Homogeneous Charge Compression Ignition Operation Research Articles

Effects of temperature and composition inhomogeneity on the ignition characteristics of NH3/H2 co-firing fuels under HCCI operating conditions

The application of ammonia (NH3) in combustion devices, such as internal combustion engines (ICEs), is expected to largely reduce the greenhouse gas (CO2) emission. NH3/H2 cofiring fuels in homogeneous charge compression ignition (HCCI) engines may provide a potential way to deal with zero carbon requirements. However, in HCCI engines, the ignition process needs to be moderated since the ignition is only controlled by the chemical kinetics of the fuel. Therefore, this study investigates the effects of temperature and composition stratification strategies on the auto-ignition characteristics of NH3/H2/air mixtures under HCCI engine operating conditions with direct numerical simulation (DNS). 12 cases with different stratification strategies have been set under turbulent conditions. The chemical kinetics of NH3/H2/air was verified with the laminar flame speeds and ignition delay times. Results show that the temperature stratification can reduce the peak value of heat release rate (HRR), advance the ignition time and extend the combustion duration. In this case, the chemical reaction front is dominated by the deflagration or flame propagation mode. However, in contrast, composition stratification shows very limited effect on the overall combustion process, which is similar to homogeneous ignition and denoted as the spontaneous ignition mode. When increasing the hydrogen content in the fuel, the ignition time is obviously advanced and the peak of HRR is slightly increased. Higher NO emission is also observed which is mainly due to the increase of O, H, and OH intermediates to enhance the fuel NO production. Temperature stratification degree can improve the ignition process under both negatively correlated or unrelated T-Φ fields. However, the improvement is more evident for unrelated T-Φ condition when increasing the stratification degree.

Experimental study on controlled hot surface assisted compression ignition (HSACI) in a naturally aspirated single cylinder gas engine

Homogeneous charge compression ignition (HCCI) promises low [Formula: see text] emissions and high efficiency due to fast combustion at low temperatures. However, the control of combustion timing represents a serious challenge due to the lack of dedicated ignition control parameters. This challenge is addressed in this work by means of a hot surface ignition (HSI) system, whose core element consists of a shielded, electrically heated ceramic glow plug. In this approach, termed as hot surface assisted compression ignition (HSACI), a small portion of mixture is thought to ignite in the vicinity of the shielded glow plug and to subsequently propagate to the main combustion chamber in order to initiate bulk-gas auto-ignition. Adjusting the hot surface temperature enables to either advance or retard the onset of combustion and thus, allows to control combustion timing. This paper presents experimental results of initial engine trials, using the HSACI concept in a naturally aspirated single cylinder natural gas engine. Measurements were conducted at a constant engine speed of 1400 l/min and include intake air temperatures in the range of 150–175°C and relative air-fuel ratios ([Formula: see text]) from 2.0 to 2.8. Results show that the HSI system enables combustion under conditions, which do not allow for pure HCCI operation. Moreover, the combustion timing can be actively controlled within certain limits by changing the HSI temperature. Increasing cycle-to-cycle variations limit stable operation at lower temperatures, while a transition to pure HCCI is found at intake temperatures beyond 170°C. The applicable [Formula: see text] range is limited by knocking or uncontrolled combustion toward the rich side and instable operation toward the lean side. Loss analysis points out that wall heat flow and imperfect combustion represent the dominant loss mechanisms. Heat release analysis reveals two pronounced phases, indicating initial flame propagation and subsequent auto-ignition similar to spark assisted compression ignition (SACI).

