Reactivity Controlled Compression Ignition Mode Research Articles

Comparative evaluation of combustion, performance, exergy and emission characteristics in hydrogen-biodiesel dual fuel engine under RCCI mode

The present work focuses on the impact of combustion phase shifting from CDC (conventional diesel combustion) to RCCI (reactivity controlled compression ignition) mode of operation under various premixed ratios of hydrogen on the combustion, performance and exhaust emissions of a partially modified CI (compression ignition) engine. The hydrogen premix ratios are varied from 10% to 60% with 10% increment and the engine is tested at 0.9 kW, 1.8 kW, and 2.7 kW. The experimental results have shown that the hydrogen participation up to 40% premixed ratio improves the homogeneousness and stability of the combustion, resulting in 8.19% increase in cylinder pressure and 27.81% increase in heat release rate (HRR) at 2.7 kW brake power. It is also observed that the premix phase of combustion is faster with up to 40% hydrogen participation as the 50% mass burn is found to shift towards TDC. At the same operating point, the combustion is also found to be more stable with 72% reduction in COVIMEP. The brake thermal efficiency (BTE) increases by 10.07% when operating at 2.7 kW brake power with a 40% premix ratio, compared to diesel CDC operation. The unburned hydrocarbon (UHC), carbon monoxide (CO), and PM emissions are reduced by 9.17%, 21.68%, and 9.51%, respectively, for the hydrogen premixed ratio of 40%, with a marginal increase in the oxide of nitrogen (NOX) emissions.

Comparative evaluation of conventional dual fuel, early pilot, and reactivity-controlled compression ignition modes in a natural gas-diesel dual-fuel engine

Comparative evaluation of conventional dual fuel, early pilot, and reactivity-controlled compression ignition modes in a natural gas-diesel dual-fuel engine

A Review on Recent Developments of RCCI Engines Operated with Alternative Fuels

Environmental concerns over automotive exhaust emissions and consumer demand for higher fuel efficiency have led to the development of low-temperature combustion concepts. The reactivity-controlled compression ignition (RCCI) engine is one among them and has the potential to reduce NOx and smoke emissions simultaneously. In this concept, a low-reactivity fuel is injected into the intake port and another high-reactivity fuel is injected into the cylinder directly. This results in reactivity stratification and provides more control over the rate of heat release. However, operating parameters such as reactivity of fuels, premixing ratio, injection strategies, exhaust gas recirculation ratio, piston bowl geometry, and compression ratio influence emissions formation. The article reviews recent developments on the effect of the above operating parameters on the performance and emission characteristics of RCCI engines operated with alternative fuels. The combustion strategies used to extend the RCCI mode to higher loads are also reviewed. Applications of computational fluid dynamics (CFDs) to design the combustion chamber for RCCI engines are discussed. The need for further improvements in the CFD models for RCCI engines is explained. After presenting a thorough review of recent literature, directions for future research on RCCI engines are proposed.

Numerical investigation of natural gas (NG) as low reactivity fuel in a reactivity controlled compression ignition (RCCI) engine model

Natural Gas (NG) with its high octane number and low C/H ratio is beneficial for reactivity controlled compression ignition (RCCI) engines in controlling the rate of pressure rise and lower the emissions, given that these engines still suffer from these two problems. Therefore, in this study, a detailed 3D combustion model was developed in ANSYS-Forte environment on the scanned image of a real single-cylinder diesel engine for the application of NG to RCCI engines and then validated with the experimental data of the same engine. Afterward, the effect of NG premixed ratio (Rp, 15%, 30% and 45%) on the combustion and emission characteristics of the RCCI engine were analyzed at 20% load and 2400 rpm. Results showed that by increasing the Rp, the heat release rate and cylinder pressure decreased while the ignition delay (ID) period increased. Moreover, NOx and HC emissions were observed to be increased whereas CO and C2H2 emissions tended to be declined as Rp increased. CO emissions were decreased up to 29% when RCCI mode was applied. Also, C2H2 emissions were reduced by about 97% by RCCI compared to CDM. However, engine efficiency started to decrease as Rp increased.

