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Technical Paper

On the HCCI octane boosting effects of γ-Valerolactone

2019-08-15
2019-24-0026
Transportation sector is almost entirely powered by internal combustion engines (ICEs) burning petroleum-based liquid fuels. This makes the transportation sector the main culprit of global warming due to the large quantity of CO2 emission from burning these petroleum-based fuels. Over the last few decades, there are growing concerns over global warming and diminishing petroleum reserves. Such concerns have led to concentrated efforts directed at a paradigm shift from conventional fuels to renewable alternatives which can promote cleaner combustion. Therefore, future research directions should orient towards exploring new fuels suitable for future ICEs to achieve better engine efficiency and significantly less harmful emissions. One way to achieve these objectives is to focus on improving the combustion technology by developing new fuel-engine systems. Consequently, scientists and engineers are showing growing interest towards non-petroleum-based fuels coming from renewable resources.
Technical Paper

Study of fuel octane sensitivity effects on gasoline partially premixed combustion using optical diagnostics

2019-08-15
2019-24-0025
Partially premixed combustion (PPC) is a low-temperature combustion (LTC) concept that could deliver higher engine efficiency, as well as lower NOx and soot emissions. Gasoline-like fuels are beneficial for air/fuel mixing process under PPC mode because they have superior auto-ignition resistance to prolong ignition delay time. In current experiments, the high octane number gasoline fuel E10 (US market used gasoline, RON=91) and low octane number GCI blend fuel (RON=77) were tested respectively in a full-transparent AVL single cylinder optical compression ignition (CI) engine. Aiming at investigating the fuel sensitivity on engine performances under different combustion modes as well as soot particle emissions, the engine operating parameters and emission data were analyzed from CI to HCCI (homogeneous charge compression ignition) via PPC (partially premixed combustion) by changing fuel injection timing.
Technical Paper

A Study of Lean Burn Pre-chamber Concept in a Heavy Duty Engine

2019-08-15
2019-24-0107
Due to stringent emission standards, the demand for higher efficiency engines has been unprecedentedly high in recent years. Among several existing combustion modes, pre-chamber initiated combustion emerges to be a potential candidate for high-efficiency engines. Research on the pre-chamber concept exhibit higher indicated efficiency through lean limit extension while maintaining the combustion stability. In this study, different pre-chamber geometries were tested in a single-cylinder heavy-duty engine at different loads. The geometries were prepared with three different pre-chamber volumes and with three varying nozzle area to pre-chamber volume ratios. The pre-chambers were fueled with methane while two sets of experiments were conducted, the first with ethanol as main chamber fuel and the second with methane.
Technical Paper

Compression Ratio and Intake Air Temperature Effect on the Fuel Flexibility of Compression Ignition Engine

2019-08-15
2019-24-0110
The effect of compression ratio and intake air temperature on the combustion characteristics of fuels with different octane ratings were investigated on a single-cylinder heavy-duty engine. The study examined Primary Reference Fuels (PRFs) and commercial grade diesel with octane numbers that range from 0 to 100. The engine was configured at a lower compression ratio (CR) of 11.5:1 than typical heavy-duty CI engines to compare the fuels’ burning regime with recently reported measurements at CR17:1. Experiments were performed at different intake air temperature of 20 to 80 DegC, intake air pressure of 1.5 to 3 bar absolute, net indicated mean effective pressure (IMEPNet) of 5 to 20 bar, air/fuel equivalence ratio (lambda) of 1.7 to 3.5, and fuel injection pressure of 700 to 1400 bar. The injection rates have been characterized to determine the hydraulic delay of the injector and thus define the actual ignition delay time.
Technical Paper

In Situ Spray Momentum Measurement with Fast Acting High-Pressure Solenoid HD Direct Injector Using Single and Multiple Injections Events on Internal Combustion Engine.