Combustion Characteristics of Biogas Fuel Using Particularly Simplified Reaction Mechanism for HCCI Engines

Renewable energy resources like biogas fuel are highly needed to overcome the increasing demands on energy and to allow more efficient power transformation. Biogas is not investigated adequately in homogenous charge compression ignition (HCCI) engines and no specific chemical kinetics were proposed for its combustion in HCCI engines. In this study, a reaction mechanism had been proposed to simulate biogas combustion in HCCI engines. A combined mechanism reduction algorithm, using a graph-based approach and sensitivity analysis, was used to reduce a full detailed mechanism for C1-C4 hydrocarbon fuels. The resulted mechanism consists of 42 species and 328 reactions that were selected to predict the ignition delay time of the HCCI ignition process. The new mechanism was implemented in a modified multizone combustion model using CANTERA flow reactions and MATLAB software. Many combustion parameters, including pressure and temperature profiles, ignition time, produced work, and heat release rate, were estimated. It was found that HCCI engines fueled with biogas can be an effective option for power generation applications at wide range of CH4-CO2 ratios. Furthermore, the reaction mechanism showed high ability in predicting the experimental data at HCCI operation conditions over a wide range of temperature (500–2,000 K) and equivalence ratios (0.4–1.8). This allows further investigations of the mechanism for combustion and emissions prediction at many different operation conditions.

Effects of operating parameters on the performance, emission and combustion indices of a biogas fuelled HCCI engine

This study discusses the operation of a Homogeneous Charge Compression Ignition (HCCI) engine using simulated biogas and diethyl ether (DEE) as the primary and secondary fuels respectively. Performance, emission and combustion parameters are measured for various biogas flow rates (8–16 litre/min), composition (50 to 100% methane), intake temperatures (35–80 °C) and loads (20 to 90% of full load). A comparison of injecting DEE at the intake port (port injection) and 7 cm upstream (manifold injection) is also presented. It was demonstrated that at high flow rates and/or with high methane content, biogas can effectively substitute DEE and provide up to 60% of the total energy input. However, the use of lower biogas flow rates and methane fraction resulted in better thermal efficiency (as high as 26%) as well as lower HC emissions. HCCI operation offered simultaneously low NOx (< 0.2 g/kWh) and smoke (~1%). Intake heating ensured better performance and emissions, although it increased the tendency to knock. In general, manifold injection provided superior engine output compared to port injection. The knock limit of HCCI operation could be effectively extended by employing high biogas flow rates and/or methane enrichment. ANOVA study showed that biogas flow rate had a strong influence on most engine output parameters. While methane fraction correlated well with combustion indices, engine torque had a significant effect on thermal efficiency and emissions.

Gasoline fuels properties for multi-mode operation – Observations in a GDI and the CFR engine

The combustion behavior of five full boiling range RON98 gasoline blends was evaluated for multi-mode operation in a GDI and the CFR octane rating engine. The GDI engine tests were conducted with stoichiometric air-fuel ratio in spark-ignition (SI), and with air-diluted homogeneous charge compression ignition (HCCI) mode. In the CFR engine, the knocking combustion was analyzed under standard RON testing conditions at both peak knocking lambda and stoichiometric air-fuel ratios, whereas compression ignited operation was characterized by utilizing the HCCI number test protocol. Disparate knock limited SI and HCCI combustion behavior was observed for the test fuels, despite four of the fuels having the same RON and octane sensitivity. It was found that knock-limited combustion phasing in the GDI engine did not align well with the RON. However, a detailed comparison of knock-limited SI operation in the GDI and CFR engine revealed that a more appropriate effective RON based on a common knock intensity metric (MAPO) and stoichiometric air-fuel ratio resulted in comparable knock characterization between the two engine platforms. Furthermore, the critical intake air temperature and the critical compression ratio were proposed to characterize knock-limited SI operation, while the minimum intake air heating and compression ratio were used to define a fuel’s autoignition propensity for compression ignition operation in the GDI and CFR engine, respectively. Finally, each fuel’s characteristic compression ratio needed to obtain knock-limited SI (KLSI) and HCCI operation was used to calculate an effective multi-mode octane number (MM-ON) based on the primary reference fuel blends.

