The impacts of compression ratio on the performance and emissions of ice powered by oxygenated fuels: A review

Energy sources are becoming a governmental issue, with cost and stable supply as the main concern. Oxygenated fuels production is cheap, simple and eco-friendly, as a well as can be produced locally, cutting down on transportation fuel costs. Oxygenated fuels are used directly in an engine as a pure fuel, or they can be blended with fossil fuel. The most common fuels that are conceded under oxygenated fuels are ethanol, methanol, butanol Dimethyl Ether (DME), Ethyl tert-butyl ether (ETBE), Methyl tert-butyl ether (MTBE) and biodiesel that have attracted the attention of researchers. Due to the higher heat of vaporization, high octane rating, high flammability temperature, and single boiling point, the oxygenated fuels have a positive impact on the engine performance, combustion, and emissions by allowing the increase of the compression ratio. Oxygenated fuels also have a considerable oxygen content that causes clean combustion. The aim of this paper was to systematically review the impact of compression ratio (CR) on the performance, combustion and emissions of internal combustion engines (ICE) that are operated with oxygenated fuels that could potentially replace petroleum-based fuels or to improve the fuel properties. The higher octane rating of oxygenated fuels can endure higher compression ratios before an engine starts knocking, thus giving an engine the ability to deliver more power efficiently and economically. One of the more significant findings to emerge from this review study was the slight increases or decreases in power when oxygenated fuel was used at the original CR in ICE engines. Also, CO, HC, and NOx emissions decreased while the fuel consumption (FC) increased. However, at higher CR, the engine performance increased and fuel consumption decreased for both SI and CI engines. It was seen the NOx, CO and CO₂ emissions of oxygenated fuels decreased with the increasing CR in the SI engine, but the HC increased. Meanwhile, in CI engine, the HC, CO and NOx decreased as the CR increased with biodiesel fuel.     

A review of hydrogen as a compression ignition engine fuel

Diesel fuelled engines emit higher levels of carbon dioxide and other harmful air pollutants (such as noxious gases and particulates) per litre of fuel than gasoline engines. This fact, combined with the recent diesel emission scandal and the rumours of more widespread cheating by automotive manufacturers have initiated a long discussion about the future and sustainability of diesel engines.Improving the compression ignition engine is a direct way of going green. Reducing the harmful emissions can be achieved by future developments in the engine technology but also the implementation of alternative fuels. Hydrogen is a renewable, high-efficient and clean fuel that can potentially save the future of diesel-type engines. The evolution of high-efficiency renewable hydrogen production methods is the most important path for the start of a new hydrogen era for the compression ignition engine that can improve its sustainability and maximum efficiency.This paper provides a detailed overview of hydrogen as a fuel for compression ignition engines. A comprehensive review of the past and recent research activities on the topic is documented. The review focuses on the in-cylinder combustion of hydrogen either as a primary fuel or in dual fuel operation. The effects of injection strategies, compression ratio and exhaust gas recirculation on the combustion and emission characteristics of the hydrogen fuelled engine are fully analysed. The main limitations, challenges and perspectives are presented.     

Analysis of biogas compression system dynamics

The use of biogas for energy production has progressively increased in recent years, due to an increasing interest both in agricultural and energy policies of many industrialized countries. Biogas compression by means of natural gas infrastructure seems the most immediate solution, but could also lead to problems due to the different physical properties of the two gases. In this paper, a non-linear one-dimensional modular dynamic model is developed and used for the simulation of compression system transient behavior. The arrangement consists of a main line, where the compressor operates, and an anti-surge control, which consists of a recycle loop activated by a fast acting valve. Different maneuvers (start-up, normal operation, emergency shutdown and operating point variation) are simulated by using two different working fluids (methane and biogas). Simulations prove that the design of the surge protection system should consider the fluid to be elaborated. Moreover, system predisposition to surge increases as the ratio between system volumes and the inertia of the rotating masses increases.     

An experimental study of a direct injection compression ignition hydrogen engine

This paper describes the development of an experimental setup for the testing of a diesel engine in the direct injection hydrogen-fuelled mode. Test results showed that the use of hydrogen direct injection in a diesel engine gave a higher power to weight ratio when compared to conventional diesel-fuelled operation, with the peak power being approximately 14% higher. The use of inlet air heating was required for the hydrogen-fuelled engine to ensure satisfactory combustion, and a large increase in the peak in-cylinder gas pressure was observed. A significant efficiency advantage was found when using hydrogen as opposed to diesel fuel, with the hydrogen-fuelled engine achieving a fuel efficiency of approximately 43% compared to 28% in the conventional, diesel-fuelled mode. A reduction in nitrogen oxides emission formation of approximately 20% was further observed.     

