Reactivity Controlled Compression Ignition Mode Research Articles

Dual fuel intelligent charge compression ignition (ICCI) combustion: Efficient and clean combustion technology for compression ignition engines

A brand-new combustion mode intelligent charge compression ignition (ICCI) was proposed to be expected for ultra-high efficiency and low emissions simultaneously. The introduce for conceptual model of ICCI mode aimed to realize flexible and controllable in-cylinder charge stratification fed by two complementary fuel, gasoline and diesel. To fulfill this unique dual-fuel combustion mode, two common-rail direct-injection systems were independently utilized on a modified single-cylinder engine, controlled by their own on-limits electronic control unit, respectively. Fundamentally experimental investigations on ICCI mode was conducted by the fuel ratio variation at 8 bar indicated mean effective pressure (IMEP). The experimental results showed that high indicated thermal efficiency close to 50% and low NOx emissions well below 0.12 g/kWh were simultaneously achieved at 85% gasoline ratio. Based on the optimal gasoline ratio, multi-injection strategies of ICCI mode can further improve thermal efficiency and emissions. Meanwhile, comparisons of ICCI with other combustion modes, including reactivity-controlled compression ignition (RCCI), G85 dual direct injection (DDI), G85, and G70 single direct injection (DI) strategies were carried out. In the similar operating conditions, ICCI combustion got better performance compared with other combustion modes, achieving about 2% increased indicated thermal efficiency in comparison to RCCI or DDI mode and near none NOx emissions compared with DI combustion. Prospectively, if it can be continually researched, ICCI has a large potential based on the further optimization in the future.

Influence of waste vegetable oil biodiesel and hexanol on a reactivity controlled compression ignition engine combustion and emissions

Abstract In the present work, biofuels produced from agricultural waste have been proposed as a substitute for petroleum-based fuel. Biodiesel produced from waste vegetable oil has been used alongside hexanol in a reactivity controlled compression ignition engine. The waste vegetable oil biodiesel was prepared by trans-esterification and was directly injected inside the cylinder. Hexanol was injected into the port during early suction stroke. A modified 1-cylinder water-cooled diesel engine was used for the tests. The modified engine was tested at medium load and rated load for injection pressures of 400, 500 and 600 bar. The proportion of hexanol to waste vegetable oil biodiesel was also varied to find the optimal combination. The results were mapped and analyzed with diesel operation at similar conditions. A maximum increase of 1.5% in thermal efficiency was observed compared to Diesel. Oxides of nitrogen and smoke emissions reduced simultaneously for biodiesel-hexanol combinations compared to diesel. Injection pressure of 500 bar and hexanol proportion of 30% at medium load and 60% at rated load were found to be optimum concerning lowest emissions. This study proposes that waste vegetable oil biodiesel and hexanol combination in reactivity controlled compression ignition mode can be an effective replacement for conventional fossil fuel.

Experimental Assessment of Effects of n-Butanol on Performance, Emission, and Combustion Characteristics of Mahua Oil Fueled Reactivity Controlled Compression Ignition (RCCI) Engine

The emission and combustion characteristics of diesel engine operated under reactivity controlled compression ignition (RCCI) mode are investigated in this study. A separate electronic fuel injector was mounted on the intake manifold of the engine meant for RCCI operation. RCCI mode of operation was conducted by injecting “n-butanol” as low reactivity fuel into the intake, and “mahua oil” as high reactivity fuel directly into the combustion chamber. Experimental results reported that smoke and nitric oxide (NO) emissions are significantly reduced by 45.4% and 33.1% through RCCI mode when compared with single fuel mode (mahua oil) at peak load. Carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions were substantially increased at part load conditions in RCCI mode by increasing n-butanol energy share, while both HC and CO emissions were reduced at maximum power output. About 6.2% increase in brake thermal efficiency (BTE) of the engine was found when operated in RCCI mode, with up to 20% of n-butanol share; beyond this energy share, a marginal drop in BTE was noted at peak load. A substantial rise in cylinder pressure and heat release rate (HRR) was found while operating in RCCI mode. At part load, ignition delay was found to be longer in RCCI operation, but at supreme load condition, it was reduced. It was concluded that RCCI mode of operation improved the engine’s performance and similarly reduced smoke and NO emissions.

