A Ramesh

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.

This experimental study explores the potential of Methanol- Diesel Reactivity Controlled Compression Ignition (RCCI) in achieving low emissions and high thermal efficiency and compares this with the conventional dual fuel mode. A single cylinder light duty common rail water-cooled diesel engine was run at a constant speed of 1500 rpm and IMEP of 5 bar (50% of rated load) with methanol being port injected. In the conventional dual fuel mode, diesel was directly injected as a single pulse and its injection timing was adjusted for maximum efficiency. The RCCI mode of combustion could only be supported with one early injection pulse followed by another late injection pulse of diesel. The methanol to diesel energy share (MDES) could be enhanced to 56% in the RCCI mode with proper setting of the injection parameters from 45% in the dual fuel mode. A higher quantity in the second diesel pulse that occurred close to TDC led to higher thermal efficiency and good combustion stability. The NO level was significantly lower in the RCCI mode by about 95% and soot emission was reduced by about 78% while the thermal efficiency was increased from 36% to 38% as compared to the dual fuel mode at a fixed MDES. Beyond an MDES of 45% heating of the intake air to about 85 °C was needed to enhance the thermal efficiency to about 42% without affecting NO emissions. Higher MDES values always reduced the soot and NO levels and but enhanced the HC and CO emissions which could be controlled by increasing the temperature of the intake air. On the whole, thermal efficiency higher than the conventional dual fuel mode along with considerably lower NO emissions and comparable soot, HC and CO emissions and enhanced methanol share can be achieved in the Methanol RCCI mode when twin pulse injection of diesel.

The influence of reduction in the concentration of CO2 in biogas on performance, emissions and combustion in a constant speed spark ignition (SI) engine was studied experimentally. A lime water scrubber was used to lower carbon dioxide (CO2) levels from 41% in biogas to 30% and 20%. The tests covered the range of equivalence ratios from rich to the lean operating limit at a constant speed of 1500 rpm and at compression ratio of 13:1 with a masked valve to enhance swirl. With a reduction in the CO2 level there was a significant improvement in the performance and reduction in emissions of hydrocarbons (HC) particularly with lean mixtures. The lean limit of combustion also gets extended. Heat release rates indicated enhanced combustion rates, which are mainly responsible for the improvement in thermal efficiency. A reduction in the CO2 level by 10% seemed to be sufficient for reducing HC levels and the NO levels were also not significantly raised. The spark timings were to be retarded by about 5° when the CO2 concentration was decreased by 10%. © 2007.

A turbocharged three cylinder automotive common rail diesel engine was modified to operate in the n-butanol diesel dual fuel mode. The quantity of butanol injected by the port fuel injectors and the rail pressure, injection timing and number of injection pulses of diesel were varied using open engine controllers. Experiments were performed in the dual fuel mode at a constant speed of 1800 rpm at varying BMEPs. Butanol to diesel energy share (BDES) was varied and the injection timing of diesel was always set for highest brake thermal efficiency (BTE). Single pulse injection (SPI) and two pulse injection (TPI) of diesel were evaluated. In SPI with increase in butanol diesel energy share (BDES), BTE remained unchanged. At high loads and high BDES the heat release rate variation indicated that butanol auto ignited before diesel with both SPI and TPI of diesel. NO emission always decreased because of reduced temperatures due to evaporation of butanol. Butanol also reduced the smoke levels except at high loads. HC levels were always higher. With optimized injection parameters TPI of diesel resulted in lower NO, similar smoke and BTE with lesser rate of pressure rise as compared to SPI of diesel.

Hydrogen was added in small amounts (5%, 10% and 15% on the energy basis) to biogas and tested in a spark ignition engine at constant speed at different equivalence ratios to study the effects on performance, emissions and combustion. Hydrogen significantly enhances the combustion rate and extends the lean limit of combustion of biogas. There is an improvement in brake thermal efficiency and brake power. However, beyond 15% hydrogen the need to retard the ignition timing to control knock does not lead to improvements at high equivalence ratios. Significant reductions in hydrocarbon levels were seen. There was no increase in nitric oxide emissions due to the use of retarded ignition timing and the presence of carbon dioxide. Peak pressures and heat release rates are lower with hydrogen addition as the ignition timing is to be retarded to avoid knock. There is a reduction in cycle-by-cycle variations in combustion with lean mixtures. On the whole 10% hydrogen addition was found to be the most suitable. © 2006 International Association for Hydrogen Energy.