Combustion and emission characteristics of a hydrogen-diesel dual-fuel engine

Hydrogen generated from renewable sources is an eco-friendly fuel that can be used in automotive industry or for energy generation purposes. Hydrogen is a high-energy content gas and its carbonless chemical structure can provide significant benefits of high thermal efficiency and near zero or very low carbon emissions when combusted with other fuels.In this study, the implementation of hydrogen fuel was tested at low and medium operating loads in a heavy-duty hydrogen-diesel dual-fuel engine. The paper provides a detailed experimental analysis of the effects of hydrogen energy share ratio and various combustion strategies such as exhaust gas recirculation, diesel injection pressure and diesel injection patterns.At low load conditions, engine operation with an H₂ energy share ratio of up to 98% was achieved without any engine operation implications. This condition provided a simultaneous reduction of carbon and NOx emission of over 90% while soot emissions were dropped by 85% compared to the conventional diesel-only operation. At medium load, the increased NOx emission due to the high energy content of hydrogen fuel was found to be the primary challenge.     

Low-load hydrogen-diesel dual-fuel engine operation – A combustion efficiency improvement approach

Hydrogen-diesel dual-fuel operation can provide significant benefits to the performance and carbon-based emissions formation of compression-ignition engines. The wide flammability range of hydrogen allows engine operation at extremely low equivalence ratios while its high diffusivity and flame speed promote wide range combustion inside the cylinder. Nonetheless, despite the excellent properties of hydrogen for internal combustion, unburned hydrogen emissions and poor combustion efficiency have been previously observed at low-load conditions of compression ignition engines.The focus of the present study is to assess the effects of different engine operation and diesel injection parameters on the combustion efficiency of a heavy-duty dual-fuel engine while observing their interactions with the brake thermal efficiency (BTE) and emissions formation of the engine. In an attempt to reduce the unburned hydrogen rates at the exhaust of the engine, exhaust gas recirculation (EGR) and different diesel injection strategies were implemented. Statistical methods were applied in this study to reduce the experimental time.The results show a strong connection between unburned hydrogen rates, combustion and brake thermal efficiencies with the EGR rate. Higher EGR rates increase the intake charge temperature and provide improved hydrogen combustion and fuel economy. Operation of the dual-fuel engine at low-load with high EGR rate and slightly advanced main diesel injection can deliver simultaneous benefits to most of the harmful emissions and the BTE of the engine. Despite the efforts to achieve optimal engine operation at low loads, the combustion efficiency for most of the tested cases was in the range of 90%. Thus, increased hydrogen rates should be avoided as the benefits of the dual-fuel operation are weak at low-load conditions.     

Experimental investigation of the effects of simultaneous hydrogen and nitrogen addition on the emissions and combustion of a diesel engine

Overcoming diesel engine emissions trade-off effects, especially NO_x and Bosch smoke number (BSN), requires investigation of novel systems which can potentially serve the automobile industry towards further emissions reduction. Enrichment of the intake charge with H₂ + N₂ containing gas mixture, obtained from diesel fuel reforming system, can lead to new generation low polluting diesel engines.     

Assessment of the co-combustion process of ammonia with hydrogen in a research VCR piston engine

The presented work concerns experimental research of a spark-ignition engine with variable compression ratio (VCR), adapted to dual-fuel operation, in which co-combustion of ammonia with hydrogen was conducted, and the energy share of hydrogen varied from 0% to 70%. The research was aimed at assessing the impact of the energy share of hydrogen co-combusted with ammonia on the performance, stability and emissions of an engine operating at a compression ratio of 8 (CR 8) and 10 (CR 10). The operation of the engine powered by ammonia alone, for both CR 8 and CR 10, is associated with either a complete lack of ignition in a significant number of cycles or with significantly delayed ignition and the related low value of the maximum pressure p_max. Increasing the energy share of hydrogen in the fuel to 12% allows to completely eliminate the instability of the ignition process in the combustible mixture, which is confirmed by a decrease in the IMEP uniqueness and a much lower p_max dispersion. For 12% of the energy share of hydrogen co-combusted with ammonia, the most favorable course of the combustion process was obtained, the highest engine efficiency and the highest IMEP value were recorded. The conducted research shows that increasing the H₂ share causes an increase in NO emissions, for both analyzed compression ratios.     

Experimental investigation of the effects of separate hydrogen and nitrogen addition on the emissions and combustion of a diesel engine

An experimental investigation of the effects of separate hydrogen and nitrogen addition on the emissions and combustion of a diesel engine was performed and the results are presented in the current paper.     