Experimental, numerical and exergy analyses of a dual fuel combustion engine fuelled with syngas and biodiesel/diesel blends

This work investigates the effects of addition of syngas and biodiesel on a reactivity controlled compression ignition (RCCI) engine fuelled with diesel. Scanning electron microscopy (SEM) of exhaust particulate matter has been done to obtain particulate matter (PM) morphology. Energy and exergy analyses have been performed to observe energy and availability shares, and to provide directions for the energy recovery systems. Closed cycle combustion simulations have been performed to complement the experimental results and for an improved understanding of in-cylinder dynamics. Chemical and physical properties of three biodiesel samples have been analysed using elemental analysis, Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. Based on the initial study, used cooking oil based biodiesel blend (B20, 20% biodiesel) has been chosen in experiments. The optimal operating conditions for syngas/diesel and syngas/B20 in RCCI mode for different operating parameters have been investigated. Injection pressure, injection timing and pre-injection mass ratio have been modified to get improved combustion efficiency at mid-load. Syngas/diesel mode with an injection timing of 19° before top dead centre (bTDC) shows slightly higher brake thermal efficiency (BTE) with 22% and 77% lower oxides of nitrogen (NOx) and PM respectively as compared to conventional diesel combustion. In syngas/B20 mode, a maximum BTE of 24% has been observed for the case with a pre-injection at 50° bTDC with 30% mass fraction and 18° bTDC main injection timing. Syngas/diesel shows a reduction in primary soot particle count by about 67% and contains larger aggregates as compared to neat diesel.

An Experimental Investigation on the Influence of Port Injection at Valve on Combustion and Emission Characteristics of B5/Biogas RCCI Engine

High unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions, on account of the premixed air-fuel mixture entering the crevices and pre-mature combustion, are setbacks to reactivity-controlled compression ignition (RCCI) combustion at a low load. The influence of direct-injected B5 and port injection of biogas at the intake valve was, experimentally, examined in the RCCI mode. The port injection at the valve was to elevate the temperature at low load and eliminate premixing for reduced pre-mature combustion and fuel entering the crevices. An advanced injection timing of 21° crank angle before top dead centre and fraction of 50% each of the fuels, were maintained at speeds of 1600, 1800 and 2000 rpm and varied the load from 4.5 to 6.5 bar indicated mean effective pressure (IMEP). The result shows slow combustion as the load increases with the highest indicated thermal efficiency of 36.33% at 5.5 bar IMEP. The carbon dioxide and nitrogen oxides emissions increased, but UHC emission decreased, significantly, as the load increases. However, CO emission rose from 4.5 to 5.5 bar IMEP, then reduced as the load increases. The use of these fuels and biogas injection at the valve were capable of averagely reducing the persistent challenge of the CO and UHC emissions, by 20.33% and 10% respectively, compared to the conventional premixed mode.

An experimental evaluation of engine performance and emissions characteristics of a modified direct injection diesel engine operated in RCCI mode

This study explored methods to evaluate the test engine characteristics operated based on the reactivity controlled compression ignition (RCCI) technology to reduce fuel consumption and exhaust emissions, especially PM and NOx. Consequently, gasoline and diesel, respectively, considered as the low reactivity fuel (LRF) and high reactivity fuel (HRF), are injected in the intake manifold and combustion chamber. The experimental procedure is conducted at a constant speed of 2000 rpm, and brake mean effective pressure (BMEP) from low load 0.84 bar to high load 4.24 bar. The injection strategy is varied according to the engine loads. Indeed, at the low and medium engine load condition, the diesel fuel is injected double injection pulse, at the high load, the diesel fuel is injected single injection pulse. The injection timing is advanced from the top dead center (TDC) until knocking happens or the coefficient of variation (COV) higher than 10%, and maximum advanced injection timing is 65 crank angle degree (℃A) before the top dead center (BTDC). The results of advanced injection timing show that limit of advanced timing in low load is COV while at high load is knocking; at medium load, the diesel injection timing can be advanced to 65℃A BTDC. The exhaust emissions of CO and HC are higher than conventional diesel engines, while soot is hugely lower in all operating points. NOx emission is much dependent on injection timing, at 10 to 20℃A BTDC NOx highest, and approximately to the conventional diesel engine, NOx reduction when injection timing advanced.

