Simulation analysis of the effects of methanol-polyoxymethylene dimethyl ethers blends on combustion and emissions of a PCCI engine

The effects of methanol/polyoxymethylene dimethyl ethers (PODE) mixture with different blending ratios on premixed charge compression ignition (PCCI) combustion and emission performance have been researched through the anlysis of CFD software CONVERGE. Premixed combustion is achieved by a single early injection of fuel into the cylinder. The results show that the combustion start point delays and the peak pressure decreases with the increase of methanol blend ratio. The effects of injection timing on the combustion and emission characteristics of PCCI were studied by using a mixture of the same proportion of methanol. The results show that the advance of injection time leads to more homogeneous mixture and higher peak heat release. But too early injection reduces the temperature in the cylinder and makes the combustion worse, resulting in the increase of HC, soot and CO emissions. NOx emissions decrease with the advance of the injection time.

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Effect of Injection Timing on PPCI and MPCI Mode Fueled With Straight-Run Naphtha

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4025722 ◽

2013 ◽

Vol 136 (3) ◽

Cited By ~ 3

Author(s):

Hongqiang Yang ◽

Shijin Shuai ◽

Zhi Wang ◽

Jianxin Wang

Keyword(s):

Diesel Fuel ◽

Single Injection ◽

Operating Conditions ◽

Premixed Combustion ◽

Spray Combustion ◽

Injection Timing ◽

Soot Emission ◽

Compression Ignition ◽

Injection Strategy ◽

Injection Strategies

Partially premixed compression ignition (PPCI) and multiple premixed compression ignition (MPCI) mode of straight-run naphtha have been investigated under different injection strategies. The MPCI mode is realized by the multiple premixed combustion processes in a sequence of “spray-combustion-spray-combustion” around the compression top dead center. The spray and combustion events are preferred to be completely separated, without any overlap in the temporal sequence in order to ensure the multiple-stage premixed compression ignition. The PPCI mode is well known as the “spray-spray-combustion” sequence, with the start of combustion separated from the end of injection. Straight-run naphtha with a research octane number (RON) of 58.8 is tested in a single cylinder compression ignition engine whose compression ratio is 16.7 and displacement is 0.5 l. Double and triple injection strategies are investigated as the last injection timing sweeping at 1.0 MPa IMEP and 1800 rpm conditions. The MPCI mode is achieved using the double injection strategy, but its soot emission is higher than the PPCI mode under triple injection strategy. This is mainly because of the lower RON of the straight-run naphtha and the ignition delay is too short to form an ideally premixed combustion process after the second injection of straight-run naphtha. Diesel fuel is also tested under the same operating conditions, except for employing a single injection strategy. The naphtha PPCI and MPCI mode both have lower fuel consumption and soot emission than diesel fuel single injection mode, but the THC emissions are both higher than that of diesel fuel.

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Post Injection Strategy for the Reduction of the Peak Pressure Rise Rate of Neat N-Butanol Combustion

Volume 1: Large Bore Engines; Fuels; Advanced Combustion ◽

10.1115/icef2015-1066 ◽

2015 ◽

Author(s):

Marko Jeftić ◽

Ming Zheng

Keyword(s):