Effect of ignition timing and compression ratio on the performance of a hydrogen–ethanol fuelled engine

This paper presents the results obtained of a compression ignition engine (modified to run on spark ignition mode) fuelled with hydrogen–ethanol dual fuel combination with different percentage substitutions of hydrogen (0–80% by volume with an increment of 20%) under variable compression ratio conditions (i.e. 7:1, 9:1 and 11:1) by varying the spark ignition timing at a constant speed of 1500 rpm. The various engine performance parameters studied were brake specific fuel consumption, brake mean effective pressure and brake thermal efficiency. It was found from the present study that for specific ignition timing the brake mean effective pressure and the brake thermal efficiency increases with the increase of hydrogen fraction in ethanol and all hydrogen substitutions showed the maximum increase in brake thermal efficiency and reduction in brake specific fuel consumption value at around 25^° CA advanced ignition timing. The best operating conditions were obtained at a compression ratio of 11:1 and the optimum fuel combination was found to be 60–80% hydrogen substitution to ethanol.     

Effect of ethanol–gasoline blends on engine performance and exhaust emissions in different compression ratios

Renewable energy sources for the gasoline engines alcohols gain importance recently. These renewable energy sources have attracted the attention of researchers as alternative fuel due to their high octane number. In addition, these are also clean energy sources and can be obtained from the biomass alcohols with low carbon like ethanol. In this study, the effect of compression ratio on engine performance and exhaust emissions was examined at stoichiometric air/fuel ratio, full load and minimum advanced timing for the best torque MBT in a single cylinder, four stroke, with variable compression ratio and spark ignition engine.     

Novel heavy duty engine concept for operation dual fuel H2–NH3

A prior paper has presented a novel design of a heavy duty truck engine fuelled with H₂. In this design, the customary in-cylinder Diesel injector and glow plug are replaced with a main chamber fuel injector and a jet ignition pre-chamber. The jet ignition pre-chamber is a small volume that is connected to the in-cylinder through calibrated orifices accommodating another fuel injector and a glow or a spark plug that controls the start of combustion. This design permits to operate the engine in four different modes: traditional compression ignition (CI), diffusion, Diesel-like (M₁); mixed gasoline/Diesel-like (M₂); traditional spark ignition (SI), premixed, gasoline-like (M₃); premixed, homogeneous charge compression ignition HCCI-like (M₄). In the mode diffusion with jet ignition (M₁), an injection occurs in the jet ignition pre-chamber before the main chamber fuel is injected and the engine operates therefore mostly Diesel-like. In the mode mixed diffusion/premixed Diesel/gasoline-like (M₂) an injection occurs in the jet ignition pre-chamber after only part of the main chamber fuel is injected and mixed with air. In the mode premixed with jet ignition (M₃), an injection occurs in the jet ignition pre-chamber after the main chamber fuel is injected and mixed with air and the engine operates gasoline-like. Finally, in the mode premixed without jet ignition (M₄), no injection occurs in the jet ignition pre-chamber and the engine operates HCCI-like. Modelling results have already been presented and discussed with H₂ as the main chamber and pre-chamber fuel. This paper considers the option to accommodate a second main chamber injector that will inject the NH₃ that will then burn in air thanks to the hot combusting gases from the combustion of H₂ and air using the modes M₁ and M₂ described above. The mode M₃ also of interest is not considered here. First results of simulations show the opportunity to achieve better than Diesel fuel energy conversion efficiency thanks to the reduced heat losses of the “cold burning” NH₃ and suggest to perform the experiments needed to further support the findings.     

Biogas scrubbing, compression and storage: perspective and prospectus in Indian context

Biogas is a clean environment friendly fuel. Raw biogas contains about 55–65% methane (CH₄), 30–45% carbon dioxide (CO₂), traces of hydrogen sulfide (H₂S) and fractions of water vapours. Presently, it can be used only at the place where it is produced. There is a great need to make biogas transportable. This can be done by compressing the gas in cylinders which is possible only after removing its CO₂, H₂S and water vapour components. Pilot level trials to compress the biogas have been carried out by a number of earlier investigators working on the subject. This paper reviews the efforts made to improve the quality of biogas by scrubbing CO₂ and the results obtained. There is a lot of potential if biogas could be made viable as a transport vehicle fuel like CNG by compressing it and filling into cylinders after scrubbing and drying. Thus the need emerges for a unified approach for scrubbing, compressing and subsequent storage of biogas for wider applications.