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Technical Paper

Axial Flow Turbine Concept for Conventional and e-Turbocharging

2019-09-09
2019-24-0185
Engine downsizing has established itself as one of the most successful strategies to reduce fuel consumption and pollutant emissions in the automotive field. To this regard, a major role is played by turbocharging, which allows an increase in engine power density, so reducing engine size and weight. However, the need for turbocharging imposes some issues to be solved. In the attempt of mitigating turbo lag and poor low-end torque, many solutions have been presented in the open literature so far, such as: low inertia turbine wheels and variable geometry turbines; or even more complex concepts such as twin turbo and electrically assisted turbochargers. None of them appears as definitive, though. As a possible way of reducing turbine rotor inertia, and so the turbo lag, also the change of turbine layout has been investigated, and it revealed itself to be a viable option, leading to the use of mixed-flow turbines.
Technical Paper

Experimental Investigation of Combustion and Emission Characteristics of Stoichiometric Stratified Flame Ignited (SFI) Hybrid Combustion in a 4-Stroke PFI/DI Gasoline Engine

2019-04-02
2019-01-0960
Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), can improve the fuel economy of gasoline engines and simultaneously achieve ultra-low NOx emissions. However, the difficulty in combustion phasing control and violent combustion at high loads limit the commercial application of CAI combustion. To overcome these problems, stratified mixture, which is rich around the central spark plug and lean around the cylinder wall, is formed through port fuel injection and direct injection of gasoline. In this condition, rich mixture is consumed by flame propagation after spark ignition, while the unburned lean mixture auto-ignites due to the increased in-cylinder temperature during flame propagation, i.e., stratified flame ignited (SFI) hybrid combustion.
Technical Paper

Dilution Boundary Expansion Mechanism of SI-CAI Hybrid Combustion Based on Micro Flame Ignition Strategy

2019-04-02
2019-01-0954
In decade years, Spark Ignition-Controlled Auto Ignition (SI-CAI) hybrid combustion, also called Spark Assisted Compression Ignition (SACI) has shown its high-efficiency and low emissions advantages. However, high dilution causes the problem of unstable initial ignition and flame propagation, which leads to high cyclic variation of heat release and IMEP. The instability of SI-CAI hybrid combustion limits its dilution degree and its ability to improve the thermal efficiency. In order to solve instability problems and expand the dilution boundary of hybrid combustion, micro flame ignition (MFI) strategy is applied in gasoline hybrid combustion engines. Small amount of Dimethyl Ether (DME) chosen as the ignition fuel is injected into cylinder to form micro flame kernel, which can stabilize the ignition combustion process.
Technical Paper

The Application of Controlled Auto-Ignition Gasoline Engines -The Challenges and Solutions

2019-04-02
2019-01-0949
Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to simultaneously reduce the fuel consumption and nitrogen oxides emissions of gasoline engines. However, narrow operating region in loads and speeds is one of the challenges for the commercial application of CAI combustion to gasoline engines. Therefore, the extension of loads and speeds is an important prerequisite for the commercial application of CAI combustion. The effect of intake charge boosting, charge stratification and spark-assisted ignition on the operating range in CAI mode was reviewed. Stratified flame ignited (SFI) hybrid combustion is one form to achieve CAI combustion under the conditions of highly diluted mixture caused by the flame in the stratified mixture with the help of spark plug.
Technical Paper

Simulation of the Effect of Intake Pressure and Split Injection on Lean Combustion Characteristics of a Poppet-Valve Two-Stroke Direct Injection Gasoline Engine at High Loads

2018-09-10
2018-01-1723
Poppet-valve two-stroke gasoline engines can increase the specific power of their four-stroke counterparts with the same displacement and hence decrease fuel consumption. However, knock may occur at high loads. Therefore, the combustion with stratified lean mixture was proposed to decrease knock tendency and improve combustion stability in a poppet-valve two-stroke direct injection gasoline engine. The effect of intake pressure and split injection on fuel distribution, combustion and knock intensity in lean mixture conditions at high loads was simulated with a three-dimensional computational fluid dynamic software. Simulation results show that with the increase of intake pressure, the average fuel-air equivalent ratio in the cylinder decreases when the second injection ratio was fixed at 70% at a given amount of fuel in a cycle.
Technical Paper

Study of Flame Speed and Knocking Combustion of Gasoline, Ethanol and Hydrous Ethanol (10% Water) at Different Air/Fuel Ratios with Port-Fuel Injection