Biodiesels powered in-cylinder common rail direct injection (CRDi) Assisted Homogeneous Charge Compression Ignition (HCCI) engine

ABSTRACT Experimental tests were performed on homogeneous charge compression ignition (HCCI) with in-cylinder direct injection (DI) of diesel, biodiesel of Ceiba Pentandra oil methyl ester (CPOME) and biodiesel of Acid oil methyl ester (ACOME). Initially some trial experiments were conducted at different fuel injection timing (IT) to distinguish the HCCI operation from common rail direct injection (CRDI) operation. For this, heat release rate (HRR) analysis, trial experiments were conducted for 40 % Load. The cool flame always started at about 20° before top dead centre (bTDC) showing HCCI operation started with fuel IT advancement of 50° bTDC and more. HCCI engine showed lowered peak HRR and retarded one. Higher injection pressure (IP) lowered oxides of nitrogen (NOx) due to lower HRR. NOx of 42 ppm, 36 ppm and 34 ppm were achieved with diesel, ACOME and CPOME respectively at IP 900 bar and IT of 80° bTDC in HCCI mode. Lower smoke of 9 HSU, 15 HSU and 17 HSU was achieved with diesel, ACOME and CPOME respectively at the same operating conditions. Overall, it could be concluded that, IP 900 bar and IT of 80° bTDC are the best operating conditions to reduce NOx and smoke with slightly lower brake thermal efficiency (BTE) in HCCI mode.

An experimental investigation on combustion and performance characteristics of supercharged HCCI operation in low compression ratio engine setting

This study investigates the effects of boost pressure on combustion and performance of an early direct injection homogenous charge compression ignition (HCCI) engine at a low compression ratio (CR). A 2.0 L, four-cylinder, four-stroke, gasoline direct injection engine was converted to operate in early direct injection HCCI mode. In addition, a supercharger unit was developed for engine boosting. The experiments were performed at different intake manifold absolute pressures (MAP) from 1.0 to 1.6 bar at different engine loads using n-heptane fuel. The effects of boost pressure were investigated on HCCI combustion and engine performance characteristics using volumetric efficiency, in-cylinder pressure, heat release rate (HRR), maximum in-cylinder pressure and gas temperature, CA50 (crank angle by which 50% of the fuel is burnt), combustion duration, apparent combustion efficiency, indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP), friction mean effective pressure (FMEP), indicated thermal efficiency (ITE), brake thermal efficiency (BTE), heat loss, exergy of heat loss, coefficient of variation of IMEP (COVIMEP), maximum pressure rise rate (MPRR) and ringing intensity (RI). The experimental results showed that high-efficiency HCCI operation is feasible at an engine compression ratio as low as 9.2 once the engine variables are properly optimized and an appropriate level of supercharging is utilized. An increase in indicated thermal efficiency was seen as boost pressure increased. In addition, combustion phasing advanced by increasing boost pressure or increasing air–fuel equivalence ratio values. Combustion events with CA50 2–3 °CA aTDC show the highest thermal efficiency especially at low boost pressure conditions. In addition, the pressure rise rate and ringing intensity increased by increasing air–fuel equivalence ratio and MAP. The test results also showed that HCCI operating range can be extended with the increase of intake manifold pressure especially at high load limits.

Computationally efficient evaluation of optimum homogeneous charge compression ignition operating range with accelerated multizone engine cycle simulation

