Browse Topic: PCCI engines
The end-gas auto-ignition and associated pressure wave generation in a premixed gas with a spatial distribution is numerically investigated. This study assumes that the auto-ignition phenomenon in the end-gas of PCCI combustion, a next-generation combustion method which is expected to achieve both low fuel consumption and low emissions at a high level. Detailed numerical analysis considering the chemical kinetics on the one-dimensional compressible fluid flow with high spatial and time resolution was performed to clarify the detailed phenomena of the auto-ignition and onset of the pressure wave and its propagation in the end-gas. Followings are results. (1) The pressure wave generations related with the auto-ignition in the end-gas is categorized into two types. The cases that the auto-ignition velocity, which is the localized auto-ignitive propagation velocity relative to the unburned mixture, exceeded the local sound speed, or not. The spatial distribution of the equivalence ratio in the initial unburned mixture affects the auto-ignition velocity. (2) In the cases that the Mach number of the auto-ignition velocity was less than one, the intensity of the pressure wave associated with the auto-ignition is relatively small, and the pressure wave propagates quietly with sound speed. (3) On the other hand, in the cases that the Mach number of the auto-ignition velocity exceeded one, very strong pressure wave is initiated by the auto-ignition. The temperature rise due to the auto-ignition and the pressure rise propagates synchronously toward the unburned mixture.
Letter from the Special Issue Editors
Premixed Charge Compression Ignition (PCCI) is a promising LTC strategy to reduce NOx and soot emissions without relying on after-treatment devices. One major drawback of PCCI is high HC and CO emissions resulting from fuel-wall impingement due to early injection of diesel. Narrow-angle direct injection (NADI) helps reduce the wall wetting of fuel. But it is effective only at lower loads. At mid and higher loads, it increases soot and CO emissions in small-bore engines due to the formation of fuel-rich pockets in the piston bowl region. This problem is addressed using a split injection strategy in the present work. A 3-D CFD model is developed and validated with experimental data at two load conditions. Simulations are performed using CONVERGE CFD software. Split injection strategies are explored using wide (148 deg) and narrow (88 deg) spray included angles. The investigations concluded that a main injection of 20 deg bTDC and 30 deg bTDC were optimal for wide and narrow spray included angles, respectively. For both cases, a dwell time of 15 deg CA was optimal. Compared to single injection, split injection resulted in 2% and 4% improvement in indicated thermal efficiency for wide and narrow-angle, respectively. Split injection results in a reduction of 83% and 80% in CO, 56% and 64% in soot and 48% and 60% in HC emissions for wide and narrow included angle respectively when compared with single-injection NADI-PCCI combustion.
Premixed charged compression ignition (PCCI) is a promising low temperature combustion strategy for achieving a simultaneous reduction of oxides of nitrogen (NOx) and soot emissions in diesel engines. However, early direct injection results in a significant penalty in fuel economy, high unburned hydrocarbon (HC), and carbon monoxide (CO) emissions, especially in small-bore diesel engines. In the present work, computational fluid dynamic (CFD) investigations are carried out in a small-bore diesel engine using a commercial CFD software, CONVERGE. The computational models are validated with experimental results at two different load conditions, 20% and 40% of rated load. The validated models are used to carry out parametric investigations on the effects of fuel injection parameters, namely the start of fuel injection timing, injection pressure, and spray cone angle on PCCI combustion. The fuel-air equivalence ratio, temperature, and emission contours are used to get more insight into the effect of fuel injection parameters on the combustion process to reduce the spray wall wetting and the high HC and CO emissions. The results obtained show reduced NOx and soot emissions with advanced injection timings from 20 deg to 50 deg. CA bTDC with a penalty on the HC and CO emissions and the indicated thermal efficiency. Increasing injection pressure from 300 to 900 bar resulted in higher HC and CO emissions at both loads due to increased spray wall impingement. A narrow spray cone angle of 88 deg. results in a significant reduction in the HC and CO emissions by up to 77% and 80%, respectively, compared to a wider cone angle of 148 deg. at low load condition. At high load, using a narrow spray angle resulted in an increase in the CO and soot emissions with only a minor reduction in HC emissions due to poor air utilization in the current small-bore engine.