2018-04-03
2018-01-0655
In this paper, an experimental study was performed to investigate characteristics of flame propagation and knocking combustion of hydrous (10% water content) and anhydrous ethanol at different air/fuel ratios in comparison to RON95 gasoline. Experiments were conducted in a full bore overhead optical access single cylinder port-fuel injection spark-ignition engine. High speed images of total chemiluminescence and OH* emission was recorded together with the in-cylinder pressure, from which the heat release data were derived. The results show that under the stoichiometric condition anhydrous ethanol and wet ethanol with 10% water (E90W10) generated higher IMEP with at an ignition timing slightly retarded from MBT than the gasoline fuel for a fixed throttle position. Under rich and stoichiometric conditions, the knock limited spark timing occurred at 35 CA BTDC whereas both ethanol and E90W10 were free from knocking combustion at the same operating condition.
Technical Paper

Experimental Investigation of Combustion and Emission Characteristics of the Direct Injection Dimethyl Ether Enabled Micro-Flame Ignited (MFI) Hybrid Combustion in a 4-Stroke Gasoline Engine

2018-04-03
2018-01-1247
Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to improve gasoline engines’ efficiency and simultaneously achieve ultra-low NOx emissions. Two of the primary obstacles for applying CAI combustion are the control of combustion phasing and the maximum heat release rate. To solve these problems, dimethyl ether (DME) was directly injected into the cylinder to generate multi-point micro-flame through compression in order to manage the entire heat release of gasoline in the cylinder through port fuel injection, which is known as micro-flame ignited (MFI) hybrid combustion.
Technical Paper

Numerical Simulation of the Gasoline Spray with an Outward-Opening Piezoelectric Injector: A Comparative Study of Different Breakup Models

2018-04-03
2018-01-0272
The outward-opening piezoelectric injector can achieve stable fuel/air mixture distribution and multiple injections in a single cycle, having attracted great attentions in direct injection gasoline engines. In order to realise accurate predictions of the gasoline spray with the outward-opening piezoelectric injector, the computational fluid dynamic (CFD) simulations of the gasoline spray with different droplet breakup models were performed in the commercial CFD software STAR-CD and validated by the corresponding measurements. The injection pressure was fixed at 180 bar, while two different backpressures (1 and 10 bar) were used to evaluate the robustness of the breakup models. The effects of the mesh quality, simulation timestep, breakup model parameters were investigated to clarify the overall performance of different breakup model in modeling the gasoline sprays.
Technical Paper

Potentials of External Exhaust Gas Recirculation and Water Injection for the Improvement in Fuel Economy of a Poppet Valve 2-Stroke Gasoline Engine Equipped with a Two-Stage Serial Charging System

2018-04-03
2018-01-0859
Engine downsizing is one of the most effective means to improve the fuel economy of spark ignition (SI) gasoline engines because of lower pumping and friction losses. However, the occurrence of knocking combustion or even low-speed pre-ignition at high loads is a severe problem. One solution to significantly increase the upper load range of a 4-stroke gasoline engine is to use 2-stroke cycle due to the double firing frequency at the same engine speed. It was found that a 0.7 L two-cylinder 2-stroke poppet valve gasoline engine equipped with a two-stage serial boosting system, comprising a supercharger and a downstream turbocharger, could replace a 1.6 L naturally aspirated 4-stroke gasoline engine in our previous research, but its fuel economy was close to that of the 4-stroke engine at upper loads due to knocking combustion.
Technical Paper

Influence of Biodiesel Blending on Particulate Matter (PM) Oxidation Characteristics

2017-03-28
2017-01-0932
The use of diesel particulate filter [DPF] has become a standard in modern diesel engine after treatment technology. However pressure drop develops across the filter as PM accumulates and this requires quick periodic burn-out without incurring thermal runaway temperatures that could compromise DPF integrity during operation. Adequate understanding of soot oxidation is needed for design and manufacture of efficient filter traps for the engine system. In this study, we have examined the impact of blending biodiesel on oxidation of PM generated from a high speed direct injection [HSDI] diesel engine, which was operated with 20% [B20] and 40% [B40] blends of two biodiesel fuels. The PM samples were collected from the engine exhaust using a Pall Tissuquartz filter, the oxidation characteristics of the samples were carried out using thermogravimetric analyzer [TGA]. The biodiesel oxidation data obtained from pure petrodiesel was compared against the fuel blends.
Technical Paper