The very intensive calculations necessary to define a performance map requiring evaluation of over a hundred individual operating points can be efficiently conducted with accelerated multizone for engine cycle simulation, leading to a definition of regions of acceptable and optimum homogeneous charge compression ignition operation. Accelerated multizone for engine cycle simulation has the virtue of enabling accurate evaluation of many operating conditions based on thermal stratification data from a single fluid mechanics run at motored conditions. This is possible because thermal stratification is more sensitive to engine geometry than to operating conditions. In this article, accuracy of accelerated multizone for engine cycle simulation is demonstrated by comparison with experimental data for iso-octane homogeneous charge compression ignition operation over a broad range of lean equivalence ratios (0.14–0.28). The validated accelerated multizone for engine cycle simulation model is then applied to generating a performance map for an engine controlled by appropriately adjusting equivalence ratio and internal exhaust gas recirculation. Regions of acceptable and optimum combustion are identified. It is finally demonstrated that while indicated mean effective pressure remains low for optimum homogeneous charge compression ignition operation (1–4 bar), this is sufficient for a large fraction of typical driving in light-duty vehicles. Much driving including idle can therefore be done in homogeneous charge compression ignition mode at high efficiency and low (essentially zero) NO x and particulate matter emissions.

Autoignition behavior of a full boiling-range gasoline: Observations in RCM and GCI engine environments

The understanding of, and capability to modulate fuel autoignition behavior are important aspects towards the development of advanced, low temperature combustion (LTC) engine concepts, which have potential to significantly increase engine efficiency while at the same time addressing emissions concerns. Proper combustion phasing and control of heat release rates via, for instance, multiple injections and exhaust gas recirculation, are significant challenges that can vary with fuel composition. Overall reactivity, which is a strong function of the in-cylinder temperature and pressure, is a prime driver for regulating combustion timing, while preliminary exothermicity, in the form of low- and intermediate-temperature heat release (LTHR, ITHR) can inhibit, or facilitate operational success, e.g., control combustion phasing. There are still gaps in understanding these features and how they interact with needs of advanced combustion engines, and how practical fuels can be rated for the new challenges of LTC engines.This work utilizes a rapid compression machine (RCM) and gasoline compression ignition (GCI) engine to probe the autoignition behavior of a California Reformulated Gasoline Blendstock for Oxygenate Blending (CARBOB) (RON = 86, MON = 81.4) under quasi- homogeneous charge compression ignition (qHCCI) operation. A wide range of thermodynamic conditions is explored (Tc = 700–1000 K, Pc = 15–90 bar) where ignition delay times and LTHR/ITHR are quantified. Both stoichiometric, dilute (11% O2) and lean (equivalence ratio (ϕ) = 0.23) fuel loading conditions are considered. The GCI engine is operated under fuel-lean conditions (ϕ = 0.23) using no external exhaust gas recirculation over a range of intake temperature (Tin = 30–70 °C), with the intake pressure adjusted (Pin = 1.2–1.3 bar) to achieve constant combustion phasing (CA50 = −4 °aTDC). Preliminary exothermicity is also quantified under these conditions.The stoichiometric, dilute RCM measurements reveal negative temperature coefficient (NTC) behavior for this fuel and indicate that rates and extents of LTHR and ITHR are both affected by the compressed conditions, with temperature imposing an inverse dependence, while increased pressure causes LTHR to increases, but ITHR to decrease. These are the first experimental quantifications of ITHR trends for a practical fuel under well-controlled, static conditions. When the lean RCM measurements are mapped to the in-cylinder conditions of the engine, it is found that under a constant combustion phasing scenario (as used in the engine), the fuel has little overall temperature sensitivity, while the starts of high temperature heat release (soHTHR) and top dead center (TDC) points seen along the engine compression trajectories correspond to isopleths of ignition delay times τRCM = 6 and 3 ms, respectively. In addition, the points of peak LTHR rate in the engine correspond to an isopleth of first-stage ignition τ1,RCM = 0.50–0.75 ms. Correlating the magnitudes of LTHR and ITHR measured in the RCM to the engine requires quantification of the preliminary exothermicity at the thermodynamic conditions of peat LTHR rate and soHTHR, respectively. The current measurements demonstrate how fundamental data from an RCM can be used to project expected trends in overall fuel reactivity to a qHCCI engine environment, and thus provide a possible avenue for characterizing fuels for LTC engines.