Potential of bio-ethanol in different advanced combustion modes for hybrid passenger vehicles

The strong new restrictions in the vehicle CO2 emissions together with the instability of the fossil fuels reserves reinforces the necessity to continue developing high efficiency combustion engines that operate with renewable energy sources. Bio-ethanol appears as a potential fuel to replace well-established fossil fuels, such as gasoline, due to the overall carbon neutral emission. In addition, the high-octane number allows to increase the compression ratio of the engine to improve the thermal efficiency. Apart from the CO2, the emissions legislation restricts the NOx and particle matter emissions to ultra-low values, and they will continue decreasing down to almost zero. In this work, two advanced dual-fuel combustion modes using bio-ethanol as main fuel are studied. A pre-chamber ignition system (PCIS) using bio-ethanol and hydrogen, and a reactivity-controlled compression ignition (RCCI) combustion mode operating with bio-ethanol/diesel was selected due to the potential to reduce NOx emissions. These combustion technologies were studied by a numerical 0-D vehicle simulations in homologation and real-life driving cycles for a range extender hybrid powertrain. As a baseline, the original manufacturer spark ignition (SI) no-hybrid powertrain fueled with pure bio-ethanol was used. The powertrain components and control system were optimized to obtain the maximum overall vehicle efficiency, and low CO2-NOx emissions. Finally, a life cycle analysis (LCA) was performed to study the global potential of the bio-ethanol to reduce greenhouse gas (GHG) emissions. A battery electric vehicle (BEV) and a gasoline SI no-hybrid vehicle were added for comparison. The results show that the RCCI mode presents the highest potential to reduce the NOx emissions. However, the PCIS allows to reduce the tank to wheel CO2 emissions up to 60 g/km when high rates of H2 are used. The LCA-GHG for the vehicles using bio-ethanol is 50% and 95% lower than a BEV and SI-gasoline vehicle, respectively.

Reduced smoke and nitrogen oxide emissions during low-temperature combustion of ethanol and waste cooking oil

Air pollution is a major issue affecting the health of millions of citizens, notably in cities where pollutants are concentrated. Low-temperature combustion is a promising route to reduce nitrogen oxides and smoke emissions from compression ignition engines. Reduction in emissions during low-temperature combustion is known, yet emissions using oxygenated biofuels are poorly known. Therefore, I tested the potential reduction in emissions using oxygenated biofuels during low-temperature combustion, in the reactivity-controlled compression ignition mode. Ethanol, a low-reactivity fuel, was inducted in the intake manifold at 10% and 20% levels on energy basis, whereas waste cooking oil biodiesel, a high-reactivity fuel, was injected directly inside the cylinder. Results show a reduction in emission of nitrogen oxides up to 60%, and of smoke up to 29%. Nonetheless, unburned hydrocarbons and carbon monoxide emissions increased up to 2% at full load for biodiesel with 20% ethanol induction, compared to neat diesel and biodiesel.

A comprehensive study of fuel reactivity on reactivity controlled compression ignition engine: Based on gasoline and diesel surrogates

Based on three-component gasoline surrogates and five-component diesel surrogates, the effects of fuel reactivity of port injection fuel and direct injection fuel on combustion and emission characteristics of reactivity controlled compression ignition (RCCI) mode were systematically studied. The research octane number of port injection fuels and cetane number of direct injection fuels were modulated by changing the proportions of n-alkanes and iso-alkanes in surrogates. The results show that both the cetane number of direct injection fuel and research octane number of port injection fuel played the key role in the combustion phase of RCCI mode. When port injection fuel with research octane number ≤ 90, the low temperature heat release would occur. For premixed ratio of 0.8 and with RON70/CN55 as fuel, the CO emissions were the lowest (as low as 1585 ppm). Increasing the premixed ratio was an effective solution for suppressing NOx and particulate matter emissions. For premixed ratio increased from 0.4 to 0.8, the peak value of nuclear mode particulates decreased from 109 to 107. Increasing the cetane number of direct injection fuels or lowering the research octane number of port injection fuels inhibited the emissions of formaldehyde, acetaldehyde, ethylene, propylene, acetylene and 1,3-butadiene effectively. Port injection of low research octane number was beneficial to reducing indicated specific fuel consumption. Fuel combination with port injection of RON70, direct injection of CN55 and premixed ratio of 0.8 was recommended taking into account of fuel consumption, and regulated/unregulated gas emissions.