Alcohols are widely used along with gasoline owing to their superior antiknock properties. Engine knocking depends on both fuel properties and operating conditions. The Research and Motor Octane Numbers widely used to characterize antiknock potential are calculated under specific operating conditions. In this work, a method that incorporates the effects of actual operating conditions is developed, used to determine the antiknock potential when ethanol and gasoline are used in a port fuel injected engine using simultaneous and pre-blended injection modes. Experimental results are used to build and validate an analytical model of the engine which is used to study the antiknock benefits in terms of "Effective Octane Number" (ONEff). Experiments are conducted using a newly developed injection system which utilizes separate injectors for ethanol and gasoline. This method could capture the effects of engine operating conditions in calculating antiknock benefits. Higher ethanol fractions showed better antiknock capabilities. ONEff increases from 90 to 105 units when the ethanol quantity is increased from 0 to 100% by mass, but the effect diminishes after 50%. Hence, considering antiknock benefits, the use of 50% ethanol in gasoline is recommended. ONEff of the pre-blended injection case was only 0.8 units higher, indicating the similar antiknock potential of both injection strategies.

In this work biogas was used in a HCCI engine with charge temperature and amount of diesel injected into the intake manifold being used to control combustion. The presence of CO2 in biogas suppresses the high heat release rates encountered with neat diesel fuelling in HCCI engines. Normally biogas use leads to a drop in thermal efficiency in both SI and CI engines. However, present results indicate that thermal efficiencies close to diesel engine values can be obtained in the HCCI mode. The NO level was less than 20 ppm and the smoke level was less than 0.1 BSU at all conditions. The best energy ratio was 50%. HC levels were very high and were lowered when the charge temperature was raised. A charge temperature of about 80-135 °C was needed, which can be attained though heating by exhaust gases. On the whole the HCCI mode can be a viable option to utilize biogas in a diesel engine. © 2009 Elsevier Ltd. All rights reserved.

In this work, biogas was used in a compression ignition (CI) engine in the homogeneous charge compression ignition (HCCI) mode as well as in the dual-fuel mode together with diesel. In the HCCI mode, the charge temperature and amount of diesel injected into the intake manifold were used to control combustion. The presence of carbon dioxide in biogas suppresses the high heat release rates normally encountered in neat-diesel-fuelled HCCI engines. Efficiencies close to diesel operation together with extremely low levels of nitric oxide (NO) and smoke were attained in a brake mean effective pressure (BMEP) range from 2.5 bar to 4 bar in the biogas-diesel homogeneous charge compression ignition (BDHCCI) mode. Proper control over the charge temperature was essential. Thermal efficiency was higher and NO, hydrocarbon, carbon monoxide, and smoke levels were lower than in the biogas-diesel dual-fuel mode. Thus, the BDHCCI mode is a viable option for using biogas in CI engines in the medium-load ranges. Operation of the engine in the CI mode with diesel below a BMEP of 2.5 bar, then in the HCCI mode up to a BMEP of 4 bar, and in the dual-fuel mode at higher BMEPs could lead to good overall performance and low emissions. © IMechE 2009.

In this work, experiments were conducted on a homogeneous charge compression ignition (HCCI) engine with acetylene as the sole fuel at different power outputs. Initially, the intake air was heated to different temperatures in order to determine the optimum level at every output. Charge temperatures needed were in the range of 40-110 °C from no load to a BMEP (Brake Mean Effective Pressure) of 4 bar. Subsequently, exhaust gas re-circulation (EGR) was done at the identified charge temperatures and brake thermal efficiency was found to improve. At high BMEPs, use of EGR led to knocking. Thus, fine control over charge temperature and EGR quantity is needed at these conditions. Nitric oxide and smoke levels were very low. However, HC levels were high at about 1700-2700 ppm. Brake thermal efficiencies were comparable to or even better than the compression ignition mode of operation. © 2009 Elsevier Ltd. All rights reserved.

Internal combustion engines running on gaseous fuels produce low torque because the inducted gaseous fuel displaces air and reduces the volumetric efficiency. This can be overcome by injecting the gaseous fuel directly into the cylinder after the intake of air is completed. This work is a step in developing and demonstrating a cost effective system, as such systems are not readily available for small applications. A low-pressure gas injector was mounted on the cylinder barrel of a fully instrumented dual fuel engine. Its location is such that the injector will be exposed to the cylinder gases about 65.5 degrees before bottom dead center, where the cylinder pressure and temperature will be relatively low. An electronic controller was also developed to time the injection process to occur after the intake valve closes and also to control the duration of injection (quantity). Experiments were conducted with LPG (Liquefied petroleum gas) as the primary fuel that was injected with this new system and diesel as the pilot fuel at the rated speed of 1500 rpm with different amounts of LPG at 80% and 100% load. Comparisons of performance, combustion and emissions with the conventional manifold injection of LPG were done. The system allowed greater amounts of LPG to be used without knock as compared to manifold injection. On the whole the developed system has potential for application in small dual fuel and spark ignited gas engines and can be taken up for further optimization.