Reduction of Methane Slip Using Premixed Micro Pilot Combustion in a Heavy-Duty Natural Gas-Diesel Engine

2015-09-01
2015-01-1798
An experimental study has been carried out with the end goal of minimizing engine-out methane emissions with Premixed Micro Pilot Combustion (PMPC) in a natural gas-diesel Dual-Fuel™ engine. The test engine used is a heavy-duty single cylinder engine with high pressure common rail diesel injection as well as port fuel injection of natural gas. Multiple variables were examined, including injection timings, exhaust gas recirculation (EGR) percentages, and rail pressure for diesel, conventional Dual-Fuel, and PMPC Dual-Fuel combustion modes. The responses investigated were pressure rise rate, engine-out emissions, heat release and indicated specific fuel consumption. PMPC reduces methane slip when compared to conventional Dual-Fuel and improves emissions and fuel efficiency at the expense of higher cylinder pressure.
Technical Paper

Experimental Investigation on DME Assisted Gasoline CAI/HCCI Combustion with Intake Re-Breathing Valve Strategy

2015-09-01
2015-01-1818
In order to investigate feasibility of DME (Di-methyl ether) assisted gasoline CAI (controlled-auto ignition) combustion, direct DME injection is employed to act as the ignition source to trigger the auto-ignition combustion of premixed gasoline/air mixture with high temperature exhaust gas. Intake re-breathing valve strategy is adopted to obtain internal exhaust recirculation (EGR) that regulates heat release rate and ignitability of the premixed gasoline and air mixture. The effects of intake re-breathing valve timing and 2nd DME injection timing of different split injection ratios were investigated and discussed in terms of combustion characteristics, emission and efficiencies. The analyses showed that re-breathing intake valve timing had a large effect on the operation range of CAI combustion due to EGR and intake temperature variation.
Technical Paper

Comparison of Performance, Efficiency and Emissions between Gasoline and E85 in a Two-Stroke Poppet Valve Engine with Lean Boost CAI Operation

2015-04-14
2015-01-0827
Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Most research on CAI/HCCI combustion operations have been carried out in 4-stroke gasoline engines, despite it was originally employed to improve the part-load combustion and emission in the two-stroke gasoline engine. However, conventional ported two-stroke engines suffer from durability and high emissions. In order to take advantage of the high power density of the two-stroke cycle operation and avoid the difficulties of the ported engine, systematic research and development works have been carried out on the two-stroke cycle operation in a 4-valves gasoline engine. CAI combustion was achieved over a large range of operating conditions when the relative air/fuel ratio (lambda) was kept at one as measured by an exhaust lambda sensor.
Technical Paper

Effects of Ethanol on Part-Load Performance and Emissions Analysis of SI Combustion with EIVC and Throttled Operation and CAI Combustion

2014-04-01
2014-01-1611
Internal combustion engines are subjected to part-load operation more than in full load during a typical vehicle driving cycle. The problem with the Spark Ignition (SI) engine is its inherent low part-load efficiency. This problem arises due to the pumping loses that occur when the throttle closes or partially opens. One way of decreasing the pumping losses is to operate the engine lean or by adding residual gases. It is not possible to operate the engine unthrottled at very low loads due to misfire. However, the load can also be controlled by changing the intake valve closing timing - either early or late intake valve closing. Both strategies reduce the pumping loses and hence increase the efficiency. However the early intake valve closure (EIVC) can be used as mode transition from SI to CAI combustion.
Technical Paper

2-Stroke CAI Operation on a Poppet Valve DI Engine Fuelled with Gasoline and its Blends with Ethanol

2013-04-08
2013-01-1674
Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Currently, CAI combustion is constrained at part load operation conditions because of misfire at low load and knocking combustion at high load, and the lack of effective means to control the combustion process. Extending its operating range including high load boundary towards full load and low load boundary towards idle in order to allow the CAI engine to meet the demand of whole vehicle driving cycles, has become one of the key issues facing the industrialisation of CAI/HCCI technology. Furthermore, this combustion mode should be compatible with different fuels, and can switch back to conventional spark ignition operation when necessary. In this paper, the CAI operation is demonstrated on a 2-stroke gasoline direct injection (GDI) engine equipped with a poppet valve train.
Technical Paper