Increasing regulatory demand to reduce CO2 emissions has led to a focus on advanced combustion strategy development to improve overall engine efficiency. Gasoline compression ignition (GCI) has been demonstrated by others to have the potential to meet future CO2 regulations and emissions while achieving comparable to better efficiency than conventional diesel compression ignition (DCI). Soot and NOx emissions are also reduced significantly by using gasoline instead of diesel in compression ignition engines due to differences in composition, fuel properties, and reactivity. In comparison with diesel fuel, gasoline has a higher volatility and more resistance to autoignition, therefore, its longer ignition delay time will allow for better mixing of the air-fuel charge before combustion. In this study, a GCI combustion system has been tested in a Hyundai 2.2L engine as part of a US Department of Energy funded project. A double-injection strategy was tested from mid-to-high loads (5-20 bar BMEP) and for engine speeds in the range of 1200-3000 rpm. Up to 43.4% brake thermal efficiency was achieved using the GCI mode versus 41% using DCI mode. The GCI mode has demonstrated two distinct strategies that work at different load ranges, partially premixed compression ignition (PPCI) and mixing-controlled compression ignition (MCCI). Overall, this study shows that for similar engine-out NOx levels, GCI mode had higher brake thermal efficiency than DCI with lower fuel pressure and EGR required.
Diesel vehicle market have been recognized the need for change. In order to meet the strengthened emission regulations, innovative combustion technologies that can maintain power and improve fuel efficiency are becoming important solutions for diesel engines. This study deals with the goal of homogeneous combustion formation through changes in injection angle of conventional diesel engines. The conventional diesel engines show local combustion and has the limitation of generating exhaust gas including wall wetting phenomena. On the other hand, the appropriate injection angle optimization for the piston bowl shape can reduce wall wetting and form a homogeneous mixture overall in combustion. This study used 1D thermodynamic simulation to validate the conventional 4-cylinder diesel engine and compared to the test results to obtain modeling accuracy. To describe combustion behavior under 1D environment, multi-injection was used to increase the mixing time between air and fuel, which increases the temperature inside the cylinder, evaporates the fuel and creates a in-cylinder mixture and combustion processes. Secondly, detailed combustion analysis was performed using 3D CFD for spray combustion by creating a homogeneous mixture with change in injection angle, and the detailed combustion behavior was visualized. As a result, the optimized injection can provide enhanced egg motion, and optimal Heat Release Rate (HRR) can cause the soot to oxidize. Also optimized injection angles that can reduce the wall wetting were predicted to prevent incomplete combustion by forming homogeneous mixture. The emission results from homogenous mixture confirmed that nitrogen oxide (NOx) and particulate matter(PM) were reduced after combustion, and the results of unburned hydrocarbon(UHC) and carbon monoxide(CO) were confirmed by varying injection angle with reduced wall wetting. This can meet the premixed charge compression ignition (PCCI) by reducing emissions of NOx and PM. Furthermore, changing the injection angle for complete combustion can be an indicator for small diesel engines by connecting with early injection strategies, which is our future work scope.
Achieving stable combustion without misfire and knocking is challenging in premixed charge compression ignition (PCCI) especially in small bore, air cooled diesel engines owing to lower power output and inefficient cooling system. In the present study, a single cylinder, air cooled diesel engine used for agricultural water pumping applications is modified to run in PCCI mode by replacing an existing mechanical fuel injection system with a flexible common rail direct injection system. An advanced start of fuel injection (SOI) and exhaust gas recirculation (EGR) are required to achieve PCCI in the test engine. Parametric investigations on SOI, EGR and fuel injection pressure are carried out to identify optimum parameters for achieving maximum brake thermal efficiency. An SOI sweep of 12 to 50 deg. CA bTDC is done and for each SOI, EGR is varied from 0 to 50% to identify maximum efficiency points. It was found that EGR helps in extending the load range from 20 to 40% of rated load. However, it resulted in increase in unburned hydrocarbon (HC) emissions. To study the effect of injection pressure, SOI, speed and EGR rate were fixed as constant and injection pressure was varied from 300 to 900 bar. Unlike conventional combustion, increasing fuel injection pressure is not beneficial in PCCI in the present small-bore engine wherein significant increase in HC, carbon monoxide (CO) and smoke emissions is observed which could be due to spray wall impingement. It was observed that increasing fuel injection pressure increased the efficiency only slightly whereas the penalty in terms of HC and CO emissions were significant. Based on the results obtained, it is concluded that for achieving PCCI in the present small-bore engine, an early fuel injection with high EGR and lower injection pressures are required.
