Development of Fast Idle Catalyst Light-Off Strategy for Gasoline Compression Ignition Engine - Part 1

In the internal combustion engine types, the gasoline compression ignition engine (GCI engine) presents the potential and effective method to improve engine thermal efficiency and lower pollution emissions when compared to the spark-ignition engine (SI) and the compression ignition engine (CI engine), respectively. To improve those advantages of the GCI engine, new engine technologies are being developed to help the engine efficiently work with higher compression ratios or lower octane gasoline fuel at part load conditions. However, high smoke, soot, HC and CO formations, the part-load stability of the combustion phase, or autoignition at high load conditions are still challenging with the GCI engine. This chapter will introduce some technologies that help solve the GCI engine's challenges, these technologies are such as: injection strategy, exhaust residual gas strategy, biodiesel addition, and oxygen content. After the aforementioned technological implementations, a detailed investigation will be carried out to lay the scope on the GCI engine performance and its emission characteristics. Multiple injections may help improve combustion stability and engine efficiency when compared to a single injection strategy. The HC and CO emissions can be decreased when the engine applies a multiple injection strategy and GB05 as fuel. The increase in EGR helps to reduce autoignition for both single and numerous ignition strategies. The oxygen concentration has a sensitive effect on the delay of the ignition process. The reduced amount of oxygen concentration induces an increase in the ignition delay, which helps to reduce the auto-ignition.KeywordsGCI engineInjection strategyEGRGB blendsOxygen concentrate

By combining a clean fuel such as gasoline with a high efficiency thermodynamic cycle (compression ignition), it is possible to demonstrate a powertrain that is clean and efficient, thus breaking the historical trade-off between decreasing CO2 and reducing criteria pollutants. The gasoline compression ignition (GCI) engine is a promising technology that can be used to improve thermal efficiency while reducing emissions. Its low temperature combustion does however lead to several problems that need to be overcome. The present study relates to a method and system for combining the advantages of GCI engine technology into a hybrid electric vehicle (HEV) to maximize the benefits. A plausible path is to operate the GCI engine at conditions where the benefits of a GCI engine could be maximized and where an electric motor can supplement the conditions where the GCI is less beneficial. In this study, GCI engines with different cetane number (CN) fuels were selected, and a hybrid simulation tool was used to address the potential of the GCI engines into hybrid electric vehicles. Co-developments can demonstrate efficiency and emission solutions through the achievements of the study, which will address examples of the competitive powertrain and will introduce more than 30% of CO2 reduction vehicle by 2030.

<div class="section abstract"><div class="htmlview paragraph">Gasoline compression ignition (GCI) engines have been considered an attractive alternative to traditional spark ignition engines. Low octane gasoline fuel has been identified as a viable option for the GCI engine applications due to its longer ignition delay characteristics compared to diesel and in the volatility range of gasoline fuels. In this study, we have investigated the effect of different injection timings at part-load conditions using light naphtha stream in single cylinder engine experiments in the GCI combustion mode with injection pressure of 130 bar. A toluene primary reference fuel (TPRF) was used as a surrogate for the light naphtha in the engine simulations performed here. A physical surrogate based on the evaporation characteristics of the light naphtha has been developed and its properties have been implemented in the engine simulations. Full cycle GCI computational fluid dynamics (CFD) engine simulations have been successfully performed while changing the start of injection (SOI) timing from -50° to -11 ° CAD aTDC. The effect of SOI on mixing and combustion phasing was investigated using detailed equivalence ratio-temperature maps and ignition delay times. Both experimental and computational results consistently showed that an SOI of -30° CAD aTDC has the most advanced combustion phasing (CA50), with the highest NOx emission. The effects of the SOI on the fuel containment in the bowl of the piston, the ignition delay time, combustion rate and emissions have been carefully examined through the CFD calculations. It was found that the competition between the equivalence ratio and temperature is the controlling parameter in determining the combustion phasings.</div></div>

