Biogas Fuelled Spark Ignition Engine Research Articles

Enhancement of Low Operating Load Limit and Engine Characteristics by Hydrogen Addition in a Biogas-Fueled Spark-Ignition Engine

Abstract Biogas is a renewable gaseous fuel and has the potential to replace fossil fuels for spark-ignition engines; however, a higher volumetric proportion of CO2 in biogas degrades the engine characteristics significantly. Biogas upgradation techniques are limited by higher fuel costs, and strenuous modifications would be required for improving engine physical parameters. In this study, experimental investigations were performed with hydrogen-enriched biogas to enhance low operating load limit and engine characteristics, and to the best of authors' knowledge, studies related to operating range and low load enhancement by hydrogen addition in biogas fueled engines are not reported in literature. Gaseous-fuels blending setup was developed to fabricate the gaseous fuel mixtures in desired proportions and moderate amounts of hydrogen (5, 10, 20, and 30% by vol.) were blended with biogas. The experiments were conducted on a single-cylinder SI engine operated at the compression ratio of 10:1 and 1500 rpm for stationary applications. It was found that the coefficient of variation (COV) of indicated mean effective pressure decreased from 10% in case of biogas to 8.69, 6, 3.05, and 1.66%, respectively, for 5, 10, 20, and 30% hydrogen cases at 6 N·m loading condition. Low operating load limit enhanced from 6 N·m in case of biogas to 5.3, 2.2, 1.5, and 0.8 N·m, respectively, for 5, 10, 20, and 30% of hydrogen share in the fuel mixture and brake thermal efficiency also improved with hydrogen enrichment. Carbon-based emissions decreased with hydrogen addition, whereas oxides of nitrogen increased but it was well below the baseline case with pure methane. Overall results indicated that hydrogen enrichment enhances the low load limit and engine characteristics of biogas-fueled SI engines for stationary power generation applications in rural areas.

Experimental and computational study on the enhancement of engine characteristics by hydrogen enrichment in a biogas fuelled spark ignition engine

Limitations on the upgradation of biogas to biomethane in terms of cost effectiveness and technology maturity levels for stationary power generation purpose in rural applications have redirected the research focus towards possibilities for enhancement of biogas fuel quality by blending with superior quality fuels. In this work, the effect of hydrogen enrichment on performance, combustion and emission characteristics of a single-cylinder, four-stroke, water-cooled, biogas fuelled spark-ignition engine operated at the compression ratio of 10:1 and 1500 rpm has been evaluated using experimental and computational (CFD) studies. The percentage share of hydrogen in the inducted biogas fuel mixture was increased from 0 to 30%, and engine characteristics with pure methane fuel was considered as a baseline for comparative analysis. The CFD model is developed in Converge CFD software for a better understanding on combustion phenomenon and is validated with experimental data. In addition, the percentage share of hydrogen enrichment which would serve as a compromise between biogas upgradation cost and engine characteristics is also identified. The results of study indicated an enhancement in combustion characteristics (peak in-cylinder pressure increased; COVIMEP reduced from 9.87% to 1.66%; flame initiation and combustion durations reduced) and emission characteristics (hydrocarbon emissions reduced, and NOx emissions increased but still lower than pure methane) with increase in hydrogen share from 0 to 30% in biogas fuelled SI engine. Flame propagation speed increased and combustion duration reduced with hydrogen supplementation and the same was evident from the results of the CFD model. Performance of the engine increased with increase in hydrogen share up to 20% and further increment in hydrogen share degraded the performance, owing to heat losses and the enhancement in combustion characteristics were relatively small. Overall, it was found that 20% blending of hydrogen in the inducted biogas fuel mixture will be effective in enhancing the engine characteristics of biogas fuelled engines for stationary power generation applications and it holds a good compromise between biogas upgradation cost and engine performance.

Ignition timing and compression ratio as effective means for the improvement in the operating characteristics of a biogas fueled spark ignition engine

In the current investigation, a four stroke, variable speed, single cylinder, variable compression ratio (VCR) SI engine is operated with raw biogas at wide open throttle (WOT) condition and at five different CRs ranging from CR 10 to CR 14 over the operating speed range of the engine. The ignition timing (IT) of the engine is also varied from 23○CA to 47○CA before top dead centre (bTDC) at each operating CR. The optimized operating CR and IT of the engine are obtained through series of experiments and its effects on the performance, combustion and emission characteristic are analysed herein. The rise in operating CR from CR 10 to CR 12 enhanced the power output and efficiency of the biogas fueled SI engine by 12.72% and 5.68%, respectively and reduced fuel consumption by 5.42% at 1400 rpm. Enhancing the CR from CR 10 to CR 12, limited the intensification of NOx and unburnt hydrocarbon emission by 10.17% and 15.6%, respectively at 1400 rpm. Hence, CR 12 is recommended as the optimum CR and its combination with 1400 rpm and WOT setting is recommended as the best operating condition of the engine.