Partially premixed combustion (PPC) is a promising way to achieve high thermal efficiency and low emissions, especially by using multiple injection strategies. The mechanisms behind PPC efficiency are still to be explained and explored. In this paper, multiple injections have been used to affect the gross indicated efficiency in an optical PPC engine modified from a Volvo MD13 heavy-duty diesel engine. The aim is both to improve and impair the gross indicated efficiency to understand the differences. The combustion natural luminosity is captured by a high-speed camera, and the distribution of fuel, oxygen, and temperature during the combustion process has been further explored by CFD simulation. The results show that with the right combination of the pilot, main, and post injection the gross indicated efficiency can be improved. Using a post injection in a triple-injection case show to have less effect on the combustion phasing than pilot injection in a double-injection case, while it can significantly affect combustion efficiency. The later of the double-injection cases tested (c30/16), has less heat transfer losses since the high-temperature region transported away from the cylinder head and piston bowl wall, which can be seen in the CFD-simulations. The highest gross indicated efficiency among the tested cases is given by the triple-injection case d38/24/6 as it reaches the best balance between the mixing and the local temperature through the jet-jet interactions and combustion-jet interactions.
Premixed charge compression ignition (PCCI) combustion is effective in reducing harmful exhaust gas and improving the fuel consumption of diesel engines [1]. However, PCCI combustion has a problem of exhibiting lower combustion stability than diffusive combustion [2, 3], which makes it challenging to apply to mass production engines. Its low combustion stability problem can be overcome by implementing complicated injection control strategies that account for variations in environmental and engine operating conditions as well as transient engine conditions, such as turbocharging delay, exhaust gas recirculation (EGR) delay, and intake air temperature delay. Although there is an example where the combustion mode is switched according to the intake O2 fraction [4], it requires a significant number of engineering-hours to calibrate multiple combustion modes. And besides, such switching combustion modes tends to have a risk of discontinuous combustion noise and torque. In this study, a physical model of PCCI combustion is developed and applied to calculate the cycle-by-cycle ignitability of the cylinder to control the ignition delay, thereby eliminating the need for switching multiple combustion modes. Applying continuous control improves the combustion reliability where the target ignition delay is continuously updated by the physical model’s ignitability calculation. The lower the ignitability, the longer the target ignition delay, and the higher the ignitability, the shorter the target ignition delay. As a result, it was demonstrated that even if there are variations in the intake and transient engine conditions, consistent and stable rate of heat release (ROHR) can be achieved.
The objective of this study was to investigate combined effects of split injection strategies and intake air humidification on combustion and emissions of a partially premixed charge compression ignition (PCCI) marine diesel engine. In this research, a three-dimensional numerical model was established by a commercial code AVL-Fire to explore in-cylinder combustion process and pollutant formation factors in a four-stoke supercharged intercooled marine diesel engine under partial load at 1350 r/min. The novelty of this study is to combine different water-fuel ratios and fuel injection parameters (pilot injection timing and main injection timing) to find the optimized way to improve engine performance as well as NOx-soot emissions, thus meeting the increasingly stringent emissions restriction. The results indicate that as the main injection timing advances (-14°CA to -20°CA aTDC), the in-cylinder peak pressure increases by about 10%, the main injection ignition delay (MI ignition delay) becomes longer, the CA50 is advanced near the top dead center (TDC), which is effective to improve the indicated thermal efficiency (ITE). Meanwhile, soot emissions are reduced by about 50% compared with the original engine at the -20°CA aTDC main injection timing. The early pilot injection timing can form relatively uniform temperature field and concentration field in the cylinder before the start of main injection (SOMI) timing, which is advantageous to fuel-air mixing. The high level of water-fuel ratio is utilized to reduce overall combustion temperatures and achieve low temperature combustion of the diesel engine. NOx emissions significantly decrease by about 75% compared with the original engine when the water-fuel mass ratio is 2.0. All in all, the technical route to improve the NOx-soot trade-off relationship is found through the coupling optimization of split injection strategies and intake air humidification. Meanwhile, the indicated specific fuel consumption (ISFC) is reduced and NOx-ISFC trade-off relationship is improved.