The influence of different fuels and injection methods of RCCI and DCI in hybrid ICE-Battery vehicle performance

The incorporation of two recent technologies of using the dual-fuel reactivity controlled compression ignition (RCCI) combustion engine within the hybrid electric vehicle (HEV) is practiced to show how this combination can reduce the emission and enhance the thermal efficiency of the system. In particular, the heat transfers from the engine wall and the exhaust heat flow from the engine under different injection modes and fuels are of interest. The study in terms of thermal performance, fuel consumption, and battery state of charge (SOC) focuses mainly on the comparison between three cases of D100 (pure diesel) as the reference (baseline conventional direct pure diesel injection) case, D80H20 (80% diesel, 20% hydrogen) direct co-injection (DCI), and D80H20 RCCI (port + direct dual fuel injection). The NOx emission and engine power in the simulated drive cycle are investigated where the battery capacity and D50M50 (direct co-injection of 50% diesel with 50% methanol) are the additional cases. The findings indicate that the Battery SOC is preserved in better condition when the RCCI mode engine is coupled in the hybrid vehicle. The piston wall heat flux for D80H20 in DCI increases by 45.2% and for the RCCI increases by 60.5% compared to baseline diesel injection mode. It is also proved that the HEV releases considerably lower NOx compared to DCI and more NOx compared to D100 and D50M50.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.

Effect of pilot injection strategy on the methanol-mineral diesel fueled reactivity controlled compression ignition combustion engine

Amongst all low-temperature combustion (LTC) strategies, reactivity-controlled compression ignition (RCCI) combustion garners more debate from researchers because of its excellent combustion and performance characteristics and lower emissions over a wide operating range. In this experimental investigation, the consequences of the start of diesel injection (SoIdiesel) timing using different pilot injection techniques, such as single and double pilot injection (SPI and DPI, respectively), have been investigated. Tests were performed at a fixed engine speed and load (1500 rpm and 3 bar BMEP, respectively) using different premixed ratios (rp: 0, 0.25, 0.50, and 0.75) of methanol on an energy basis. Experimental results indicated that the start of combustion (SoC) and combustion phasing (CP) advanced with advancing SoIdiesel. However, too advanced and retarded SoIdiesel timings resulted in combustion noise and misfire. The use of pilot injection was found suitable for the RCCI mode, especially at lower rp. However, SPI and DPI strategies didn’t show significant variations in the combustion characteristics. Exhaust gas temperature (EGT) showed a random trend with SoIdiesel timing, and it decreased with the increasing number of pilot injections. RCCI mode produced higher hydrocarbon (HC) and carbon monoxide (CO) and lower oxides of nitrogen (NOx) emissions. All these gaseous emissions decreased with advancing the SoIdiesel. Particulate matter (PM) analysis showed that the RCCI mode emitted relatively lower PM than the baseline CI mode, further reducing with increased methanol fuelling. PM emissions also decreased by retarding SoIdiesel, in which reduction in smaller particles was dominant. The analysis of critical parameters such as brake thermal efficiency (BTE), HC, NOx, and PM emissions suggested that the optimum rp of methanol and suitable injection strategy can significantly improve the combustion, performance, and emissions characteristics of the RCCI mode.

Enhancement of energy conversion and emission reduction of Calophyllum inophyllum biodiesel in diesel engine using reactivity controlled compression ignition strategy and TOPSIS optimization

The present investigation mainly focuses on the abatement of NOx and soot emissions and enhancing the performance of the CI (Compression Ignition) engine through RCCI (Reactivity Controlled Compression Ignition) strategy with low reactive gasoline as an inducted fuel. The high reactive biodiesel extracted from Calophyllum inophyllum feedstock was an ignition source of RCCI combustion. Investigational results have revealed that combustion of RCCI has shown an enhancement of about 0.2–1.2%, 4.9–13.6%, and 11.3–44.6% for Brake Thermal Efficiency (BTE), maximum in-cylinder combustion pressure (Pmax), and Net Heat Release Rate (NHRR), respectively at full load when compared to biodiesel blends. Similarly, RCCI strategy significantly reduces the emissions of NOx and soot by 24.40–43.74% and 31.28%–52.57% respectively at maximum loads. On the other hand, emissions of CO and HC are higher than the biodiesel at all loads. However, an upsurge in gasoline injection from 3 ms to 5 ms in RCCI mode decreases Pmax, NHRR, BTE, and NOx and soot emissions. This is mainly attributed to the superior cooling effect of gasoline and longer ignition delay. Multi-response optimization is performed with TOPSIS, B10 + 3 ms GF, and 100% load is identified as an optimal operating condition.