2019-08-15
2019-24-0136
High-pressure isobaric combustion is a potential pathway toward high-efficiency Internal Combustion (IC) engines. The multi injections strategy with current technology is capable of controlling the Heat Release Rate (HRR) needed in such configuration. This implies the use of multiple split-injections with relatively very short dwell duration. This paper investigates the behavior of a high-flow-rate solenoid injector operating with single and split injections. The spray momentum is measured while the injector is mounted on the engine and connected to the in-series fuel system. This method provides a more realistic injection pressure compared to conventional injection rate dedicated rigs. A high natural frequency piezoelectric pressure transducer is mounted at 4 mm in front of the nozzle hole with an adjustable angle. The injector and sensor are contained to collect the injected fuel.
Technical Paper

Heat Loss Investigation of Multiple Injectors CI Concepts

2019-08-15
2019-24-0172
Towards the goal of high efficiency, heat losses through the cylinder walls need to be reduced for heavy-duty CI engines. This study proposes the use of multiple injectors to overcome this issue. Comparisons of one, two and three injectors’ utilizations are performed with optical and metal engines as well as CFD studies. Furthermore, a flat bowl is compared to the standard bowl in terms of performance and heat losses. It has earlier been proven that the distance from injector to the wall is significant in terms of heat loss reduction. A flat bowl increases this distance, and is thus, together with a smaller surface area, expected to reduce heat losses. Performance measures from the metal experiments proved the benefits of multiple injectors in terms of heat loss reduction and efficiency gain. The flat bowl further reduced the heat losses without adventuring the mixing capabilities. From the optical experiments, the spray and flame movements were evaluated.
Technical Paper

Oxy-fuel HCCI combustion in a CFR engine with carbon dioxide as a thermal buffer

2019-08-15
2019-24-0119
A basic formula inspired by the Otto engine cycle shows that the thermodynamic efficiency of the engine increases as the mixture specific heat ratio and compression ratio increase. Homogenous charge compression ignition (HCCI) engines allow the combustion of a lean mixture at relatively higher compression ratios increasing the thermodynamic efficiency. At the same time, it is also a low temperature combustion and this means lower NOx emissions. One way to increase the thermodynamic efficiency of the engine is to increase the specific heat ratio by replacing the nitrogen in the oxidizer by a monoatomic gas that has the highest possible specific heat ratio. However, higher specific heat ratio results in elevated cylinder temperature and pressure leading to engine knock. The compression ratio is thus decreased to avoid this phenomenon. Also, elevated engine temperature will oxidize any nitrogen (no matter how small) forming undesired NOx emissions.
Technical Paper

Novel Geometry Reaching High Efficiency for Multiple Injector Concepts

2019-04-02
2019-01-0246
Heat losses are known to decrease the efficiency of CI engines largely. Here, multiple injectors have been suggested to shrink these losses through reduction of spray wall impingement. Studies on multiple injectors have proven the concept’s heat transfer reduction but also highlighted the difficulty of using a standard piston bowl. This study proposes a two-injector concept combined with a flat bowl to reduce heat losses further. To change the spray pattern, the two injectors are injecting in a swirling motion while placed at the rim of the bowl. Four injection timings have been investigated using Reynolds-Averaged Navier-Stokes simulations. This computational method quantified the amount of heat loss reduction possible. A conventional single injector concept is compared to two injector concepts with a standard and flat bowl. A Double Compression Expansion Engine (DCEE) concept, based on a modified Volvo D13 single-cylinder engine, was the base for all simulations.
Technical Paper

HCCI Octane Number Scale in a Pressure-Temperature Diagram

2019-04-02
2019-01-0965
A new approach for investigating combustion behavior of practical fuels under homogeneous charge compression ignition (HCCI) conditions was developed with the help of a cooperative fuel research (CFR) engine. The method uses a set of two pressure-temperature diagrams and two charts, each with an octane number scale based on primary reference fuels (PRF), created from experimental results by sweeping the intake temperature. The two pressure-temperature diagrams report conditions leading to the start of the low temperature combustion and the start of the main combustion, respectively. Additional two charts -- required compression ratio and fraction of low temperature heat release charts -- describe global combustion behavior and the importance of the low temperature combustion. Each diagram and chart, together with their respective octane number scale, allow to examine the combustion behavior of practical fuels by comparing their combustion behavior with those of the PRFs.
Technical Paper

Variable Compression Ratio (VCR) Piston - Design Study

2019-04-02
2019-01-0243
Variable compression ratio (VCR) technology has long been recognized as a method for improving the automobile engine performance, efficiency, fuel economy with reduced emission. This paper presents a design of hydraulically actuated piston based on the VCR piston proposed by the British Internal Combustion Engine Research Institute (BICERI). In this design, the compression height of the piston automatically changes in response to engine cylinder pressure by controlling the lubrication oil flow via valves in the piston. In addition, numerical models including piston kinetic model, oil hydraulic model, compression ratio model and etc., have been established to evaluate the piston properties. The oil flow characteristics between two chambers in VCR piston have been investigated and the response behaviors of VCR engine and normal engine, such as compression pressure and peak cylinder pressure, are compared at different engine loads.
Technical Paper