The partially premixed combustion (PPC) concept is regarded as an intermediate process between the thoroughly mixed Homogeneous charge compression ignition (HCCI) combustion and compression ignition (CI) combustion. It’s a combination of auto-ignition mode, a fuel-rich premixed combustion mode, and a diffusion combustion mode. The concept has both high efficiency and low soot emission due to low heat losses and less stratified fuel and air mixtures compared to conventional diesel CI. The mechanisms behind the combustion process are not yet very well known. This work focuses on the efficiency and the in-cylinder process in terms of fuel distribution and the initial phase of the combustion. More specifically, double injection strategies are compared with single injection strategies to achieve different levels of stratification, ranging from HCCI to PPC like combustion as well as poor (43%) to good (49%) of gross indicated efficiency. The experiments were performed in an optical heavy-duty CI engine. To analyze how the efficiency was affected in a transition from HCCI to PPC, the natural luminosity (N.L.) was captured with high-speed video (HSV). To complement the HSV data, fuel, temperature, and oxygen distribution were explored by Computational fluid dynamics (CFD) simulation. The results show that the jet-jet and jet-piston interactions can be modified and can reshape the transition trends of gross indicated efficiency and ignition location compared to a single injection. In the transition region, these interactions can improve the efficiency by shaping the fuel-rich region away from cold areas, like the vertical wall of the piston and the squish region, to avoid fuel wetting and incomplete combustion. However, with double injections in the piston bowl (PPC region), jet-jet interaction can unfortunately inhibit the mixing process of the second fuel jet and oxygen due to interaction with the fuel rich region from the first injection, ending up with a lower combustion efficiency.
The main objective of this study is to evaluate the characteristics of combustion that combine premixed charge compression ignition (PCCI)-based combustion with conventional mixing controlled combustion. In this type of combustion, it is supposed that the combustion duration is shortened due to the synchronization of the timing of two types of combustions. In addition, the cooling loss caused by spray impingement is expected to decrease by the reduction of the proportion of mixing controlled combustion. In this study, the effect of injection pressure, injection timing, and split injection on thermal efficiency and emissions were investigated in order to determine the appropriate injection parameters for PCCI-based combustion to realize the proposed combustion concept.
To achieve simultaneous reduction of CO2 and NOx emission from the Dual-Fuel (DF) engine using natural gas and diesel fuel, Premixed Charge Compression Ignition (PCCI) type combustion is a promising technology. However, to apply this technology to the practical operation of the DF engine, combustion control is key challenge because the ignition of PCCI type combustion is governed by chemical reaction of natural gas/air and diesel fuel premixture and not controlled by direct control parameter such as spark timing of spark-ignition natural gas engine or diesel fuel injection timing of micro-pilot type DF engine. The focus of this study is to understand the effect of engine control parameters on DF-PCCI combustion characteristics to establish the combustion control strategy in medium speed DF engine. Engine experiments using a 4-stroke medium speed single cylinder engine were carried out. Firstly, early two stage diesel pilot injection was applied to realize DF-PCCI combustion. As a result, brake thermal efficiency was successfully improved by 2%pt compared with conventional micro-pilot combustion while achieving low NOx emission to meet the stringent emission standard. THC emission was successfully reduced at the same time. Secondly, the effects of engine control parameters on DF-PCCI combustion characteristics were investigated. Finally, DF-PCCI combustion control strategy in the medium speed engine is discussed and proposed based on the engine test results.
Physics-based models in a closed-loop feedback control of a premixed charge compression ignition (PCCI) engine can improve the combustion efficiency and potentially reduce harmful NOx and soot emissions. A stand-alone multi-zone combustion model has been proposed in the literature using a physics-based mixing approach. The scalar dissipation rate emerged as the determining parameter in the model for mixing among different zones in the mixture fraction space. However, the calculation of the scalar dissipation rate depends on three approaches: three-dimensional computational fluid dynamics (3-D CFD) combustion simulations based on representative interactive flamelet (RIF) model, tabulation, or an empirical algebraic model of the scalar dissipation rate fitted for the given operating conditions of the engine. While the 3-D CFD approach provides accurate results, it is computationally too expensive to use the multi-zone model in closed-loop control. Tabulation or empirical models are computationally cheap but are not physical, and hence, they limit the usability of the model to preset operating conditions. In this work, an integral model for the scalar dissipation rate based on the one-dimensional cross-sectionally averaged multi-phase spray equations is proposed as a first step towards model-based control. Due to the 1-D character of the resulting equations, time to solution is significantly reduced compared to full 3-D CFD models. The model provides distribution of fuel in the liquid and vapor phase as well as the scalar dissipation rate in physical space and time. The integral model coupled to a flamelet solver constitutes the integral combustion model, which can capture unsteady non-premixed combustion behavior. The model is able to reasonably predict ignition delay times for the Spray A case compared to 3-D CFD as well as measurements. The model can capture trends of the ignition delay time with respect to oxygen concentration as well as temperature. While the model is still not sufficiently fast for feedback control, as a physics-based stand-alone model based on the solution of partial differential equations, it will serve as a very good basis for further model reductions. The new method can also be used to generate data to train artificial neural networks that can then be used in model-based feedback control.