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

Engine performance and emissions of a six-stroke Gasoline Compression Ignition (GCI) engine with wide range of Continuously Variable Valve Duration (CVVD) control were numerically investigated at low engine load conditions. For the simulations, an in-house 3-D CFD code with high fidelity physical sub-models was used and the combustion and emissions kinetics were computed using a reduced kinetics mechanism for a 14-component gasoline surrogate fuel. Double injections were employed to effectively form the local fuel/air mixtures with optimal reactivity. Several valve timing and duration variations through the CVVD control were considered under both positive valve overlap (PVO) and negative valve overlap (NVO) conditions. Effects of intake-valve re-breathing between the first expansion and the second compression strokes were also investigated. Close attention was paid to understand the effects of two additional strokes of the engine cycle on the thermal and chemical conditions of charge mixtures that alter ignition, combustion and energy recovery processes. Double injections were found to be necessary to effectively utilize the additional two strokes for the combustion of overly mixed lean charge mixtures during the second power stroke (PS2). It was found that combustion phasing in both power strokes is effectively controlled by the intake valve closure (IVC) timing since it affects the effective compression ratio. Engine operation under NVO condition with fixed exhaust valve opening (EVO) and IVC timings tends to advance the ignition timing of the first power stroke (PS1) but has minimal effect on the ignition timing of PS2. Re-breathing was found to be an effective way to control the ignition timing in PS2 at a slight expense of the combustion efficiency. The operation of a six-stroke GCI engine could be successfully simulated and the operability range of the engine could be substantially extended by employing the CVVD technique. In addition, the control of valve timings could successfully control the thermodynamic and compositional conditions of in-cylinder mixtures that enable to control the combustion phasing.

Experimental study of combustion and emission characteristics of gasoline compression ignition (GCI) engines fueled by gasoline-hydrogenated catalytic biodiesel blends

We present an analysis of the ignition process in thermochemical conditions relevant to gasoline compression-ignition (GCI) engines using direct numerical simulation (DNS). Two-dimensional DNS modelling the interaction of turbulence with an igniting double mixing layer are carried out. Three different primary reference fuel (PRF) blends, PRF0, PRF70, and PRF90, to span a range of different possible compression ignition scenarios are investigated. The fuel chemistry is shown to significantly affect the ignition process and the transition to a fully burning high-temperature flame. All three cases exhibit a diffusively supported cool flame which propagates towards richer mixtures faster than expected from homogeneous ignition delays. High-temperature combustion (HTC) initiates in rich mixtures in the PRF0 case, in both rich and lean mixtures in the PRF70 case, and in lean mixtures in the PRF90 case, which is consistent with expectations from homogeneous ignition delays. Budget analysis shows that HTC flames are diffusively supported in all cases, and as a result progress more rapidly from the ignition location to surrounding mixtures than homogeneous ignitions suggest. A quantitative model is proposed for the premixed flame propagation speed in the stratified and autoignitive mixtures. By considering the effects of normalised residence time of reactant at the flame surface, the conditional mean turbulent flame speed, conditioned upon mixture fraction, can be related to 1D referenced laminar flame speeds. The mechanism of consumption of the stoichiometric surface is examined by considering both displacement speed statistics and by tracking each single edge flame front. In the PRF0 case the results show the stoichiometric surface is consumed mostly by propagating HTC fronts that are almost parallel to it, which is referred to parallel consumption mode, while results in the PRF70 and PRF90 cases show signatures of edge-flame propagation as a secondary mechanism. For edge-flame mode the contribution of tangential-to <i>Z </i>diffusion to the displacement speed prevails over that of normal-to-<i>Z</i> diffusion. Overall the results demonstrate significant fuel-chemistry effects on the evolution of the ignitions, which will probably translate into significant differences in flame structure in a practical GCI engine. <br> <b>Novelty and significance statement </b><br> This work presents the first DNS of turbulent, nonpremixed autoignition targeting fuel chemistry effects in gasoline compression ignition (GCI) engines. The novelty further arises from two aspects. First, it is the first study to quantitatively model flame displacement speed in autoignitive, stratified mixing layers using the residence time concept. Second, the evolution of edge flame fronts is tracked in complex turbulent flows to enable temporal characterisation of edge flame dynamics and reveal how tangential-to-mixture-fraction diffusion varies across different propagation modes. The significance lies in the implications for practical GCI engine design, as fuel chemistry significantly affects the flame structure, akin to how unravelling the diesel flame structure advanced engine design. These findings also highlight the need to improve practical CFD models, such as incorporating residence time into level-set-based approaches for accurate flame speeds, or characterising conditional fluctuations arising from mixed edge flame modes in flamelet or CMC models.