Reactivity Controlled Compression Ignition for clean and efficient ship propulsion

Reactivity Controlled Compression Ignition (RCCI) is commonly mentioned as a potential efficient and clean combustion concept. This study makes the first evaluation of natural gas-diesel RCCI combustion for mid-speed marine engines.A state-of-the-art dual-fuel engine with 350 mm bore diameter is the basis for numerical simulations. GT-Power is used to create a one-dimensional air-path model. RCCI is simulated using TNO's multi-zone combustion model incorporating detailed chemical kinetics. The simulations aim to optimize engine efficiency, with peak in-cylinder pressure and emissions as constraints.The study shows best-point Indicated Efficiency of 47.8% is achievable (@75% load) using RCCI mode on stock engine hardware, while meeting IMO Tier III's NOx limit. This performance is similar to the best contemporary marine gas engines, but RCCI also provides additional methane and CO emission reductions. Thus, RCCI combustion can meet Europe's new rigorous Stage V limits, offering significant improvements in a marine engine's GHG footprint.Crucially, the study indicates an engine using hardware optimized for RCCI could deliver outstanding indicated efficiencies of 52%, with emissions of below 1 g/kWh for all legislative species. This combination of high efficiency and ultra-low emissions would make RCCI combustion an attractive proposition for future marine propulsion and gen-set applications.

Comparative study of hydrogen addition effects on the natural-gas/diesel and natural-gas/dimethyl-ether reactivity controlled compression ignition mode of operation

Reactivity controlled compression ignition engines have been proven to have better performance comparing with other methods of low temperature combustion strategies. Using various fuels can have different outputs according to the chemical products and reactions as well as heating values. In this study, a numerical model beside experimental data as validation is used to investigate the effects of using additive on combustion characteristics of natural gas/dimethyl-ether and natural-gas/diesel Reactivity controlled compression ignition engines. Hydrogen is used as additive with 3, 6 and 9 percentage of heating value in the fuel mixture. Results show higher indicated mean effective pressure in all cases of using diesel as high reactivity fuel. In addition, investigation on the combustion characteristics shows that natural gas/diesel cases have advanced start of combustion and combustion phasing, while burn duration in natural gas/dimethyl-ether cases is higher than natural gas/diesel cases. By adding hydrogen species, it is seen that hydrogen has more effect on the start of combustion of natural gas/dimethyl-ether case where adding 9% hydrogen, advanced the start of combustion about 2 crank angle degree while this amount for natural gas/diesel case is about 0.3. In all cases of using diesel as high reactivity fuel, temperature is higher than dimethyl-ether used cases, which causes to produce more nitrogen oxides; for example, in 9% hydrogen addition, natural gas/diesel mode produced 0.54 g/kW/h nitrogen oxide more than natural gas/dimethyl-ether mode. Based on achieved results, carbon monoxide emission in natural gas/diesel mode is lower than 2 g/kW/h for all cases where this emission is higher than 8 g/kW/h in each case of natural gas/dimethyl-ether. This condition was also occurred for unburned hydrocarbons emissions, where this emission is higher than 11 g/kW/h for natural gas/dimethyl-ether fueling case while it is lower than 2 g/kW/h for natural gas/diesel mode. Quantitatively comparison shows that hydrogen addition is more effective on natural gas/dimethyl-ether reactivity controlled compression ignition mode. According to dimethyl-ether breaking up process, start of injection provides a time to decomposition of dimethyl-ether to its products, especially Methane. Based on numerical results, more than 10% of dimethyl-ether is broken up before start of combustion that represented importance of start of injection in natural gas/dimethyl-ether case.