Experimental study on combustion characteristics of a fischer‐tropsch diesel/methanol reactivity controlled compression ignition mode engine

AbstractF‐T diesel is an alternative fuel with a high cetane number (CN) for internal combustion engines. Methanol has a low CN and contains oxygen. F‐T diesel and methanol are potential fuels for the reactivity controlled compression ignition (RCCI) engines. In a single‐cylinder 186FA compression‐ignition engine with a combination of methanol inlet pipe injection and F‐T diesel in‐cylinder injection, the combustion characteristics of the F‐T diesel/methanol RCCI mode engine are investigated. The results show that as methanol premixed ratio (MPR) increases, the ignition delay (ID) is prolonged at low load conditions, the maximum in‐cylinder pressure (Pmax) and indicated thermal efficiency (ITE) a decreased. When the MPR increases from 0% to 60%, the ID is extended by 1.7°CA, the Pmax decreases by 8.1%, and the ITE decreases by 1.1%. At high load conditions, MPR rises from 0% to 60%, combustion duration (CD) is shortened by 2.4°CA, Pmax is increased by 8.3%, and the ITE is increased by 1.7%. The fuel injection advance angle (IAA) of F‐T diesel significantly influences the combustion process of the RCCI engine. As the IAA increases, the ID is shortened at high loads, and the Pmax and the ITE are increased. When the MPR is 60% and the IAA is 14°CA, the ITE of the engine is increased by 2.04%, and the equivalent indicated fuel consumption rate(be) is reduced by 5.68% compared with the engine fueled with F‐T diesel under high loads.

Simulation study on effects of EGR ratio and compression ratio on combustion and emission characteristics of PODE/methanol RCCI engine

In order to solve the problems of combustion instability and emission deterioration of reactivity controlled compression ignition (RCCI) engine under high load, the in-cylinder combustion model of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel RCCI engine was constructed by CONVERGE software coupling with chemical reaction mechanism, and the influence mechanism of exhaust gas recirculation (EGR) ratio and compression ratio (CR) on engine performance, in-cylinder combustion and emission characteristics of PODE/methanol RCCI mode was systematically studied. Results show that with the increase of EGR ratio, the combustion phase of RCCI mode is gradually delayed, the ignition delay and combustion duration are extended, the CA50 phase is gradually delayed, the combustion temperature decreases, the mixture distribution becomes more uniform, and the combustion process becomes smoother. When the EGR ratio increases from 0 % to 30 %, NOx production is reduced by 47.3 %, ringing intensity (RI) and maximum pressure rise rate (MPRR) decreases by 1.31 MW/m2 and 0.37 MPa/°CA respectively, and brake thermal efficiency (BTE) decreases from 45.45 % to 43.19 %. With the reduction of CR, the combustion start point is gradually postponed, the peak heat release rate and combustion temperature continuously decrease, and both IMEP and BTE show a downward trend. The variation of CR breaks the trade-off relationship between NOx and soot, and improves combustion stability, but it is also limited by the BTE reduction. When the CR decreases from 17.5 to 15.5, NOx and soot production are reduced by 28.58 % and 20.1 %, RI and MPRR are reduced by 1.26 MW/m2 and 0.7 MPa/°CA respectively, and BTE decreases from 45.45 % to 44.52 %. Therefore, the CR of 16.5 is more suitable for stable operation of PODE/methanol dual-fuel RCCI engine at high load.

Thermofluids analysis of combustion, emissions, and energy in a biodiesel (C11H22O2) / natural gas heavy-duty engine with RCCI mode (Part I: Single/ two -stage injection)

• The effects of fuel injection strategy for using the concept of RCCI combustion in a heavy-duty biodiesel engine have been investigated. • For the first time in a heavy-duty biodiesel engine, biodiesel fuel (C 11 H 22 O 2 ) as a new fuel has been used in this level. • Changing the high reactivity fuel injection time from -40° to -60°, the rate of heat released decreases but output power increases. • The mass of HC and CO pollutants has drastically decreased with the onset of injection earlier. One of the novel methodologies used to increase energy efficiency and reduction of environmental pollutants in internal combustion engines is the idea of low-temperature combustion (LTC) especially reactivity controlled compression ignition (RCCI). Given that the ultimate goal of RCCI combustion is combustion controllability through in-cylinder reactivity stratification by using two different fuels, there are many modifiable factors, which can be improved or adjusted. The aim of this research is to use the concept of RCCI combustion in a biodiesel (C 11 H 22 O 2 ) / natural gas heavy-duty engine and the performance and amount of pollutants of engine output is evaluated and compared by modifying the input parameters (different fuel injection strategy). Accordingly, numerical simulations have been carried out to study combustion in the geometry of the Caterpillar 3401E engine with CONVERGE computational fluid dynamic software and the SAGE combustion model. Results show that: By changing the biodiesel injection time (from -40° to -60°), although, the rate of heat released decreases, output work and Indicated mean effective pressure (IMEP) increase. By increasing the lag of time between the first and second injections (in Cases 1–3), the IMEP will increase from 6.9 to 8.2 bar and the work from 1686 to 1997 J. In Cases (7–9), the mass of HC and CO pollutants has drastically decreased with the onset of injection earlier, whereas the mass of NOx pollutants has increased.

