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.

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.

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 experimental work the effect of double injection of diesel in a biogas-diesel partially premixed charge compression ignition (BDPPCCI) engine was studied. Biogas was inducted along with air while diesel was injected through a common rail system using an open electronic control unit. Experiments were done at a fixed brake mean effective pressure of 2 bar and an intake charge temperature of 40°C. The effect of start of injection (SOI) of first and second injection pulses and also the biogas energy share (BGES) were evaluated. Experiments were also done in the BDPPCCI mode with diesel being injected in a single pulse and in the biogas-diesel dual fuel (BDDF) mode for comparison. The thermal efficiency in the BDPPCCI mode was better with double injection of diesel as compared to single pulse injection due to better combustion phasing. Improved charge homogeneity and reduced wall wetting of diesel lowered the smoke emission levels with split injection. Nitric oxide (NO) and hydrocarbon (HC) emissions were similar between split and single injection in the BDPPCCI mode. Further the BDPPCCI mode was significantly better than the BDDF in terms of NO and HC emissions. However, at high BGES the thermal efficiency with the BDPPCCI mode with single pulse injection was better than the BDDF mode. With split injection this threshold energy share could be lowered and thus the operating range of energy ratios was widened in the BDPPCCI mode.

The RCCI (Reactivity Controlled Charge Compression Ignition) mode of operation of an IC engine using biogas and diesel as fuels has the potential to offer high efficiencies and low NOx and soot emissions. One of the drawbacks while converting conventional diesel engines to run in this mode is the wall wetting of the diesel that has to be injected early in the compression stroke. This leads to high THC emissions and lubricating oil dilution. In this work a twin cylinder turbocharged, common rail diesel engine was modified to accommodate a newly developed Narrow angle Injector (NI) for early injection of diesel without wall wetting, along with the existing Wide angle Injector (WI). Biogas was also injected into the intake manifold and the engine was run in the RCCI mode. The effectiveness of this novel twin injector dual fuel RCCI concept has been experimentally assessed at different biogas energy shares under a BMEP of 3 bar and at a constant engine speed of 1500 rpm. The different biogas – diesel modes considered were the conventional dual fuel mode (CDF), RCCI with the WI alone, RCCI with the NI alone and finally RCCI with the combined NI-WI. In the biogas diesel RCCI mode the use of only the WI resulted in low efficiency, high THC and smoke emissions due to cylinder wall wetting of diesel. Though the use of only NI in this mode could eliminate cylinder wall wetting, the diesel directly hitting the piston bowl resulted in poor performance. However, the combination of NI and WI resulted in high BTE and extremely low levels of NOx emissions and lower THC as compared to the CDF mode. The range of injection timings for the NI was 90° to 45° bTDC while for the WI it was 42° to 4° bTDC when the energy share of biogas was changed. Thus the use of two injectors with wide and narrow injection spray angles for diesel gave enhanced flexibility in operating at widely different injection timings as required in biogas diesel RCCI operation.

A single cylinder diesel engine was modified to operate as a biogas operated spark ignition engine. The engine was operated at 1500 rpm at throttle opening of 25% and 100% at various equivalence ratios. The tests were covered a range of equivalence ratios from rich to the lean operating limit and a number of compression ratios. The spark timing was set to MBT (Minimum advance for Best Torque). The performance, emission and combustion characteristics with different compression ratios are compared. It has been found from the results that the higher the compression ratio, the higher the brake thermal efficiency. When the compression ratio was above a critical value of 13:1, brake power and thermal efficiency increased little. At higher compression ratios above 13:1, increased NOx, HC, and CO emissions were measured. Power and thermal efficiency reached their highest values with the compression ratio between 13:1 and 15:1 and the equivalence ratio between 1.08 and 0.95. Under these conditions, HC and CO emissions were low but the NOx values were high. Power and thermal efficiency reduced for leaner mixtures. The MBT spark timing is retarded with increase in compression ratio. The peak pressure decreases, as the mixture becomes lean at all the compression ratios. The peak pressure is higher with higher compression ratio. Increase in compression ratio leads to high heat release rate. © 2012 Elsevier Ltd. All rights reserved.

The influence of swirl on the performance, emissions and combustion in a constant speed Spark Ignition (SI) engine was studied experimentally. A single cylinder diesel engine was modified to operate as a biogas operated spark ignition engine. The engine was operated at 1500 rpm at throttle opening of 25% and 100% at various equivalence ratios. The tests covered a range of equivalence ratios from rich to lean operating limits and also at an optimum compression ratio of 13:1 with normal and masked intake valve to enhance swirl. The spark timing was set to MBT (Minimum advance for Best Torque). It was found that masked valve configuration enhanced the power output and brake thermal efficiency at full throttle. The lean limit of combustion also got extended. Heat release rates indicated enhanced combustion rates with masked valve, which are mainly responsible for the improvement in thermal efficiency. NO level increased with masked valve as compared to normal configuration. The spark timings were to be retarded by about 6 CA and 4 CA when compared to normal configuration at 25% and 100% throttle respectively.

A biogas fuelled constant speed spark ignition engine was studied experimentally for its performance, emissions and combustion, under the influence of an increased oxygen concentration in the intake air and results were compared. A single cylinder diesel engine was modified for the purpose and was operated at 1500 rpm, maintaining the throttle opening at 25% and 100% for various equivalence ratios. The oxygen level in the intake air was kept at 21%, 22% and 23% by volume and the tests also maintained a compression ratio of 13:1 with a masked valve. A significant improvement in the brake thermal efficiency and brake power was observed at higher oxygen levels. The peak brake thermal efficiencies with 22% and 23% oxygen levels are 27% and 28% respectively, whereas with 21% oxygen level at the same equivalence ratio the efficiency to be 26.2%. The lean limit also got extended and at higher oxygen levels increased NOx, reduced HC and CO emissions were measured. Heat release rates showed enhanced combustion rates, which in turn were indicators for improvised thermal efficiencies. To maintain the NOx emissions well inside the set standards, a mere increase of 1%–2% oxygen level was observed to be ideal.