This article describes the results of a response surface model (RSM)-based numerical optimization campaign for spray-guided spark assistance at cold operations in a heavy-duty gasoline compression ignition (GCI) engine. On the basis of an earlier work on spark-assisted GCI cold combustion, a space-filling design of experiments (DoE) method was first undertaken to investigate a multitude of hardware design variables and engine operating parameters. The main design variables included the number of injector nozzles, fuel split quantities and injection timings, and spark timing. The objective variables were engine combustion efficiency (ŋc), maximum pressure rise rate (MPRR), and engine-out nitrogen oxide (NOx) emissions. A total of 150 design candidates were automatically generated using the Sobol sequence method provided by the commercial software package, CAESES. Then, closed-cycle computational fluid dynamic (CFD) spark-assisted GCI simulations under cold idling operations were performed. The outcomes from the CFD-DoE design campaign were utilized to construct high-fidelity RSMs that allowed for further design optimization of the spark plug- and fuel injector-related design variables, along with fuel injection strategy parameters. A merit function with respect to objective variables was formulated with an appropriate weight assignment on each objective variable. Finally, the best design candidate was identified from the RSM-based optimization process and further validated in the CFD analysis. The best design candidate showed the potential to significantly improve combustion efficiency (ŋc &gt; 90%) over the baseline at cold idle while satisfying MPRR and NOx emissions constraints (MPRR &lt; 5 bar/CAD and NOx &lt; 4.5 g/kWh).

Advanced combustion strategies have been proposed to improve fuel efficiency while minimizing exhaust emissions. Gasoline compression ignition (GCI) combustion featuring partially premixed compression ignition (PPCI) and diffusion combustion has been recognized as an attractive, viable combustion strategy for its potential and advantages over conventional diesel and gasoline engines. The optimization of the GCI engine system requires the development of a quasi-dimensional GCI combustion model capable of simulating GCI combustion while requesting less computational burden than CFD simulation, which is very critical in engine system simulation. This study developed a quasi-dimension, phenomenological combustion model for PPCI and diffusion combustion to facilitate the early development of GCI combustion strategy. Due to the limited GCI engine test results, additional parametric CFD studies were conducted and served as a reference to develop the GCI combustion model and investigate the effect on GCI combustion of thermal conditions typically considered during early strategy development. A reduced toluene primary reference fuel and ethanol (TPRFE) mechanism with 65 species and 283 reactions was used to simulate GCI combustion in CFD and quasi-dimension models. Additionally, the behavior of high-pressure gasoline spray was investigated using CFD to support the development of the phenomenological spray dynamics model. The traditional phenomenological SI and CI combustion model frameworks were improved to simulate gasoline PPCI-diffusion combustion accurately with the spray dynamics, air entrainment, ignition delay, and heat release sub-models. The traditional spray model was improved and validated using CFD simulation results as a reference. The CFD result identified a high level of fuel concentration at the spray tip due to the drag and pushing momentum by the following fuel packets. This observation was accounted for in the development of the spray model. The ignition delay was calculated by solving the chemistry kinetics and curve fitting using the identical chemistry mechanism employed in CFD analysis. This research demonstrated that the phenomenological combustion model developed in this study could simulate fuel spray, fuel atomization, ignition delay, and heat release process. The GCI model has been integrated into GT-Suite and successfully applied to improve the combustion process with the valvetrain system. Various variable valve actuation (VVA) strategies were investigated at low-load operating conditions, including early exhaust valve open (EEVO), late exhaust valve open (LEVO), negative valve overlap (NVO), positive valve overlap (PVO), and exhaust gas rebreathing (RB). The RB strategies were identified as the most effective in promoting in-cylinder gas temperature by increasing the hot internal residual