Closed-Loop Predictive Control of a Multi-mode Engine Including Homogeneous Charge Compression Ignition, Partially Premixed Charge Compression Ignition, and Reactivity Controlled Compression Ignition Modes

Closed-Loop Predictive Control of a Multi-mode Engine Including Homogeneous Charge Compression Ignition, Partially Premixed Charge Compression Ignition, and Reactivity Controlled Compression Ignition Modes

Experimental studies on premixed charge and reactivity-controlled compression ignition combustion modes using gasoline/diesel fuel combination

Homogeneous charge compression ignition (HCCI) is a promising technology to reduce NOx and soot emissions in compression ignition (CI) engines. However, this technology lacks combustion control to circumvent the knocking and misfire limitations. Premixed charge compression ignition (PCCI) and reactivity-controlled compression ignition (RCCI) are techniques that use partial homogeneous charge to reduce NOx and soot emissions. Here, combustion is regulated either by controlling the injection timing or fuel reactivity. PCCI uses a part of fuel as premixed to form a partially homogeneous charge and the rest as direct-injected. RCCI, on the other hand, uses a low reactive fuel (LRF) for port injection to form a partially homogeneous charge and a high reactive fuel (HRF) for direct injection. In this work, we studied PCCI and RCCI modes using commercially available fuels like diesel and gasoline, and we compared the results with diesel baseline operation. Adding 40% (by weight) heated diesel port injection to normal diesel operation in PCCI mode at different loads showed a minimum reduction in NOx and smoke emissions by 15% and 6%, respectively, when compared with diesel baseline. This mode was found to be equally efficient with diesel baseline operation at low torque conditions. Similarly, adding 40% (by weight) of gasoline port injection to normal diesel operation in RCCI mode at different loads showed a minimum reduction in NOx and smoke emissions by 20% and 14%, respectively, when compared with diesel baseline. This mode was found to be equally efficient with diesel baseline operation at high torque conditions.

Effect of manifold injection of 1‐hexanol on a reactivity controlled compression ignition engine fuelled with neem oil methyl ester blend

AbstractThe novelty of this research aims to attain low‐temperature combustion with the help of reactivity controlled compression ignition (RCCI) in a single cylinder, four‐stroke diesel engine by premixing the low reactivity fuel (LRF) such as 1‐hexanol with air in the intake manifold along with high reactivity fuel (HRF) such as neem oil methyl ester in the volumetric ratio of 80:20 (B20) as a primary fuel. HRF has been utilized as a primary fuel through the main injector along with the manifold injection of LRF fuel through a secondary injector at various energy shares, such as 10%, 20%, 30%, and 40%, and the fuel combinations were designated as B20HI10, B20HI20, B20HI30, and B20HI40. The readings were noted from no load to full load and the experiment showed that the brake thermal efficiency (BTE) was increased in RCCI mode up to 30% 1‐hexanol share compared with B20 due to its better combustion, which was evident by higher heat release rate (HRR); beyond 30%, there was a drop in BTE due to the reduction in pilot fuel quantity. Oxides of nitrogen and smoke were significantly reduced for all combinations in RCCI mode, whereas hydrocarbon and carbon monoxide emissions were increased substantially. A substantial increase in peak pressure and HRR was noticed in RCCI mode compared with conventional mode due to its better homogeneity and prolonged ignition delay. From the findings, this research suggests that B20‐1‐hexanol combinations in RCCI mode can be an attractive replacement for diesel fuel.