Analysis of Gaseous and PM Emissions of 4-Stroke CAI/HCCI and SI Combustion in a DI Gasoline Engine

2013-04-08
2013-01-1549
Direct injection gasoline engines have the potential for improved fuel economy through principally the engine down-sizing, stratified charge combustion, and Controlled Auto Ignition (CAI). However, due to the limited time available for complete fuel evaporation and the mixing of fuel and air mixture, locally fuel rich mixture or even liquid fuel can be present during the combustion process of a direct injection gasoline engine. This can result in significant increase in UHC, CO and Particulate Matter (PM) emissions from direct injection gasoline engines which are of major concerns because of the environmental and health implications. In order to investigate and develop a more efficient DI gasoline engine, a camless single cylinder DI gasoline engine has been developed. Fully flexible electro-hydraulically controlled valve train was used to achieve spark ignition (SI) and Controlled Autoignition (CAI) combustion in both 4-stroke and 2-stroke cycles.
Technical Paper

Effects of Mechanical Turbo Compounding on a Turbocharged Diesel Engine

2013-03-25
2013-01-0103
This paper presents the simulation study on the effects of mechanical turbo-compounding on a turbocharged diesel engine. A downstream power-turbine has been coupled to the exhaust manifold after the main turbocharger, in the aim to recover waste heat energy. The engine in the current study is Scania DC13-06, which 6 cylinders and 13 litre in capacity. The possibilities, effectiveness and working range of the turbo compounded system were analyzed in this study. The system was modeled in AVL BOOST, which is a one dimensional (1D) engine code. The current study found that turbo compounding could possibly recover on average 11.4% more exhaust energy or extra 3.7kW of power. If the system is mechanically coupled to the engine, it could increase the average engine power by up to 1.2% and improve average BSFC by 1.9%.
Book

Laser Diagnostics and Optical Measurement Techniques in Internal Combustion Engines

2012-07-30
The increasing concern about CO2 emissions and energy prices has led to new CO2 emission and fuel economy legislation being introduced in world regions served by the automotive industry. In response, automotive manufacturers and Tier-1 suppliers are developing a new generation of internal combustion (IC) engines with ultra-low emissions and high fuel efficiency. To further this development, a better understanding is needed of the combustion and pollutant formation processes in IC engines. As efficiency and emission abatement processes have reached points of diminishing returns, there is more of a need to make measurements inside the combustion chamber, where the combustion and pollutant formation processes take place. However, there is currently no good overview of how to make these measurements.
Video

2-Stroke CAI Combustion Operation in a GDI Engine with Poppet Valves

2012-06-18
In order to extend the CAI operation range in 4-stroke mode and maximize the benefit of low fuel consumption and emissions in CAI mode, 2-stroke CAI combustion is revived operating in a GDI engine with poppet valves, where the conventional crankcase scavenging is replaced by boosted scavenging. The CAI combustion is achieved through the inherence of the 2-Stroke operation, which is retaining residual gas. A set of flexible hydraulic valve train was installed on the engine to vary the residual gas fraction under the boosting condition. The effects of spark timing, intake pressure and short-circuiting on 2-stroke CAI combustion and its emissions are investigated and discussed in this paper. Results show the engine could be controlled to achieve CAI operation over a wide range of engine speed and load in the 2-stroke mode because of the flexibility of the electro-hydraulic valvetrain system. Presenter Yan Zhang, Brunel University
Technical Paper

Experimental Study on Spark Assisted Compression Ignition (SACI) Combustion with Positive Valve Overlap in a HCCI Gasoline Engine

2012-04-16
2012-01-1126
The spark-assisted compression ignition (SACI) is widely used to expend the high load limit of homogeneous charge compression ignition (HCCI), as it can reduce the high heat release rate effectively while partially maintain the advantage of high thermal efficiency and low NOx emission. But as engine load increases, the SACI combustion traditionally using negative valve overlap strategy (NVO) faces the drawback of higher pumping loss and limited intake charge availability, which lead to a restricted load expansion and a finite improvement of fuel economy. In this paper, research is focused on the SACI combustion using positive valve overlap (PVO) strategy. The characteristics of SACI combustion employing PVO strategy with external exhaust gas recirculation (eEGR) are investigated. Two types of PVO strategies are analyzed and compared to explore their advantages and defects, and the rules of adjusting SACI combustion with positive valve overlap are concluded.
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