Search Results

The increasing use of downsized turbocharged gasoline engines for passengers cars and the new European homologation cycles (WLTC and RDE) both impose an optimization of the whole engine map. More weight is given to mid and high loads, thus enhancing knock and overfueling limitations. At low and moderate engine speeds, knock mitigation is one of the main issues, generally addressed by retarding spark advance thereby penalizing the combustion efficiency. At high engine speeds, knock still occurs but is less problematic. However, in order to comply with thermo-mechanical properties of the turbine, excess fuel is injected to limit the exhaust gas temperature while maximizing engine power, even with cooled exhaust manifolds. This also implies a decrease of the combustion efficiency and an increase in pollutant emissions. Water injection is one way to overcome both limitations.

Pre-chamber combustion (PCC) has re-emerged in recent last years as a potential solution to help to decarbonize the transport sector with its improved engine efficiency as well as providing lower emissions. Research into the combustion process inside the pre-chamber is still a challenge due to the high pressure and temperatures, the geometrical restrictions, and the short combustion durations. Some fundamental studies in constant volume combustion chambers (CVCC) at low and medium working pressures have shown the complexity of the process and the influence of high pressures on the turbulence levels. In this study, the pre-chamber combustion process was investigated by combustion visualization in an optically-accessible pre-chamber under engine relevant conditions and linked with the jet emergence inside the main chamber. The pre-chamber geometry has a narrow-throat. The total nozzle area is distributed in two six-hole rows of nozzle holes.

Demand for transport energy is growing but this growth is skewed heavily toward commercial transport, such as, heavy road, aviation, marine and rail which uses heavier fuels like diesel and kerosene. This is likely to lead to an abundance and easy availability of lighter fractions like naphtha, which is the product of the initial distillation of crude oil. Naphtha will also require lower energy to produce and hence will have a lower CO₂ impact compared to diesel or gasoline. It would be desirable to develop engine combustion systems that could run on naphtha. Many recent studies have shown that running compression ignition engines on very low Cetane fuels, which are very similar to naphtha in their auto-ignition behavior, offers the prospect of developing very efficient, clean, simple and cheap engine combustion systems. Significant development work would be required before such systems could power practical vehicles.

The efficiency of spark ignition (SI) engines is usually limited by the occurrence of knock, which is linked to fuel octane number. If running the engine at its optimal efficiency requires a high octane number at high load, a lower octane number can be used at low load. Saudi Aramco, along with its long-term partner IFP Energies nouvelles, has been developing a synergistic fuel engine system where the engine is fed by fuel with an octane number adjusted in real time, on an as needed basis, while running at its optimal efficiency. Two major steps are identified to develop this “Octane on Demand” (OOD) concept: First, characterize the octane requirement needed to run the engine at its optimal efficiency over the entire map. Then, select the best dual fuel combination, including a base fuel and an octane booster to fit this concept.

In the engine community, gasoline compression ignition (GCI) engines are at the forefront of research and efforts are being taken to commercialize an optimized GCI engine in the near future. GCI engines are operated typically at Partially Premixed Combustion (PPC) mode as it offers better control of combustion with improved combustion stability. While the transition in combustion homogeneity from convectional Compression Ignition (CI) to Homogenized Charge Compression Ignition (HCCI) combustion via PPC has been comprehensively investigated, the physical and chemical effects of fuel on GCI are rarely reported at different combustion modes. Therefore, in this study, the effect of physical and chemical properties of fuels on GCI is investigated. In-order to investigate the reported problem, low octane gasoline fuels with same RON = 70 but different physical properties and sensitivity (S) are chosen.

In this study, the impact of the intake valve timing on knock propensity is investigated on a dual-fuel engine which leverages a low octane fuel and a high octane fuel to adjust the fuel mixture’s research octane rating (RON) based on operating point. Variations in the intake valve timing have a direct impact on residual gas concentrations due to valve overlap, and also affect the compression pressure and temperature by altering the effective compression ratio (eCR). In this study, it is shown that the fuel RON requirement for a non-knocking condition at a fixed operating point can vary significantly solely due to variations of the intake valve timing. At 2000 rpm and 6 bar IMEP, the fuel RON requirement ranges from 80 to 90 as a function of the intake valve timing, and the valve timing can change the RON requirement from 98 to 104 at 2000 rpm and 14 bar IMEP.

The objective of this paper is to present the results of the GT Power calibration with engine test results of the air loop system technology down selection described in the SAE Paper No. 2012-01-0831. Two specific boosting systems were identified as the preferred path forward: (1) Super-turbo with two speed Roots type supercharger, (2) Super-turbo with centrifugal mechanical compressor and CVT transmission both downstream a Fixed Geometry Turbine. The initial performance validation of the boosting hardware in the gas stand and the calibration of the GT Power model developed is described. The calibration leverages data coming from the tests on a 2 cylinder 2-stroke 0.73L diesel engine. The initial flow bench results suggested the need for a revision of the turbo matching due to the big gap in performance between predicted maps and real data. This activity was performed using Honeywell turbocharger solutions spacing from fixed geometry waste gate to variable nozzle turbo (VNT).