Methane slip reduction of conventional dual-fuel natural gas diesel engine using direct fuel injection management and alternative combustion modes

Alternative combustion mode and change of spray geometry show potential for methane slip reduction in a dual fuel diesel-natural gas internal combustion engine. Three combustion regimes are simulated; a conventional diesel methane dual-fuel combustion and two modes of reactivity controlled compression ignition (RCCI) with early (EIRCCI) and late (LIRCCI) injections. Methane is injected as the premixed fuel into the port and diesel as direct-injected fuel in all combustion modes. The start of direct fuel injection (SOI) is used as the combustion management tool, swiping from misfiring to knock limits at part loads.By switching combustion mode from conventional (CDF) to LIRCCI and EIRCCI, methane slip is reduced by 12% and 33%, respectively. SOI is used effectively to manage methane slip in any combustion mode, but the effect is more substantial in the EIRCCI mode.Emission results support methane slip trends’ observations. Nitrogen oxides (NOx) emission is increased in CDF by advancing SOI and decreased in both the LIRCCI and EIRCCI modes. Compared to CDF, late and early injection RCCI modes produce 417% and 67% more soot. Also, results show that high levels of methane slip in CDF can be reduced to some extent without any geometry modification by SOI management.Three diesel spray angles (SAs) of 60, 90, 120° are examined. Minimum methane slip is obtained when the SA is towards the squish area, and maximum methane slip is obtained when the SA is towards the piston bowl. Increasing SA from 60 to 90 and 120° results in a 16.4% and 42.5% reduction of methane slip.

Experimental study on reduction of pollutant emissions in reactivity controlled compression ignition (RCCI) engine fueled with diesel/gasoline fuels

Reactivity Controlled Compression-Ignition (RCCI) concept presents a great potential to reduce both NOx and soot emissions from conventional diesel engines with improved thermal efficiency. Therefore, in this work, a single-cylinder diesel engine with CRDI was operated on RCCI mode. To investigate the effect of RCCI mode on engine performance and emissions, gasoline was injected into the port as LRF, while diesel was injected directly into the cylinder as HRF. Premixed ratio of low reactivity fuel was varied from 0% (conventional diesel mode, CDM) to 60% with 15% intervals as energy ratio given to engine per cycle. Engine load was also studied from 20% to 60% of max. engine torque with 20% intervals to stimulate low, mid and mid-high load conditions. Experimental results showed that with increase of Rp, unburned HC and CO emissions increased while smoke opacity decreased significantly (up to about 95% in case of 0.60 Rp and 60% engine load) in gasoline/diesel RCCI compared to CDM. Though NOx emissions decreased at low engine loads with RCCI strategy, they started to increase with increase of Rp at high loads.

Numerical Study of the Effects of Lambda and Injection Timing on RCCI Combustion Mode

Reactivity Controlled Compression Ignition (RCCI), which is a low temperature combustion mode based on the principle of working with dual fuel, has attracted the attention of researchers in recent years due to its advantages such as high thermal efficiency, low NOx and soot emissions, and controllability of combustion. In this study, the effects of injection timing and lambda on RCCI combustion mode were investigated numerically by validating the experimental data with Converge CFD software. A four-cylinder, four-stroke gasoline direct-injection engine with a compression ratio of 9.2 was used in RCCI combustion mode at an engine speed of 1000 rpm. The maximum cylinder pressure also increased and RCCI combustion was advanced while the injection timing was advanced. The highest peak pressure was obtained at SOI=-50°CA aTDC, and the lowest peak pressure was obtained at SOI=-25°CA aTDC. Similarly, the highest peak HRR value was acquired as 213 J/°CA at SOI=-50°CA aTDC. It has been observed that as the lambda decreases, the maximum cylinder pressure increases, and combustion advances. In addition, the heat release rises with a decrease in lambda value. The maximum heat release rate was acquired as 77.91 J/°CA at λ=1.2. The results show that injection timing and lambda have a great influence on RCCI combustion mode and the combustion phase can be controlled with these parameters.

Experimental investigation into the effects of pilot fuel and intake condition on combustion and emission characteristics of RCCI engine