The stringent emission regulations and energy shortage put forward strict requirements for highly efficient and clean combustion for internal combustion engines. The gasoline compression ignition (GCI), which is a new advanced combustion concept, can obtain high efficiency and low emissions simultaneously without many modifications of standard diesel engines. However, little research has been carried out to synergistically optimize the operation parameters in a wide load range, especially fueled with the carbon neutrally biofuels. Therefore, in this paper, the effects of various operating parameters on engine performance, combustion, and emission characteristics of the gasoline compression ignition (GCI) strategy fueled with a blend of butanol and biodiesel were investigated. Specifically, the impact of butanol energy ratio, fuel direct injection timing, and exhaust gas recirculation (EGR) at the indicated mean effective pressure (IMEP) of 4, 8, and 14 bar and the butanol energy ratio of 60%, 70%, and 80% were examined. Result shown that the increase in butanol energy ratio decreased the fuel reactivity and worsen the combustion process, while the lower butanol energy was also disadvantage to the engine performance. The indicated thermal efficiency could achieve 48.5% when the butanol energy ratio was 70% at medium engine load. The earlier fuel injection timing was needed at low engine load, the EGR was necessary to inhibit the in-cylinder pressure rise at high engine load, in which the EGR rates of 20% at the IMEP of 8 bar and 30% at the IMEP of 14 bar could achieve the optimum engine performance, respectively. Meanwhile, the nitrogen oxides emissions shown a greatly decrease with the EGR rates increase, and it was less than 200 ppm at the IMEP of 14 bar when the EGR rates were 50%.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Increasing regulatory demand to reduce CO&lt;sub&gt;2&lt;/sub&gt; emissions has led to an industry focus on electrified vehicles while limiting the development of conventional internal combustion engine (ICE) and hybrid powertrains. Hybrid electric vehicle (HEV) powertrains rely on conventional SI mode IC engines that are optimized for a narrow operating range. Advanced combustion strategies such as Gasoline Compression Ignition (GCI) have been demonstrated by several others including the authors to improve brake thermal efficiency compared to both gasoline SI and Diesel CI modes. Soot and NO&lt;sub&gt;x&lt;/sub&gt; emissions are also reduced significantly by using gasoline instead of diesel in GCI engines due to differences in composition, fuel properties, and reactivity. In this work, an HEV system was proposed utilizing a multi-mode GCI based ICE combined with a HEV components (e-motor, battery, and invertor).&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;To determine the total fuel consumption over the FTP75 drive cycle, a fueling map from a multi-mode GCI combustion presented in a previous study was used as the input data set for the 1D HEV drive cycle model (GT Drive) of a mid-sized SUV. An HEV operation strategy was proposed and followed by parametric studies of components including the e-motor sizing (20 kW to 80kW) and the battery capacity (2Ah to 8Ah), and evaluation on their impacts on fuel consumption.&lt;/div&gt;&lt;/div&gt;

Effects of intake conditions and octane sensitivity on GCI combustion at early injection timings

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Ammonia is a carbon-free fuel alternative for the internal combustion engine decarbonization. However, its toxicity and less advantageous combustion characteristics including higher nitrogen-based engine-out emissions have delayed its use in power generation applications. Therefore, the use of a secondary and also carbon-free fuel such as hydrogen was proposed in the literature as a solution to promote and improve ammonia combustion while minimizing any modifications in engine parameters and control strategy that may be required when compared to using conventional hydrocarbon-based fuels. In addition, the higher resistance to autoignition of ammonia can allow operation at higher compression ratios in spark ignition applications, therefore increasing the thermal efficiency. The study presented here used a single-cylinder heavy-duty research engine converted to spark ignition operation to investigate medium load engine operation with ammonia-hydrogen blends in which hydrogen represented 30% to 60% of the total energy in the fuel blend, at an engine speed of 1000 rpm and an equivalence ratio of 0.8. To find the maximum brake torque (MBT) for each fuel blend, spark timing varied from -35 CAD to -5 CAD ATDC. Then, the effect of energy substitution ratio (defined as the ratio of the hydrogen energy to the total fuel blend energy) on engine performance (i.e., in-cylinder pressure data, apparent heat release rate, and indicated mean effective pressure) was analyzed. Results indicated that retarding the spark timing by 5 CAD was required to achieve the optimum IMEP every time ESR increased by 0.1. Then, hydrogen addition decreased the ignition delay and combustion duration by 37% and 20%, respectively, as ESR increased from 0.3 to 0.6. However, higher hydrogen fractions inside affected the combustion phasing in a negative way, therefore affecting the engine performance at the operating conditions investigated in this work.&lt;/div&gt;&lt;/div&gt;