The reduction of particulate emissions is one of the most important challenges facing the development of future gasoline engines. Several studies have demonstrated the impact of fuel chemical composition on the emissions of particulate matter, more particularly, the detrimental effect of high boiling point components such as heavy aromatics. Fuel contamination is likely to become a critical issue as new regulations such as Real Driving Emissions RDE involves the use of market fuel. The objective of this study is to investigate several experimental approaches to detect the presence of Diesel contamination in Gasoline which is likely to alter pollutant emissions. To achieve this, a fuel matrix composed of 12 fuels was built presenting diesel fuel in varying concentrations from 0.1 to 2% v/v. The fuel matrix was characterized using several original techniques developed in this study.

Dilution is a promising way to improve fuel economy of Spark-Ignited (SI) gasoline engines. In this context, influence of innovative ignition systems on the dilution acceptance of a 400cc optical GDI engine has been studied. Several systems were tested and compared to a conventional coil: a dual-coil system and two nanosecond scaled plasma generators. Two operating points were studied: 2.8bar IMEP (net) at 2000rpm and 9bar IMEP (net) at 1200rpm. Two diluents were evaluated: real EGR and air (lean combustion). High-speed imaging at frequency up to 10kHz was performed to visualize both spark and combustion initiation and propagation. Voltage and current were measured to infer the energy deposited in the spark plug gap. The dual-coil DCO™ system and the nanosecond multi-pulse plasma generator at their maximum power showed an ability to extend the dilution range of the engine.

Knock in spark ignition engines is stochastic in nature. It is caused by autoignition in hot spots in the unburned end-gas ahead of the expanding flame front. Knock onset in an engine cycle can be predicted using the Livengood-Wu integral if the variation of ignition delay with pressure and temperature as well as the pressure and temperature variation with crank angle are known. However, knock intensity (KI) is determined by the evolution of the pressure wave following knock onset. In an earlier paper (SAE 2017-01-0689) we showed that KI can be approximated by KI = Z (∂T/∂x)-2 at a fixed operating condition, where Z is a function of Pko, the pressure, and (∂T/∂x) is the temperature gradient in the hot spot at knock onset. Then, from experimental measurements of KI and Pko, using five different fuels, with the engine operating at boosted conditions, a probability density function for (∂T/∂x) was established.

Pre-chamber combustion (PCC) is a promising engine combustion concept capable of extending the lean limit at part load. The engine experiments in the literature showed that the PCC could achieve higher engine thermal efficiency and much lower NOx emission than the spark-ignition engine. Improved understanding of the detailed flow and combustion physics of PCC is important for optimizing the PCC combustion. In this study, we investigated the gas exchange and flame jet from a narrow throat pre-chamber (PC) by only fueling the PC with methane in an optical engine. Simultaneous negative acetone planar laser-induced fluorescence (PLIF) imaging and OH* chemiluminescence imaging were applied to visualize the PC jet and flame jet from the PC, respectively. Results indicate a delay of the PC gas exchange relative to the built-up of the pressure difference (△ P) between PC and the main chamber (MC). This should be due to the gas inertia inside the PC and the resistance of the PC nozzle.

Reduction of CO2 emissions is becoming one of the great challenges for future gasoline engines. Downsizing is one of the most promising strategies to achieve this reduction, though it facilitates occurrence of knocking. Therefore, downsizing has to be associated with knock limiting technologies. The aim of the current research program is to adapt the fuel Research-Octane-Number (RON) injected in the combustion chamber to prevent knock occurrence and keep combustion phasing at optimum. This is achieved by a dual fuel injection strategy, involving a low-RON naphtha-based fuel (Naphtha, RON 71) and a high-RON octane booster (Ethanol, RON107). The ratio of fuel quantity on each injector is adapted to fit the RON requirement as a function of engine operating conditions. Hence, it becomes crucial to understand and predict the mixture preparation, to quantify its spatial and cycle-to-cycle variations and to apprehend the consequences on combustion behavior - knock especially.

Air traffic has been steadily increasing for the last years. Moreover, fuel availability at a reasonable cost seems more and more uncertain. Climate change implies that greenhouse gases emissions should be reduced. In this context, the search for new alternative fuels for aircraft seems to be a promising solution. Nevertheless, aeronautic represents a very specific transportation mode, due to its usage (short range, middle range, long range with the same fuel, worldwide distribution of the fuel…) and its compulsory security constraints. In the first part of the European project ALFA-BIRD (Alternative Fuels and Biofuels for Aircraft development - FP7), a selection of the best candidates to become the fuels for the future of aircraft has been done. The selection process was very complex, due to multiple criteria (physical properties, economical issued, environmental issues…).