Peak Pressure ◽

Pressure Rise ◽

Injection Timing ◽

Post Injection ◽

Compression Ignition ◽

Cylinder Pressure ◽

Compression Ignition Engine ◽

Pressure Rise Rate ◽

Injection Duration ◽

Rise Rate

Enhanced premixed combustion of neat butanol in a compression ignition engine can have challenges with regards to the peak pressure rise rate and the peak in-cylinder pressure. It was proposed to utilize a butanol post injection to reduce the peak pressure rise rate and the peak in-cylinder pressure while maintaining a constant engine load. Post injection timing and duration sweeps were carried out with neat n-butanol in a compression ignition engine. The post injection timing sweep results indicated that the use of an early butanol post injection reduced the peak pressure rise rate and the peak in-cylinder pressure and it was observed that there was an optimal post injection timing range for the maximum reduction of these parameters. The results also showed that an early post injection of butanol increased the nitrogen oxide emissions and an FTIR analysis revealed that late post injections increased the emissions of unburned butanol. The post injection duration sweep indicated that the peak pressure rise rate was significantly reduced by increasing the post injection duration at constant load conditions. There was also a reduction in the peak in-cylinder pressure. Measurements with a hydrogen mass spectrometer showed that there was an increased presence of hydrogen in the exhaust gas when the post injection duration was increased but the total yield of hydrogen was relatively low. It was observed that the coefficient of variation for the indicated mean effective pressure was significantly increased and that the indicated thermal efficiency was reduced when the post injection duration was increased. The results also showed that there were increased nitrogen oxide, carbon monoxide, and total hydrocarbon emissions for larger post injections. Although the use of a post injection resulted in emission and thermal efficiency penalties at medium load conditions, the results demonstrated that the post injection strategy successfully reduced the peak pressure rise rate and this characteristic can be potentially useful for higher load applications where the peak pressure rise rate is of greater concern.

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A Review of Early Injection Strategy in Premixed Combustion Engines

Applied Sciences ◽

10.3390/app9183737 ◽

2019 ◽

Vol 9 (18) ◽

pp. 3737 ◽

Cited By ~ 3

Author(s):

Xingyu Liang ◽

Zhiwei Zheng ◽

Hongsheng Zhang ◽

Yuesen Wang ◽

Hanzhengnan Yu

Keyword(s):

Diesel Engines ◽

Alternative Fuels ◽

Exhaust Emissions ◽

Injection Timing ◽

Compression Ignition ◽

Injection Strategy ◽

Advantages And Disadvantages ◽

Injection Parameters ◽

Performance And Emissions ◽

Early Injection

Due to the increasing awareness of environmental protection, limitations on exhaust emissions of diesel engines have become increasingly stringent. This challenges diesel engine manufacturers to find a new balance between engine performance and emissions. Advanced combustion modes for diesel engines, such as homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI), which can simultaneously reduce exhaust emissions and substantially improve thermal efficiency, have drawn increasing attention. In order to allow enough time to prepare the homogeneous mixture, the early injection strategy has been utilized widely in HCCI and PCCI diesel engines. This paper is aimed at providing a comprehensive review of the effects of early injection parameters on the performance and emissions of HCCI and PCCI engines fueled by both diesel and alternative fuels. Various early injection parameters, including injection pressure, injection timing, and injection angle, are discussed. In addition, the effect of the blending ratio of alternative fuels is also summarized. Every change in parameters has its own advantages and disadvantages, which are explained in detail in order to help researchers choose the best early injection parameters for HCCI and PCCI engines.

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Fuel Stratification and Partially Premixed Combustion With Neat n-Butanol in a Compression Ignition Engine

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4040517 ◽

2018 ◽

Vol 140 (12) ◽

Cited By ~ 3

Author(s):

Shouvik Dev ◽

Tongyang Gao ◽

Xiao Yu ◽

Mark Ives ◽

Ming Zheng

Keyword(s):