Effects of combustion timing on pressure rise rates in a residual effected HCCI engine

Realization of a low temperature combustion concept in homogeneous charge compression ignition (HCCI) engines is a cutting-edge technology that offers clean combustion in parallel with high thermal efficiency. Low combustion temperature prevents from NOx for-mation whereas homogeneous mixture assures smokeless exhaust. However, achieving the production feasibility by HCCI technology is hampered by high pressure rise rates and the resulting combustion noise at a high load operation. This paper explores combustion tim-ing parameters that are capable of maintaining permissible levels of pressure rise rates under a high load regime. On the basis of exper-imental data collected at a high load HCCI operation, pressure rise level was correlated with combustion duration. Furthermore, com-bustion duration has been found to scale with in-cylinder volume, for which 50% of mass fraction burned appeared. The results showed quantitatively limitations of engine load, pointing out on required combustion timings to achieve acceptable combustion harshness de-pending on engine load.

Three Way Catalyst-Selective Catalytic Reduction Aftertreatment System Evaluation for a Lean Burn Gasoline Engine Operating in Homogenous Charge Compression Ignition, Spark-Assisted Compression Ignition, and Spark-Ignited Combustion Modes

Low temperature and dilute homogenous charge compression ignition (HCCI) and spark-assisted compression ignition (SACI) can improve fuel efficiency and reduce engine-out NOx emissions, especially during lean operation. However, under lean operation, these combustion modes are unable to achieve Environmental Protection Agency (EPA) Tier 3 emissions standards without the use of lean aftertreatment. The three way catalyst (TWC)-SCR lean aftertreatment concept investigated in this work uses periodic-rich operation to produce NH3 over a TWC to be stored on a selective catalytic reduction (SCR) catalyst for NOx conversion during subsequent lean operation. Experiments were performed with a modified 2.0 L gasoline engine that was cycled between lean HCCI and rich SACI operation and between lean and rich spark-ignited (SI) combustion to evaluate NOx conversion and fuel efficiency benefits. Different lambda values during rich operation and different times held in rich operation were investigated. Results are compared to a baseline case in which the engine is always operated at stoichiometric conditions. SCR system calculations are also presented to allow for comparisons of system performance for different levels of stored NH3. With the configuration used in this study, lean/rich HCCI/SACI operation resulted in a maximum NOx conversion efficiency of only 10%, while lean/rich SI operation resulted in a maximum NOx conversion efficiency of 60%. If the low conversion efficiency of HCCI/SACI operation could be improved through higher brick temperatures or additional SCR bricks, calculations indicate that TWC-SCR aftertreatment has the potential to provide attractive fuel efficiency benefits and near-zero tailpipe NOx. Calculated potential fuel efficiency improvement relative to stoichiometric SI is 7–17% for lean/rich HCCI/SACI with zero tailpipe NOx and −1 to 5% for lean/rich SI with zero tailpipe NOx emissions. Although the previous work indicated that the use of HCCI/SACI increases the time for NH3 to start forming over the TWC during rich operation, reduces NH3 production over the TWC per fuel amount, and increases NH3 slip over the SCR catalyst, if NOx conversion efficiency could be enhanced, improvements in fuel efficiency could be realized while meeting stringent tailpipe NOx standards.

Evaluation of wall heat flux calculation methods for CFD simulations of an internal combustion engine under both motored and HCCI operation

