesel HCCI (HDHCCI), and neat diesel compression ignition (CI). In the HHCCI mode, thermal efficiency was better than the conventional diesel mode, and emission of NO was very low. The charge temperature had to be held at the lowest level to avoid misfire as this resulted in the best combustion phasing and thermal efficiency. When very early in-cylinder injection of diesel was also employed along with hydrogen diesel HCCI, i.e., HDHCCI mode, intake charge heating was not needed as diesel aided the ignition process. Operation in the neat diesel HCCI mode led to advanced combustion and low thermal efficiency. However, the additional use of hydrogen led to high thermal efficiencies because of proper combustion phasing (combustion occurring close to top dead center). The operating range in the HDHCCI mode was 2–4 bar of brake mean effective pressure (BMEP). Induction of hydrogen also lowered the concentration of NO, smoke, carbon monoxide (CO), and hydrocarbon (HC) emissions as compared to the diesel-based HCCI mode. On the whole, the HHCCI mode is promising in terms of thermal efficiency and low emissions. The HDHCCI operation with common rail injection enables proper combustion phasing and has potential for high thermal efficiency with low emissions. The results indicate that the engine can be operated in the CI mode at low outputs and switch over to HCCI operation with neat hydrogen along with charge heating in the low BMEP range (0.5–2.2 bar). Beyond this output, operation can be in the hydrogen diesel HCCI mode which is viable without heating the intake charge till a BMEP of 4 bar. At higher BMEPs, the engine can only be operated in the neat diesel CI mode.

SUMMARY: Simultaneous injection of n-butanol and gasoline through a new system of two injectors directing the sprays towards the back of the intake valve in a spark-ignition engine was tried in lieu of injecting a blend of these fuels through a single injector. This system avoids the problem of phase separation, which is generally faced during the use of alcohol-gasoline blends. Experiments were conducted on a spark-ignition engine with this dual injection system using a fuel ratio of 1:1 (B50S) on the mass basis. High-speed photographs indicated that the sprays from the injectors did not interfere till they reached the intake valve. Comparisons were made with pre-blended butanol-gasoline (B50) and neat (100%) gasoline at the best spark timing. All injection and spark parameters were controlled using a real time engine controller.Neat n-butanol (B100) was superior only near full throttle with improved efficiency of the engine of about 1.2% (absolute). Heat release rates were observed to be higher and more advanced with B100 at wide open throttle. However, a reverse of this trend was observed at the throttle position of 15%. NO emission was also lower by 30% with B100 at wide open throttle as compared with gasoline. However, a small increase in carbon monoxide (CO) levels was observed because of lower post combustion temperatures as compared with gasoline and B50S. Simultaneous injection reduced hydrocarbon (HC) emissions by 13% to 50% as compared with B50 (blended fuel). HC emissions with gasoline and B50S were similar. Nitric oxide (NO) emission was lower with B50S as compared with gasoline; however it was higher than B50 because of better combustion. On the whole, the developed dual injection system was superior to the conventional method of blending in terms of performance, emissions and ability to change the fuel ratio as needed. B50S is suitable at all throttle positions, whereas B100 shows benefits at full throttle conditions. © 2013 John Wiley & Sons, Ltd.

Homogeneous charge compression ignition (HCCI) engines have the potential to operate with low nitric oxide (NOx) and soot emissions. Diesel HCCI engines pose challenges related to too early combustion, high combustion rates and wall wetting of the fuel. Injecting diesel in pulses has been shown to improve combustion in these engines. In this work, diesel injected in five timed pulses has been investigated in a compression ignition (CI) engine operating in HCCI mode. The influence of varying the first, middle and last injection pulse durations alone, in sequence, while maintaining all the other injection pulse durations equal has been studied. In addition, the influence of the injection timing of the last injection pulse was also studied. A comparison of the results has been made with HCCI operation using diesel injection in a single pulse at an injection timing of 100° CA before top dead centre (TDC) and also with the conventional compression ignition mode of operation under similar outputs. The results show that, multiple pulse (MP) injection is better than injecting the fuel in a single pulse (SP) as it leads to lower emissions and higher thermal efficiency. This is because of better combustion phasing and higher heat release rates.

A binary-type exhaust gas oxygen (BEGO) sensor that is usually used to maintain the air–fuel ratio (AFR) at stoichiometric conditions in current spark ignition (SI) engines is significantly lower in cost compared with the universal exhaust gas oxygen sensor. However, it can only switch from a high state (≈0.7 V) to a low state (≈0.1 V) when the mixture goes from richer to leaner than stoichiometric conditions or vice versa. Thus, it cannot indicate the actual AFR. A novel method of estimating the AFR of an SI engine using a BEGO sensor has been demonstrated in this work for leaner than stoichiometric mixtures. Experiments were conducted on a single-cylinder, manifold-injection SI engine. The air–fuel mixture was initially kept at a richer than stoichiometric level while the engine was maintained at constant speed and throttle. The mixture was suddenly changed to a leaner than stoichiometric level. The switching time of the BEGO sensor during this operation was noted. This was repeated for different initial and final AFRs. A relationship between the switching time and change in AFR was obtained for different initial AFRs. A look-up table to determine the AFR was made and used under test conditions. The error is less than 5% in the estimated AFR. The system was also incorporated on a low-cost microcontroller-based engine management system and tested under laboratory conditions. © 2013, SAGE Publications. All rights reserved.