Combined impact of compression ratio and re-circulated exhaust gas on the performance of a biogas fueled spark ignition engine

The usage of biogas as a potential fuel in a spark ignition (SI) engine is the theme for the present study. The exhaust gas recirculation (EGR) is a significant technique for improving the performance of the SI engine. Thus, the novelty of the experimental investigations lies in implementing the EGR technique for emission control of the biogas-fueled engine. The raw biogas (52% methane and 47% carbon dioxide), obtained from a biogas digester (using cow dung as the source), was the engine fuel for a four stroke, water cooled, variable compression ratio SI engine set-up. Here, the engine performance and emission related parameters were measured. When operated in the raw biogas mode at an optimum spark timing of 45 °CA before the top dead center, the engine produced maximum torques of 11 N m, 14 N m, and 16 N m for compression ratios 8, 9, and 10, respectively. The effect of different EGR rates on the emission control was also investigated. The net heat release rate without EGR was found to be 22.623J/°CA at 368 °CA, which further reduced to 14.233 J/°CA at 386 °CA for EGR10. Moreover, it was clearly evident that low EGR rates (below 10%) were effective in reducing NOX significantly, with minor compromise in power and brake specific fuel consumption. But the emissions of hydrocarbon and carbon monoxide were found to be higher with the increase in EGR. The operation of the engine with medium or heavy EGR rates resulted in issues related to intense pressure fluctuations and large cycle-to-cycle variation in performance. Thus, the present investigations recommend the use of low EGR (below 10%) in a biogas-based engine for lower NOX emission and better fuel efficiency.

Ignition advancement study for optimized characteristics of a raw biogas operated spark ignition engine

ABSTRACT In the current investigation, raw biogas obtained from rural sectors was used as the alternative to gasoline fuel in the spark ignition (SI) engine. The performance and efficiency are mainly dependent on the combustion phasing for which “ignition timing” is an effective tool in a SI engine. Hence, the objective of the present work is to understand the effect of “variable ignition timing” for a biogas-fueled SI engine. For this purpose, a single cylinder, 4-stroke, SI engine of rated power 4.5 kW was operated with raw biogas at a compression ratio (CR) of 10. By maintaining a speed of 1650 rpm, the engine was operated in wide open (WOT) and part throttle (PT) mode with an equivalence ratio of 0.81 and 0.83, respectively. It was observed that the biogas fueled SI engine was found to be operative only within the ignition advance (IA) range of 33–47° CA bTDC both in WOT and PT conditions. The results showed optimal brake power (BP), brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) are achieved at 45° CA bTDC. The average peak cylinder pressure, neat heat release rate (NHRR) and mean gas temperature (MGT) are also observed to be maximum while CO and HC emission at this point of IA were found to be minimum. Due to controlled and complete combustion, CO2 and NOx concentration in the exhaust emission were found to be higher at this point of ignition timing.

Interactive control of combustion stability and operating limits in a biogas-fueled spark ignition engine with high compression ratio

The use of high compression ratios on spark ignition engines enables the increase of thermal efficiency, but also contributes to the reduction of high load limit because of the higher auto-ignition tendency in the end-gas. Gaseous fuels provide a good option to expand the high load limits because of their high octane ratings, mostly in small engines. Biogas is a renewable fuel, mainly composed by $$\hbox {CH}_{4}$$ and $$\hbox {CO}_{2}$$ that exhibits high auto-ignition temperature and slow laminar flame speed. When biogas is burned in spark ignition engines partial and total misfire at low loads counteract the benefits achieved at high loads in which knocking combustion is reduced, hence the design of an effective control of the operating range based on the real-time observation of combustion instabilities is desirable. This paper presents an interactive control of the safe operating range through the modification of the spark time, equivalent ratio and throttle valve opening, taking as feedback the combustion instabilities, which are calculated from the in-cylinder pressure evolution for a biogas-fueled high compression ratio spark ignition engine. The interactive control was tested on a modified diesel engine converted to spark-ignition, original compression ratio of 15.5:1 and fueled with biogas. Control was able to keep a safe operating range with a maximum throttle valve opening of 39%, equivalence ratios within 0.6 and 1, and spark advances in the range of 329–358 crank angle degree. The coefficient of variation of IMEP was lower than 8%, whereas the maximum average knocking intensity was close to 2.5.

Experimental studies on the effects of enhancing the concentration of oxygen in the inducted charge of a biogas fuelled spark ignition engine

Abstract 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.

Effect of swirl on the performance and combustion of a biogas fuelled spark ignition engine

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 1500rpm 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.

Effect of compression ratio on the performance and combustion of a biogas fuelled spark ignition engine

A single cylinder diesel engine was modified to operate as a biogas operated spark ignition engine. The engine was operated at 1500rpm 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.

Effect of hydrogen addition on the performance of a biogas fuelled spark ignition engine

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.