Characteristics of a non-reacting spray from an outwardly opening hollow-cone injector with high-reactivity gasolines

&lt;div class="htmlview paragraph"&gt;The temperature and pressure of the charge, reached at the end of the compression stroke when an engine is cranked for starting, decide whether it will start and attain selfsustained running. These, in turn, are affected by the crevice volume in, and the blowby from, the engine, particularly at cold ambient temperatures and low cranking speeds. This paper presents a model to estimate these effects. Tentative values are proposed for the parameters that appear in the model based on experiments performed on small engines motored in a cold chamber. The model can be incorporated in engine cycle simulation programs to allow for crevice and blowby effects.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;It is impossible to prevent gas leakage entirely from an operating reciprocating engine. Gas may leak at the valves, the cylinder head gasket, the spark plug gasket, the injector gasket and the piston rings. The gas that leaks from the cylinder past the piston rings into the crankcase is termed “blowby”. Blowby constitutes the major part of the total gas loss from the cylinder [&lt;span class="xref"&gt;1&lt;/span&gt;] and, unlike the other leakages, cannot be eliminated completely. Gas leakage from an operating engine leads to a decrease in its performance and an increase in hydrocarbon emissions. In an engine that is cranked for starting, gas leakage reduces the temperature and pressure attained at the end of the compression stroke. Gas leakage is particularly severe at low cranking speeds and, in conjunction with the generally poor fuel distribution and preparation prevailing under these conditions, can inhibit cold starting at low ambient temperatures.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;There is another feature inherent in the design of the reciprocating engine which has a similar effect on cold starting in that it also reduces the temperature and pressure attained at the end of the compression stroke. This is the unavoidable presence of small crevices in communication with the working space of the cylinder. The working clearances of the engine such as the piston top land clearance, the clearance between the rings and their grooves and ring gaps constitute these crevices. Such crevices could also exist around the inner periphery of the head gasket, spark plug thread clearances, clearance between the fuel injector and its hole, etc. When the cylinder pressure rises, gas is compressed into these crevices where, because of the very large surface/volume ratio, it is cooled rapidly to the metal surface temperature. Thus, in effect, the crevices augment the heat losses from the charge and hamper cold starting. Though much of the crevice gas is returned to the cylinder when the pressure falls, some of it in the ring pack leaks into the crankcase as blowby.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;In spite of their importance, the analysis of the effects of gas leakage and crevices on engine performance has not received much attention so far. There have been a few attempts made to analyze blowby in engines [&lt;span class="xref"&gt;2&lt;/span&gt;,&lt;span class="xref"&gt;3&lt;/span&gt;]. The performance of the ring pack is influenced by (a) the movements and deflections of the rings under me action of gas pressure, inertia and friction forces, (b) the hydrodynamics of the oil film on the liner, and (c) the finish of the various surfaces moving relative to one another. In view of these complications, it is unlikely that a single comprehensive model that can predict the performance of ring packs of all engines at all operating conditions can be developed. This paper presents a simple model to estimate gas leakage and crevice effects on the engine cycle. Since cold starting at low ambient temperatures is of concern, the model is described as it applies to a motored engine; its extension to an operating engine is straightforward.&lt;/div&gt;