In the present work, a study of different numerical heat transfer models is presented used for Homogeneous Charge Compression Ignition (HCCI) internal combustion engine simulations. Since the heat loss through the walls of an engine is an important parameter during engine optimization, as it influences power, efficiency and emissions, accurate modeling techniques need to be available. In this work, the predictive capability of different Computational Fluid Dynamics (CFD) models has been assessed, by using data obtained from experiments on a Cooperative Fuel Research (CFR) engine, a simple single cylinder pancake engine, which has been probed with local heat flux sensors into the combustion chamber walls. The open-source software OpenFOAM® was used to perform simulations of this engine, under both motored and HCCI operation, with a specific focus on the performance of different heat flux models. Due to the simple engine geometry, more numerically demanding heat flux modeling methods could be used, maintaining an acceptable computation time. This allowed a full comparison between the equilibrium wall models as in standard use, an improved empirical heat flux correlation and a numerically intensive low Reynolds formulation. The numerical results considering all aspects of the heat flux - both its progress in time as well as quantitative aspects such as the peak heat flux or the total heat loss - have then been compared to an extensive experimental database. This allowed a full analysis of the performance of the different methods. It was found that the low Reynolds formulation described the physical behavior near the wall the best, while predicting acceptable results concerning the heat flux through the engine walls. The best heat flux prediction was however obtained with an improved empirical model, which additionally has a much shorter computation time. This is crucial when moving on to heat flux simulations of more complex production-type engines. Lastly, the equilibrium models were never capable of accurately predicting the wall heat flux.

Effects of charge concentration and reactivity stratification on combustion and emission characteristics of a PFI-DI dual injection engine under low load condition

Both concentration stratification and reactivity stratification are beneficial for reducing the combustion rate and controlling the combustion phasing in HCCI (homogeneous charge compression ignition) operation. However, the different effects on combustion and emissions of concentration and reactivity stratification have not been fully explored and the interaction between the two stratification modes also needs to be clarified. Therefore, the effects of concentration stratification and reactivity stratification on combustion and emission characteristics were investigated in a single-cylinder diesel engine. The different concentration stratifications were designed by five port injection ratios to study the influence of concentration stratification. Cases with and without reactivity stratification were compared at the same overall reactivity and the same concentration stratification in the cylinder to roughly separate the impact of reactivity stratification. Results show that with the decrease of the premixed ratio, the peak heat release rate decreases, combustion phasing delays, and the thermal efficiency show the tendency of first decreasing and then increasing. For cases with same concentration stratification, the introduction of iso-octane/n-heptane reactivity stratification decreases combustion efficiency but increases indicated thermal efficiency, NOx (nitrogen oxides) emissions can be improved while CO (carbon monoxide) and HC (hydrocarbon) emissions are increased. The introduction of n-heptane/iso-octane reactivity stratification presents a positive effect on both thermal efficiency and combustion efficiency and contributes to the improvement in NOx, CO and HC emissions.

Evaluation of Homogeneous Charge Compression Ignition (HCCI) autoignition development through chemiluminescence imaging and Proper Orthogonal Decomposition

Homogeneous Charge Compression Ignition (HCCI) engines deliver high thermal efficiency and, therefore, low CO2 emissions, combined with low NOX and particulate emissions. However, HCCI operation is not possible at all conditions due to the inability to control the autoignition process and new understanding is required. A high-swirl low-compression-ratio, optically accessed engine that can produce overall fuel lean, axially stratified charge (richer fuel mixture close to the cylinder head was achieved using port injection against open valve and homogeneous mixture during injection against closed valve timing) was operated in HCCI mode without and with spark-assist mixture ignition. The present study investigates the differences in the HCCI autoignition process and the propagation of the autoignition front with homogeneous mixture or fuel charge stratification, internal Exhaust Gas Recirculation (iEGR) (introduced by utilizing different camshafts) and spark-assisted iEGR lean combustion. In order to visualize the HCCI process, chemiluminescence flame images, phase-locked to a specific crank angle, were acquired. In addition, time-resolved images of the developing autoignition flame front were captured. Proper Orthogonal Decomposition (POD) was applied to the acquired images to investigate the temporal and spatial repeatability of the autoignition front and compare these characteristics to the considered scenarios. The eigenvalues of the POD modes provided quantitative measure of the probability of the corresponding flame structures. The first POD mode showed higher probability of single autoignition sites originating from a particular location (depending on the scenario). However, the contribution from other modes cannot be neglected, which signified multiple locations of the single autoignition and also, multiple sites of self-ignition of the fuel-air mixture. It was found that increasing iEGR resulted in random combustion (multiple autoignition sites and fronts), which, however, became significantly non-random due to addition of spark-assisted ignition. It was identified in the POD analysis of the time-resolved flame images that the presence of inhomogeneity either in the temperature or the mixture fraction distribution increases the probability of random combustion during the very early stages of flame development. Thus, the fluctuations of heat release is higher during this period.