Establishment of an improved heat transfer model based on an enhanced thermal wall function for internal combustion engines operated under different combustion modes

The heat transfer from the in-cylinder gases to the wall dramatically affects the combustion and emission characteristics of internal combustion engines, particularly for the engines operated with advanced low-temperature combustion modes. In the present work, an improved heat transfer model was established based on an enhanced thermal wall function using the piecewise functions, in which only the laminar Prandtl number is considered in the viscous sublayer, and the competition between the laminar Prandtl number and the turbulent Prandtl number is taken into account in the buffer layer and turbulent core regions. By implementing the improved heat transfer model into a computational fluid dynamics code, the predictions of the combustion processes and the heat transfer behaviors of an engine operated with conventional diesel combustion, homogeneous charge compression ignition, and reactivity controlled compression ignition modes were validated by the experimental data. Moreover, the computational results from two previous heat transfer models, i.e., Han and Reitz model and Rakopoulos et al. model, were presented for comparison. The results indicate that the heat flux characteristics under different combustion modes can be more satisfactorily reproduced using the improved heat transfer model than Han and Reitz model and Rakopoulos et al. model by avoiding the flaws in the thermal wall function. Finally, the influence of the dimensionless distance of the computational grid adjacent to the wall on the predicted heat flux was discussed to study the dependence of the heat transfer model on the size of the near-wall computational grid.

Experimental investigations to reduce unburned emissions in reactivity controlled compression ignition through fuel modifications

Reactivity Controlled Compression Ignition (RCCI) is a dual fuel LTC strategy wherein wider operating load range is achieved by utilizing low and high reactive fuels like gasoline and diesel, respectively. One of the major problems associated with RCCI is higher unburned emissions. The present work intends to reduce unburned emissions from RCCI combustion through fuel modifications. The investigated low and high reactive fuels include butanol- and ethanol-gasoline blends, gasoline-, butanol- and Karanja biodiesel-diesel blends. A production light duty diesel engine is modified to run in RCCI mode through suitable modifications. Based on PFI fuel sensitivity study, it is observed that 20% butanol and 80% gasoline blend (G80B20) results in lower HC, CO emissions and higher brake thermal efficiency. Similar results are obtained with 20% Karanja biodiesel and 80% diesel blend (D80K20) as the DI fuel. With G80B20 and D80K20 as PFI and DI fuels, respectively, the PFI to DI fuel ratio at each load conditions is optimized to further reduce unburned emissions in RCCI. Overall, it is concluded that by replacing gasoline and diesel with G80B20 and D80K20 as PFI and DI fuels, respectively, the HC and CO emissions are reduced by 50% along with 4.5% higher brake thermal efficiency.

Reactivity Controlled Compression Ignition combustion and emissions using n-butanol and methyl oleate

Direct Injection of methyl oleate and PFI of n-butanol were used to conduct Reactivity Controlled Compression Ignition (RCCI) and minimize exhaust emissions in reference to conventional diesel combustion. Methyl oleate was investigated for validation of a single fatty acid methyl ester as a surrogate for biodiesel in engine operation. An experimental common rail engine was operated in RCCI and conventional diesel combustion modes under constant boost and similar combustion phasing. The RCCI strategy used two pulses of direct injections with a fixed first injection at 60° before top dead center and a varied second injection for smooth combustion. Ringing intensity was reduced by 70% for methyl oleate RCCI compared to diesel conventional diesel combustion. The molecular oxygen from methyl oleate allowed a reduction in soot by 75% and 25% compared to diesel in RCCI and conventional diesel combustion operation, respectively. Compared to conventional diesel combustion, NOx and soot decreased for RCCI by several orders of magnitude with both emissions approaching near zero levels at low load. The fuels produced a stable RCCI operation where mechanical efficiency was sustained within 2% for same-load points and the coefficient of variation of indicated mean effective pressure was limited to 2.5%.