A Path towards High Efficiency Using Argon in an HCCI Engine

2019-04-02
2019-01-0951
Argon replacing Nitrogen has been examined as a novel engine cycle reaching higher efficiency. Experiments were carried out under Homogeneous Charge Compression Ignition (HCCI) conditions using a single cylinder variable compression ratio Cooperative Fuel Research (CFR) engine. Isooctane has been used as the fuel for this study. All the parameters were kept fixed but the compression ratio to make the combustion phasing constant. Typical engine outputs and emissions were compared to conventional cycles with both air and synthetic air. It has been found that the compression ratio of the engine must be significantly reduced while using Argon due to its higher specific heat ratio. The resulting in-cylinder pressure was lower but combustion remains aggressive. However, greater in-cylinder temperatures were reached. To an end, Argon allows gains in fuel efficiency, in unburned hydrocarbon and carbon monoxide, as well as in indicated efficiency.
Technical Paper

Should We Walk or Take a Car for Minimum Greenhouse Gas Emissions?

2019-04-02
2019-01-0996
This paper compares the greenhouse gas (GHG) emissions attributed to driving a popular production vehicle powered by an internal combustion engine (ICE), as well as a hybrid electric vehicle (HEV), with GHG emissions associated with walking, running and bicycling. The purpose of this study is to offer a different perspective on the problem of global warming due to anthropogenic causes, specifically on transportation and eating patterns. In order to accurately estimate emissions, a full life cycle of food has been considered coupled with energy expenditures of the aforementioned activities obtained from several different sources and averaged for more reliable results. The GHG emissions were calculated for Sweden, the UK, and the US. Depending on the availability of certain data, the methodology for different countries was altered slightly. The question whether walking, running or taking a bicycle is better for the environment than driving a car cannot be answered uniquely.
Technical Paper

Combustion Stratification and Dynamic Flame Tracing Analysis of Partially Premixed Combustion in a Compression Ignition Engine Fueled with Low-Octane Fuel

2019-04-02
2019-01-1151
Partially premixed combustion (PPC) is a low-temperature combustion concept, which is between conventional diesel compression ignition (CI) and homogeneous charge compression ignition (HCCI). In PPC mode, the start of injection timing (SOI) is earlier than that of CI and later than that of HCCI and stratified in-cylinder fuel/air mixture can be formed to control the auto-ignition by the fuel injection timing. Gasoline fuel is beneficial for PPC mode because of its superior resistance to auto-ignition, which can enhance fuel-air charge mixing process with longer ignition delay time. The scope of this study is to investigate in-cylinder auto-ignition, combustion evolution, combustion stratification, and engine-out emissions at PPC operating mode under lean and low load engine conditions with different injection timings. Primary reference fuel PRF77, was selected as the low-octane test fuel.
Technical Paper

The Physical and Chemical Effects of Fuel on Gasoline Compression Ignition

2019-04-02
2019-01-1150
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.
Technical Paper

CFD Study of Heat Transfer Reduction Using Multiple Injectors in a DCEE Concept

2019-01-15
2019-01-0070
Earlier studies on efficiency improvement in CI engines have suggested that heat transfer losses contribute largely to the total energy losses. Fuel impingement on the cylinder walls is typically associated with high heat transfer. This study proposes a two-injector concept to reduce heat losses and thereby improve efficiency. The two injectors are placed at the rim of the bowl to change the spray pattern. Computational simulations based on the Reynolds-Averaged Navier-Stokes approach have been performed for four different fuel injection timings in order to quantify the reduction in heat losses for the proposed concept. Two-injector concepts were compared to reference cases using only one centrally mounted injector. All simulations were performed in a double compression expansion engine (DCEE) concept using the Volvo D13 single-cylinder engine. In the DCEE, a large portion of the exhaust energy is re-used in the second expansion, thus increasing the thermodynamic efficiency.
Technical Paper

Isobaric Combustion: A Potential Path to High Efficiency, in Combination with the Double Compression Expansion Engine (DCEE) Concept