The objectives of this study are to investigate the effects of premixed charge compression ignition (PCCI) strategies with split injection on soot emission characteristics. The split injection conditions included three injection intervals (1.1 ms, 1.3 ms, and 1.5 ms) and three injection quantity fraction ratios (Q1/Q2 = 10.0/14.6 mm3/st, 15.2/9.4 mm3/st, and 20.0/4.6 mm3/st). The results in real engine tests showed that shorter injection intervals, and the 1st injection quantity contributes to reduced soot emissions. A rig test with high-pressure and high-temperature constant-volume vessel (CVV) and a two-dimensional (2D) model piston cavity were used to determine correlations between injection conditions and soot emissions. During the rig test, fuel was injected into the CVV by a single-hole nozzle under split injection strategies. The injection strategies include the same injection intervals and quantity fraction ratios as in the real engine test. The 2D piston cavity model took the same shape as that used in a small-bore diesel engine to investigate spray development, mixture formation, and combustion process. Tracer laser absorption scattering (LAS) was used to observe the spray development and mixture formation processes without combustion. The spatial distributions of the vapor and liquid phases and spray mixture formation characteristics in the 2D piston cavity were investigated. Spray combustion and soot formation processes were studied using a high-speed video camera. The flame structure and soot formation process were examined using two-color pyrometry. The experimental results revealed that the split injection interval and mass fraction ratio influence the characteristics of the mixture formation and soot formation processes in the 2D piston cavity. The rig test results show that the correlation between soot emission characteristics and injection strategies is similar to that observed in the rig test.
Premixed charge compression ignition (PCCI) is an advanced combustion mode that has the aim of simultaneously reducing particulate matter and nitrogen oxide exhaust emissions, compared with conventional diesel combustion, thanks to a partially premixed charge and low temperature combustion. In this work, PCCI combustion has been implemented by means of an early single-injection strategy and large amounts of recirculated exhaust gas. Starting from a commercial Euro VI on-road engine, the engine hardware has been modified to optimize PCCI operations. This has involved adopting a smaller turbo group, a new combustion chamber and injectors, and a dedicated high-pressure exhaust gas recirculation system. The results, in terms of engine performance and exhaust emissions, under steady-state operation conditions, are presented in this work, where the original Euro VI calibration of the conventional engine has been compared with the PCCI calibration of the optimized hardware engine. The obtained results show that the engine-out nitrogen oxides and soot were dramatically reduced, and this can offer the possibility of reviewing the after-treatment system. The penalties, in terms of brake specific fuel consumption, were generally below 10%, compared with the Euro VI configuration. The main limitations were derived from the combustion noise and the hydrocarbon and carbon monoxide emissions at the exhaust, which could represent an issue, especially when the exhaust temperature is not high enough to allow the diesel oxidation catalyst to work with high conversion efficiencies. Furthermore, the effect of EGR cooler fouling on the performance and emissions has been presented and discussed. The increased pressure drop across a fouled EGR cooler results in a reduced amount of exhaust gas recirculation, thus posing a serious problem for PCCI calibration activity.
In order to meet the requirements in the stringent emission regulations, more and more research work has been focused on homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) or partially premixed compression ignition (PCCI) as they have the potential to produce low NOx and soot emissions without adverse effects on engine efficiency. The mixture formation and charge stratification influence the combustion behavior and emissions for PPC/PCCI, significantly. An ultra-high speed burst-mode laser is used to capture the mixture formation process from the start of injection until several CADs after the start of combustion in a single cycle. To the authors’ best knowledge, this is the first time that such a high temporal resolution, i.e. 0.2 CAD, PLIF could be accomplished for imaging of the in-cylinder mixing process. The capability of resolving single cycles allows for the influence of cycle-to-cycle variations to be eliminated. This ability to study individual cycles aids the understanding of the mixture formation process as well as the cycle-to-cycle variations. Strong air entrainment at the boundary layer can be clearly observed and followed as the mixing process progresses. The formation of eddies created by the shear force and their rotational motion can be continuously observed during the mixing process. The interaction between two adjacent spray plumes in the recirculation zone is well captured and studied. In addition, the mixing process resulting in the stratified fuel charge being located in the recirculation zone before the SOC while the areas along the original spray axis are leaned out after the end of injection, can be followed in one time sequence. Moreover, the auto-ignition position and early flame development can be studied, from the high-speed chemiluminescence imaging, together with the fuel distribution in the combustion chamber.