Investigation on performance and emissions of RCCI dual fuel combustion on diesel - bio diesel in a light duty engine

Reactivity Controlled Compression Ignition (RCCI) combustion has been established by modification of intake of a diesel engine. Studies were carried out on the existing engine with Conventional Diesel Combustion (CDC) and performance and emission parameters were recorded. Cotton seed biodiesel (COME) as low reactive fuel was injected into inlet manifold through a port fuel injector and diesel as high reactive fuel is injected in the cylinder through direct injection. Modified engine was tested for performance and emission characteristics. Simultaneous reduction in NOx and smoke emissions were observed with introduction of COME. CO2 emissions decreased marginally and unburnt hydrocarbons (UHC) decreased at lower percentages of COME and increased with higher percentages of COME. An increase in the Brake Thermal Efficiency (BTE) of the engine is observed at all loads. Exhaust Gas Temperature (EGT) and Brake Specific Fuel Consumption (BSFC) are lower in RCCI mode as compared to CDC. The optimum operating range of COME is observed with 10–20% of COME, which has 22% of average decrease in NOx and 30% decrease in the smoke emissions.

Reactivity controlled compression ignition and low temperature combustion of Fischer-Tropsch Fuel Blended with n-butanol

LTC was researched by introducing an 80% mass fraction of n-butanol in reactivity controlled compression ignition (RCCI) mode. A 60% mass fraction of n-butanol was port fuel injected (PFI) and the additional 20% was directly injected through a blend of n-butanol (Bu) with Fischer-Tropsch gas to liquid synthetic paraffinic kerosene (GTL) or ULSD as reference. The blended fuels GTL20-Bu80 and ULSD20-Bu80 have reduced cetane for improved combustion phasing control compared to the reference RCCI mode with direct injection of neat ULSD and n-Butanol PFI (ULSD40-Bu60). RCCI strategies delayed ignition and increased peak heat release rates due to prolonged mixing time and reactivity stratification, inducing faster flame speeds. In RCCI mode, the ringing intensity (RI) increased up to 85% higher than in CDC. NOx and soot were reduced up to 90% with ULSD40-Bu60 compared to CDC. The butanol blends decreased CO by 25% compared to ULSD RCCI. CO levels overlayed each other for GTL20-Bu80 and ULSD20-Bu80 across loads, suggesting that the butanol was the influencing factor. ULSD and ULSD20-Bu80 RCCI increased mechanical efficiencies compared to CDC by 3–4% across loads. ULSD20-Bu80 had the lowest cetane and displayed the greatest improvement in the overall emissions and efficiencies in RCCI compared to CDC.

A comparative study on partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI) in an optical engine

Partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI) are two new combustion modes in compression-ignition (CI) engines. However, the detailed in-cylinder ignition and flame development process in these two CI modes were not clearly understood. In the present study, firstly, the fuel stratification, ignition and flame development in PPC and RCCI were comparatively studied on a light-duty optical engine using multiple optical diagnostic techniques. The overall fuel reactivity (PRF number) and concentration (fuel-air equivalence ratio) were kept at 70 and 0.77 for both modes, respectively. Iso-octane and n-heptane were separately used in the port-injection (PI) and direct-injection (DI) for RCCI, while PRF70 fuel was introduced through direct-injection (DI) for PPC. The DI timing for both modes was fixed at –25°CA ATDC. Secondly, the combustion characteristics of PPC and RCCI with more premixed charge were explored by increasing the PI mass fraction for RCCI and using the split DI strategy for PPC. In the first part, results show that RCCI has shorter ignition delay than PPC due to the fuel reactivity stratification. The natural flame luminosity, formaldehyde and OH PLIF images prove that the flame front propagation in the early stage of PPC can be seen, while there is no distinct flame front propagation in RCCI. In the second part, the higher premixed ratio results in more auto-ignition sites and faster combustion rate for PPC. However, the higher premixed ratio reduces the combustion rate in RCCI mode and the flame front propagation can be clearly seen, the flame speed of which is similar to that in spark ignition engines but lower than that in PPC. It can be concluded that the ratio of flame front propagation and auto-ignition in RCCI and PPC can be modulated by the control over the fuel stratification degree through different fuel-injection strategies.