2019-01-15
2019-01-0085
The efficiency of an internal combustion engine is highly dependent on the peak pressure at which the engine operates. A new compound engine concept, the double compression expansion engine (DCEE), utilizes a two-stage compression and expansion cycle to reach ultrahigh efficiencies. This engine takes advantage of its high-integrity structure, which is adapted to high pressures, and the peak motored pressure reaches up to 300 bar. However, this makes the use of conventional combustion cycles, such as the Seiliger-Sabathe (mixed) or Otto (isochoric) cycles, not feasible as they involve a further pressure rise due to combustion. This study investigates the concept of isobaric combustion at relatively high peak pressures and compares this concept with traditional diesel combustion cycles in terms of efficiency and emissions. Multiple consecutive injections through a single injector are used for controlling the heat release rate profile to achieve isobaric heat addition.
Technical Paper

Compression Ignition of Low Octane Gasoline under Partially Premixed Combustion Mode

2018-09-10
2018-01-1797
Partially premixed combustion (PPC) is an operating mode that lies between the conventional compression ignition (CI) mode and homogeneous charge compression ignition (HCCI) mode. The combustion in this mixed mode is complex as it is neither diffusion-controlled (CI mode) nor governed solely by chemical kinetics (HCCI mode). In this study, CFD simulations were performed to evaluate flame index, which distinguishes between zones having a premixed flame and non-premixed flame. Experiments performed in the optical engine supplied data to validate the model. In order to realize PPC, the start of injection (SOI) was fixed at −40 CAD (aTDC) so that a required ignition delay is created to premix air/fuel mixture. The reference operating point was selected to be with 3 bar IMEP and 1200 rpm. Naphtha with a RON of 77 and its corresponding PRF surrogate were tested. The simulations captured the general trends observed in the experiments well.
Technical Paper

Blending Octane Number of 1-Butanol and Iso-Octane with Low Octane Fuels in HCCI Combustion Mode

2018-09-10
2018-01-1681
Due to their physical and chemical properties, alcohols such as ethanol and methanol when blended with gasoline provide high anti-knock quality and hence efficient engines. However, there are few promising properties of 1-butanol similar to conventional gasoline which make it a favorable choice for internal combustion engines. Previously the author showed that by blending ethanol and methanol with low octane fuels, non-linear increase in the HCCI fuel number occurs in HCCI combustion mode. Very few studies have been conducted on the use of 1-butanol in HCCI combustion mode, therefore for this work, 1-butanol with a RON 96 was selected as the high octane fuel. Three low octane fuels with octane number close to 70 were used as a base fuel. Two of the low octane fuels are Fuels for Advanced Combustion Engines (FACE gasolines), more specifically FACE I and FACE J and also primary reference fuel (PRF 70) were selected.
Technical Paper

Combustion Behavior of n-Heptane, Isooctane, Toluene and Blends under HCCI Conditions in the Pressure-Temperature Diagram

2018-09-10
2018-01-1684
Homogeneous charge compression ignition (HCCI) experiments were run with the aid of a Cooperative fuel research (CFR) engine, operating at 600 rpm and under very lean conditions (ϕ = 0.3). This study seeks to examine the combustion behavior of different fuels by finding the pressure-temperature (p-t) conditions that instigate the start of combustion, and the transition from low temperature combustion to principal combustion. The pressure-temperature diagram emphasizes p-t conditions according to their traces through the compression stroke. In each fuel tested, p-t traces were examined by a sweep of the intake temperature; and for each experimental point, combustion phasing was maintained at top dead center by adjusting the compression ratio of the engine. In addition to the p-t diagram, results were analyzed using a compression ratio-intake temperature diagram, which showed the compression ratio required with respect to intake temperature.
Technical Paper

Investigation of Premixed and Diffusion Flames in PPC and CI Combustion Modes

2018-04-03
2018-01-0899
The experimental in-cylinder combustion process was compared with the numerical simualtion for naphtha fuel under conventional compression ignition (CI) and partially premixed combustion (PPC) conditions. The start of injection timing (SOI) with the single injection strategy was changed from late of −10 CAD aTDC to early of −40 CAD aTDC. The three-dimensional full cycle engine combustion simulation was performed coupling with gas phase chemical kinetics by the CFD code CONVERGE™. The flame index was used for evaluating the combustion evolution of premixed flame and diffusion flame. The results show that the flame index could be used as an indicator for in-cylinder homogeneity evaluation. Hydroperoxyl shows a similar distribution with the premixed combustion. Formaldehyde could be used as an indicator for low temperature combustion.
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