A Comparison of Three Ion Sensing Circuits in a Homogeneous Charge Compression Ignition Engine

ABSTRACTThe use of a spark plug ion sensor to detect combustion timing in a homogeneous charge compression ignition (HCCI) engine is a technique that could alleviate the need for pressure transducers, a more expensive alternative. One disadvantage of this approach is the difficulty in obtaining a strong signal at lower equivalence ratios. This article addresses and compares three ion sensing circuitries, namely a voltage follower, a notch filter circuit that removes the 60-Hz wall noise, and a notch filter whose output is coupled to a custom-built “integrator” circuit. The circuit optimizations are aimed at improving signal strength and reliability. The ion signal present in the combustion chamber is experimentally investigated in a 1.9-L Volkswagen engine, modified for HCCI operation and fueled with gasoline. Experiments are conducted across different intake temperatures, pressures, and equivalence ratios. It was found that the custom-built circuit provided the best ion signal strength and reliability.

Real-time modeling of ringing in HCCI engines using artificial neural networks

Intense ringing operation is one of the major drawbacks associated with homogeneous charge compression ignition (HCCI) engines at high load conditions that limits HCCI operation range and can damage engine parts. This study uses HCCI experimental data to investigate combustion noise and ringing operation in a 0.3 L converted-diesel HCCI engine. A novel method is utilized to operate the HCCI engine in the ringing region by periodic variation in injected fuel amounts. Combustion noise level (CNL) is investigated along with main HCCI combustion parameters and emissions. A strong correlation is found between the CNL and variation of in-cylinder pressure at 10, 15, 20 CAD aTDC (P10, P15 and P20) and maximum in-cylinder pressure (Pmax). These experimental findings are then used to design an artificial neural network (ANN) model to predict CNL for identifying normal and ringing regions. A large amount of experimental data at cyclic and steady-state operating conditions are used to evaluate the ANN noise level (ANL) model. The results indicate that the real-time ANL model can predict CNL with less than 0.5% error for the HCCI engine. The ANL model is of utility to identify engine operating limits to avoid the ringing operation.

An alternative approach to accommodate detailed ignition chemistry in combustion simulation

In the current work, we utilize a recently developed staged Livengood–Wu (L–W) correlation to evaluate and predict the two-stage ignition behaviors of different primary reference fuels (PRFs) under homogeneous reciprocating engine conditions, to demonstrate its capability in capturing detailed ignition kinetics in combustion simulation. Based on the understandings of the global and detailed kinetics of low-temperature chemistry, simplified Arrhenius-based global expressions were developed for both ignition stages, and a linear correlation was applied for the cool flame temperature rise at the end of the first stage, for PRFs with various octane number (ON) 0, 20, 60 and 87 under constant volume conditions. For their performance under homogeneous charge compression ignition (HCCI) conditions, it is shown that for the same engine speed, the inlet temperature range allowing for two-stage ignition shrinks with increased ON numbers, and eventually two-stage ignition turns into single-stage ignition with sufficiently high ON numbers. Based on the ignition database, the combustion phasing for all PRFs under a wide HCCI operation range are predicted with the staged L–W integral method with satisfactory accuracy, including the first- and second-stage ignition timing as well as the cool flame temperature rise. The sensitivities of each of the engine operation parameters are successfully captured, further demonstrating the applicability of the staged L–W method for realistic fuels with low temperature chemistry and its potential applications for engine combustion control. This study also provides an alternative approach of accommodating low temperature ignition kinetics in combustion simulation, especially useful for those under variable thermodynamic conditions.