Experimental optimization of reactivity controlled compression ignition combustion in a light duty diesel engine

Reactivity Controlled Compression Ignition (RCCI) is emerging as a most promising combustion strategy to achieve near zero oxides of nitrogen (NOx) and smoke emissions along with higher brake thermal efficiency. The present work attempts to implement RCCI strategy in a production, light duty diesel engine by replacing an existing mechanical fuel injection with a flexible common rail direct injection diesel system and a low pressure gasoline port fuel injection system. Further, the engine compression ratio is reduced through modifications in piston bowl. Using a suitable controller, the engine operating parameters in terms of direct injected diesel timings, injection pressure, port injected gasoline quantity and gasoline to diesel ratio at each load conditions are optimized to achieve maximum brake thermal efficiency. Before modifications, the engine is run under conventional combustion mode at rated speed, varying loads to establish baseline reference data. The obtained results show that the engine could be operated in RCCI mode over its entire load range with a maximum increase of 14.2% brake thermal efficiency, near zero NOx and smoke emissions compared to conventional combustion. Further, reducing compression ratio is found to increase brake thermal efficiency by 7.6% and reduce carbon monoxide by 16.8% in RCCI.

Impact of oxygen enrichment on the engine's performance, emission and combustion behavior of a biofuel based reactivity controlled compression ignition engine

Diesel engine with RCCI (Reactivity Controlled Compression Ignition) finds the next generation technology in engine research for combusting slow burning fuels such as vegetable oils and arriving extremely lower levels of smoke and NO (Nitric Oxide) emissions simultaneously. An attempt was made to operate a diesel engine on RCCI mode by injecting ethanol as low reactivity fuel at the intake manifold of the engine using sunflower based Waste Cooking Oil (WCO) as high reactivity fuel under oxygen enriched intake air. The influence of the combined effect of oxygen enrichment and RCCI mode on engine's behavior was studied using WCO as the high reactivity (main) fuel. Significant improvement (upto 33.5% with RCCI mode from 29.1% with neat WCO at peak power) in BTE (brake thermal efficiency) with drastic reduction in smoke (upto 48% with RCCI at the maximum efficiency point from 69% with neat WCO at peak power) and NO were achieved with injection of ethanol under RCCI mode when using WCO as base fuel mainly at high loads (power outputs). Combining oxygen enrichment with RCCI resulted in further improvement in BTE (upto 36.2%) and reduction in smoke (upto 37% at the maximum efficiency point), HC and CO emissions at all power outputs. Peak pressure and energy release rate were found to be superior with RCCI mode with EF (electronic fuel) injection of ethanol associated with oxygen enriched combustion. It is concluded that RCCI operation with injection of ethanol combined with oxygen enrichment could be preferred for very high BTE, lowest smoke and NO emissions using WCO as base fuel. The optimal level of low reactivity fuel blending with high reactivity WCO could be at the ethanol energy share of 25% for the highest thermal efficiency at peak load. The optimal oxygen concentration of 23% by volume could be preferred for best performance of the engine fueled with WCO as main fuel.

Fuel consumption assessment of a multi-mode low temperature combustion engine as range extender for an electric vehicle

Low temperature combustion (LTC) engines, including homogeneous charge compression ignition (HCCI) and reactivity controlled compression ignition (RCCI), are promising to improve powertrain fuel consumption and reduce NOx and soot emissions by improving the in-cylinder combustion process. However, the narrow operating range of LTC engines limits the use of these engines in conventional powertrains. In range extenders, the engine is decoupled from the drivetrain, which allows the engine to operate in a limited operating range; thus, range extenders offer an ideal application for realizing the advantages of LTC engines. In this study, the optimum fuel consumption improvement of an experimentally developed 2-l multi-mode LTC-SI range extender is investigated in a light-duty battery electric vehicle (BEV) platform. In the optimization framework, the mode-switching fuel penalty, exhaust aftertreatment catalyst light-off temperature, and engine noise, vibration, harshness (NVH) are considered. The engine operation modes include HCCI, RCCI, and conventional spark ignition (SI). The simulation results show in the city driving cycle, the single-mode HCCI and RCCI range extenders offer 11.0% and 5.4% fuel consumption improvement, respectively over a single-mode SI range extender. These improvements increase to 12.1% and 9.1% in the highway driving cycles. In the multi-mode operation, up to 1.4% higher fuel economy is achieved over different driving cycles, compared to single-mode HCCI/RCCI operation. As the driving cycle average demanded power increases, the contribution of the RCCI mode predominates the HCCI mode.