Due to the excellent physicochemical properties, coal to liquid (CTL) is suitable for use as an alternative fuel in internal combustion engines. It is conducive to promoting efficient and clean utilization of coal. In this study, the experiment of using CTL and conventional diesel as pilot fuel and gasoline as the premixed fuel was carried out on a modified dual-fuel engine. The combustion boundary conditions, including gasoline ratio, intake flow rate, and intake temperature, were modulated at an engine speed of 1400 rpm and under low load. The combustion parameters and emission characteristics were fully discussed. The results show that both gasoline/CTL reactivity controlled compression ignition (RCCI) mode and gasoline/diesel RCCI mode contain low temperature heat release (LTHR) and high temperature heat release (HTHR) phases. Among them, the gasoline/CTL RCCI mode has a higher proportion of LTHR, and the low-temperature combustion occurs later than gasoline/diesel. Besides, the ignition delay (ID) of gasoline/CTL RCCI mode is generally shorter, and CA50 is more forward than that of gasoline/diesel RCCI. Compared with gasoline/diesel RCCI mode, the intake air flow has a more significant effect on the indicated thermal efficiency (ITE) and particle emissions of gasoline/CTL RCCI. In particular, the problem of high accumulation mode particles brought by the CTL can be solved by appropriately increasing the intake flow rate. There is an optimal intake temperature for the ITE of gasoline/CTL RCCI mode, while the ITE of gasoline/CTL RCCI mode remains almost constant as the intake temperature increases. Compared with diesel, when using high cetane number (CN) CTL as a pilot fuel, the combustion is more stable, and the ITE of that at each operating condition is about 3% higher. Under optimum intake conditions, the gasoline/CTL RCCI mode achieves higher thermal efficiency and products lower CO, HC, and particle emissions, but NOx emissions increase slightly.

Comparison of ethanol/diesel fuel dual direct injection (DI2) strategy with reactivity controlled compression ignition (RCCI) in a diesel research engine

The dual direct injection (DI2) strategy is expected to cover the advantages of conventional diesel (CDI) mode while avoiding deficiencies of reactivity controlled compression ignition (RCCI) strategy such as high amount of incomplete combustion emissions and extremely high rate of pressure rise. Therefore, the present study focused on the comparison of combustion characteristics of these combustion modes in a diesel research engine, which was firstly operated under CDI mode at varying loadings and a constant speed of 2400 rpm to establish the reference data. Then, a low pressure port fuel injection (PFI) and high pressure gasoline direct injection (GDI) systems were activated to run on RCCI and DI2 modes, respectively, whereas test engine was already equipped with a common-rail direct injection (CRDI) system for conventional diesel fuel injection. Results showed that both direct and port injection methods increased the in-cylinder pressure (up to 9%) compared to conventional mode. In RCCI combustion, the rate of pressure rise increased more than direct injection and conventional mode. CDI exhibited higher thermal efficiency than RCCI and DI2 modes while both advanced modes were successful in reducing NOx and Smoke Opacity. However, significantly higher CO and unburned HC emissions were observed with both advanced modes in comparison to conventional one. Both CO and unburned HC emissions were reduced by direct injection of ethanol (DI2 strategy) at the rates of 16% and 35% compared with port injection method of RCCI strategy. This is an important finding of this study, which shows that the DI2 strategy has a potential to address a deficiency of RCCI and will bring it closer to its application to practical engines.

Experimental investigation on combustion and emission characteristics of reactivity controlled compression ignition engine powered with iso-propanol/biodiesel blends

Recently, reactivity controlled compression ignition (RCCI) has been proposed in order to achieve a higher thermal efficiency with lower emissions than conventional combustion. In RCCI mode, as the fuel types and their combinations affects the reactivity stratification inside cylinder, thus combustion control, in present study, iso-propanol was evaluated as low-reactivity fuel (LRF) when petroleum diesel, commercial biodiesel and their blends were high-reactivity fuels. It is of great importance that iso-propanol and biodiesel be used together in RCCI mode, as they significantly affect the in-cylinder stratification due to their high octane/cetane number. Therefore, the reactivity controlled compression ignition (RCCI) combustion characteristics was investigated in a diesel research engine using iso-propanol, petroleum diesel, biodiesel and their blends as fuels. Tests were conducted on varying loadings (from 20% to 60% of max torque) and premixed ratios of LRF (Rp = 0, 0.15, 0.30, 0.45, and 0.60) at a constant engine speed of 2400 rpm. Results, which were compared with conventional diesel combustion (CDC), showed that, as the premixed ratio (Rp) of low-reactivity fuel (iso-propanol) increased, ignition delay (ID) period prolonged while combustion duration (CD) and rate of pressure rise (RoPR) reduced assisted to reduce NO emissions and smoke opacity in the exhaust. NO and smoke opacity reduced simultaneously for biodiesel-propanol combinations up to 40% under 20% load and 0.60 premixed ratio of LRF compared to CDC. Propanol premixed ratio of 0.30 at 60% load was found to be optimum concerning lowest emissions. In conventional mode, HC emissions reduced by up to 52% when biodiesel and its blends with diesel fuel are used, whereas they increased significantly in RCCI mode. According to overall results, it is concluded that RCCI performed better than CDC at entire load.