With ever-demanding emission legislations in Compression Ignition (CI) engines, new premixed combustion strategies have been developed in recent years seeking both, emissions and performance improvements. Since it has been shown that in-cylinder air flow affects the combustion process, and hence the overall engine performance, the study of swirling structures and its interaction with fuel injection are of great interest. In this regard, possible Turbulent Kinetic Energy (TKE) distribution changes after fuel injection may be a key parameter for achieving performance improvements by reducing in-cylinder heat transfer. Consequently, this paper aims to gain an insight into spray-swirl interaction through the analysis of in-cylinder velocity fields measured by Particle Image Velocimetry (PIV) when PCCI conditions are proposed. Experiments are carried out in a single cylinder optical Diesel engine with bowl-in-piston geometry. A standard 2D PIV system is used for measuring instantaneous velocity fields in a cross section (swirl-plane) inside the combustion chamber. The test matrix is based on an advanced single pilot injection with energizing time and injection pressure sweeps at different crank-angles. Results show that swirl ratio decreases with the increase of injected fuel mass. The decrease in swirl ratio also comes with a homogenization of the flow field. This homogenization along with lower swirl ratios might decrease heat transfer to cylinder walls.
Impingement of spray against the cylinder wall or piston bowl is an unavoidable physical process in homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI) engines using early injection strategy. It directly affects fuel-air mixture formation, combustion and exhaust emission. In addition, the alcohol fuels such as methanol, ethanol and n-butanol are regarded as hopeful alternative fuels as well as fuel additive for HCCI and PCCI diesel engines to improve the emission level. The better understanding for the effect of alcohol-diesel blending fuel on the spray-wall impingement process is helpful for the improvement of HCCI and PCCI diesel engines. In this paper, the effects of three different alcohol-diesel blending fuels (methanol, ethanol and n-butanol) on the spray-wall impingement process were studied. Numerical investigation was performed in AVL FIRE code. The predicted equivalence ratio and droplet distribution in the spray-wall impingement region were discussed. The spray-wall impingement region was divided into three regions which were the main wall-jet region, the stagnation region, and the downstream region. The history of calculated droplet tangential velocity in each region was analyzed. Besides, overall Sauter mean diameter (SMD) and local SMD of the impinged spray at different heights were also compared. Conclusions drawn from the simulation results suggested that methanol-diesel blending fuel with high substitution ratio could obtain more homogenous near-wall mixture and smaller local/overall SMD. The ratio of spray-wall impingement of the methanol-diesel blending fuel was smaller than the other two alcohol-diesel blending fuels due to the lower boiling point, smaller droplet SMD and higher droplet reverse velocity. In addition, droplet tangential velocity distribution of the different alcohol-diesel blending fuels was influenced by the combined effect of density, viscosity and surface tension. For droplet overall and local SMD, the effect of the boiling point should be considered.
Primary Reference Fuels (PRFs) - binary mixtures of n-heptane and iso-octane based on Research Octane Number (RON) - are popular gasoline surrogates for modeling combustion in spark ignition engines. The use of these two component surrogates to represent real gasoline fuels for simulations of HCCI/PCCI engines needs further consideration, as the mode of combustion is very different in these engines (i.e. the combustion process is mainly controlled by the reactivity of the fuel). This study presents an experimental evaluation of PRF surrogates for four real gasoline fuels termed FACE (Fuels for Advanced Combustion Engines) A, C, I, and J in a motored CFR (Cooperative Fuels Research) engine. This approach enables the surrogate mixtures to be evaluated purely from a chemical kinetic perspective. The gasoline fuels considered in this study have very low sensitivities, S (RON-MON), and also exhibit two-stage ignition behavior. The first stage heat release, which is termed Low Temperature Heat Release (LTHR), controls the combustion phasing in this operating mode. As a result, the performance of the PRF surrogates was evaluated by its ability to mimic the low temperature chemical reactivity of the real gasoline fuels. This was achieved by comparing the LTHR from the engine pressure histories. The PRF surrogates were able to consistently reproduce the amount of LTHR, closely match the phasing of LTHR, and the compression ratio for the start of hot ignition of the real gasoline fuels. This suggests that the octane quality of a surrogate fuel is a good indicator of the fuel’s reactivity across low (LTC), negative temperature coefficient (NTC), and high temperature chemical (HTC) reactivity regimes.
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