Toluene primary reference fuel (TPRF) (mixture of toluene, iso-octane and heptane) is a suitable surrogate to represent a wide spectrum of real fuels with varying octane sensitivity. Investigating different surrogates in engine simulations is a prerequisite to identify the best matching mixture. However, running 3D engine simulations using detailed models is currently impossible and reduction of detailed models is essential. This work presents an AramcoMech reduced kinetic model developed at King Abdullah University of Science and Technology (KAUST) for simulating complex TPRF surrogate blends. A semi-decoupling approach was used together with species and reaction lumping to obtain a reduced kinetic model. The model was widely validated against experimental data including shock tube ignition delay times and premixed laminar flame speeds. Finally, the model was utilized to simulate the combustion of a low reactivity gasoline fuel under partially premixed combustion conditions.

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 pre-chamber combustion (PCC) concept is a proven lean or diluted combustion technique for internal combustion engines with benefits in engine efficiency and reduced NOx emissions. The engine lean operation limit can be extended by supplying auxiliary fuel into the pre-chamber and thereby, achieving mixture stratification inside the pre-chamber over the main chamber. Introducing liquid fuels into the pre-chambers is challenging owing to the small form factor of the pre-chamber. With a conventional injector, the fuel penetrates in liquid form and impinges on the pre-chamber walls, which leads to increased unburned hydrocarbon emissions from the pre-chamber. In this study, a prototype liquid fuel injector is introduced which preheats the fuel within a heated chamber fitted with an electrical heating element before injecting an effervescently atomized spray into the pre-chamber.

Accurately predicting the future behavior of the surrounding traffic, especially the velocity of the lead vehicle is important for optimizing the energy consumption and improve the safety of Connected and Automated Vehicles (CAVs). Several studies report methods to predict short-to-mid-length lead vehicle velocity using stochastic models or other data-driven techniques, which require availability of extensive data and/or Vehicle-to-Vehicle (V2V) communication. In the absence of connectivity, or in data-restricted cases, the prediction must rely only on the measured position and relative velocity of the lead vehicle at the current time. This paper proposes two velocity predictors to predict short-to-mid-length lead vehicle velocity. The first predictor is based on a Constant Acceleration (CA) with an augmented stop mode. The second one is based on a modified Enhanced Driver Model (EDM-LOS) with line-of-sight feature.

Recent work has demonstrated the potential of gasoline-like fuels to reduce NOX and particulates emissions when used in diesel engines. Indeed, fuels highly resistant to auto-ignition provide more time for fuel and air mixing prior to the combustion and therefore a more homogeneous combustion. Nevertheless, major issues still need to be addressed, particularly regarding UHC and CO emissions at low load and particulate/noise combustion trade-off at high load. The purpose of this study is to investigate how an existing modern diesel engine could be operated with low-cetane fuels and define the most appropriate Cetane Number (CN) to reduce engine-out emissions. With this regard, a selection of naphtha and gasoline blends, ranging from CN30/RON 57 to CN35/RON 41 was investigated on a Euro 5, 1.6L four-cylinder engine. Results were compared to the conventional diesel running mode using a minimum NOX level oriented calibration, both in steady state and transient conditions.

Recent work has demonstrated the potential of gasoline-like fuels to reduce NOx and particulate emissions when used in Diesel engines. In this context, straight-run naphtha, a refinery stream directly derived from the atmospheric crude oil distillation process, has been identified as a highly valuable fuel. The current study is one step further toward naphtha-based fuel to power compression ignition engines. The potential of a cetane number 25 fuel (CN25), resulting from a blend of hydro-treated straight-run naphtha CN35 with unleaded non-oxygenated gasoline RON91 was assessed. For this purpose, investigations were conducted on multiple fronts, including experimental activities on an injection test bed, in an optically accessible vessel and in a single cylinder engine. CFD simulations were also developed to provide relevant explanations.

If fuels that are more resistant to auto-ignition are injected near TDC in compression ignition engines, they ignite much later than diesel fuel and combustion occurs when the fuel and air have had more chance to mix. This helps to reduce NOX and smoke emissions at much lower injection pressures compared to a diesel fuel. However, PPCI (Partially Premixed Compression Ignition) operation also leads to higher CO and HC at low loads and higher heat release rates at high loads. These problems can be significantly alleviated by managing the mixing through injector design (e.g. nozzle size and centreline spray angle) and changing CR (Compression Ratio). This work describes results of running a single-cylinder diesel engine on fuel blends by using three different nozzle design (nozzle size: 0.13 mm and 0.17 mm, centreline spray angle: 153° and 120°) and two different CRs (15.9:1 and 18:1).