A thermodynamic model for homogeneous charge compression ignition combustion with recompression valve events and direct injection: Part I — Adiabatic core ignition model

This two-part article presents a model for boosted and moderately stratified homogeneous charge compression ignition combustion for use in thermodynamic engine cycle simulations. The model consists of two components: one an ignition model for the prediction of auto-ignition onset and the other an empirical combustion rate model. This article focuses on the development and validation of the homogeneous charge compression ignition model for use under a broad range of operating conditions. Using computational fluid dynamics simulations of the negative valve overlap valve events typical of homogeneous charge compression ignition operation, it is shown that there is no noticeable reaction progress from low-temperature heat release, and that ignition is within the high-temperature regime ( T &gt; 1000 K), starting within the highest temperature cells of the computational fluid dynamics domain. Additional parametric sweeps from the computational fluid dynamics simulations, including sweeps of speed, load, intake manifold pressures and temperature, dilution level and valve and direct injection timings, showed that the assumption of a homogeneous charge (equivalence ratio and residuals) is appropriate for ignition modelling under the conditions studied, considering the strong sensitivity of ignition timing to temperature and its weak compositional dependence. Use of the adiabatic core temperature predicted from the adiabatic core model resulted in temperatures within ±1% of the peak temperatures of the computational fluid dynamics domain near the time of ignition. Thus, the adiabatic core temperature can be used within an auto-ignition integral as a simple and effective method for estimating the onset of homogeneous charge compression ignition auto-ignition. The ignition model is then validated with an experimental 92.6 anti-knock index gasoline-fuelled homogeneous charge compression ignition dataset consisting of 290 data points covering a wide range of operating conditions. The tuned ignition model predictions of [Formula: see text] have a root mean square error of 1.7° crank angle and R2 = 0.63 compared to the experiments.

Experimental investigation of the effect of engine settings on the wall heat flux during HCCI combustion

Homogeneous charge compression ignition (HCCI) engines are a promising alternative to traditional spark- and compression-ignition engines, due to their potential to achieve a high thermal efficiency and near-zero emissions of NOx and soot. In this work, the heat transfer from the bulk gas to the cylinder wall is measured during motored and HCCI operation in a single cylinder (CFR) engine fueled with n-heptane. Heat flux measurements in the cylinder wall and head show small spatial variation of the heat flux in the combustion chamber. Design of Experiments methods are applied to study the effect of the engine settings on the heat transfer. It is found that the inlet air temperature does not affect the heat flux under motored operation. Under fired operation, all engine settings affect the heat transfer, but none of their interactions are significant. The compression ratio and inlet air temperature have a quadratic effect on the peak heat flux and peak convection coefficient, whereas the mass fuel rate has a linear effect. For the total heat released, the compression ratio and inlet air temperature have a linear effect and the mass fuel rate has a quadratic effect on it. All engine settings affect the instantaneous heat flux.

Experimental investigation on the effect of charge temperature on ethanol fueled HCCI combustion engine

In this investigation, an attempt has been made to study by varying the charge temperature on the ethanol fueled Homogeneous charge compression ignition (HCCI) combustion engine. Ethanol was injected into the intake manifold by using port fuel injection technique while the intake air was heated for achieving stable HCCI operation. The effect of intake air temperature on the combustion, performance, and emissions of the ethanol HCCI operation was compared with the standard diesel operation and presented. The results indicate that the intake air temperature has a significant impact on in-cylinder pressure, ringing intensity, combustion efficiency, thermal efficiency and emissions. At 170°C, the maximum value of combustion efficiency and brake thermal efficiency of ethanol are found to be 98.2% and 43%, respectively. The NO emission is found to be below 11 ppm while the smoke emission is negligible. However, the UHC and CO emissions are higher for the HCCI operation.