Fuel Injection ◽

Direct Injection ◽

Premixed Combustion ◽

Injection Timing ◽

Compression Ignition ◽

Compression Ignition Engine ◽

Fuel Stratification ◽

Partially Premixed Combustion ◽

Partially Premixed ◽

Ci Engines

Homogeneous charge compression ignition (HCCI) has been considered as an ideal combustion mode for compression ignition (CI) engines due to its superb thermal efficiency and low emissions of nitrogen oxides (NOx) and particulate matter. However, a challenge that limits practical applications of HCCI is the lack of control over the combustion rate. Fuel stratification and partially premixed combustion (PPC) have considerably improved the control over the heat release profile with modulations of the ratio between premixed fuel and directly injected fuel, as well as injection timing for ignition initiation. It leverages the advantages of both conventional direct injection compression ignition and HCCI. In this study, neat n-butanol is employed to generate the fuel stratification and PPC in a single cylinder CI engine. A fuel such as n-butanol can provide additional benefits of even lower emissions and can potentially lead to a reduced carbon footprint and improved energy security if produced appropriately from biomass sources. Intake port fuel injection (PFI) of neat n-butanol is used for the delivery of the premixed fuel, while the direct injection (DI) of neat n-butanol is applied to generate the fuel stratification. Effects of PFI-DI fuel ratio, DI timing, and intake pressure on the combustion are studied in detail. Different conditions are identified at which clean and efficient combustion can be achieved at a baseline load of 6 bar IMEP. An extended load of 14 bar IMEP is demonstrated using stratified combustion with combustion phasing control.

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A Study of Injection Strategy to Achieve High Load Points for Gasoline Compression Ignition (GCI) Operation

Volume 1: Large Bore Engines; Fuels; Advanced Combustion ◽

10.1115/icef2017-3625 ◽

2017 ◽

Cited By ~ 4

Author(s):

Khanh Cung ◽

Stephen Ciatti

Keyword(s):

High Efficiency ◽

Cetane Number ◽

Load Condition ◽

Low Noise ◽

High Load ◽

Premixed Combustion ◽

Injection Timing ◽

Compression Ignition ◽

Injection Strategy ◽

Engine Load

Many studies have shown that gasoline compression ignition (GCI) can replace conventional diesel combustion (CDC) by achieving high efficiency and low smoke and toxic gaseous emissions simultaneously. This is due to the low cetane number of gasoline that results in long ignition delay, allowing very advanced injection timing. This gives even longer time for fuel-air mixing, thus resulting in locally lean combustion that produces low particulate matter (PM). However, GCI operation faces challenges at high engine load condition. At high load conditions, large amounts of fuel injected early for premixed combustion can lead to high combustion noise from premixed combustion. Meanwhile, more fuel late injected late leads to poor mixing, hence higher smoke. Multiple injections can offer the flexibility in controlling the in-cylinder fuel stratification level. In this study, moderate to high engine loads of 8 to 14 bar BMEP were accomplished by utilizing an optimal multiple injection scheme. Injection timing of pilot, main, and post injections was investigated individually for its effect on the emission and engine performance. A moderate level of exhaust gas recirculating (EGR) was used to achieve low temperature combustion (LTC) condition. While higher EGR reduced NOx significantly due to lower combustion temperature, it affected the maximum boost that could be acquired by the turbocharger due to the reduction in exhaust enthalpy. During the engine load/speed sweep, calculations of combustion, thermodynamics, gas exchange, and mechanical efficiencies were analyzed to identify factor that needs to be improved for GCI operation. This study also demonstrates the importance of injection strategy including high injection pressure to attain high load points with low smoke and low noise.

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Effect of Premixed Fuel Preparation for Partially Premixed Combustion With a Low Octane Gasoline on a Light-Duty Multicylinder Compression Ignition Engine

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4030281 ◽

2015 ◽

Vol 137 (11) ◽

Cited By ~ 15

Author(s):

Adam B. Dempsey ◽

Scott Curran ◽

Robert Wagner ◽

William Cannella

Keyword(s):

High Pressure ◽

Thermal Efficiency ◽

Fuel Injection ◽

Premixed Combustion ◽

Injection System ◽

Injection Timing ◽

Pilot Injection ◽

Compression Ignition ◽

Partially Premixed Combustion ◽

Injection Strategies

Gasoline compression ignition (GCI) concepts with the majority of the fuel being introduced early in the cycle are known as partially premixed combustion (PPC). Previous research on single- and multicylinder engines has shown that PPC has the potential for high thermal efficiency with low NOx and soot emissions. A variety of fuel injection strategies have been proposed in the literature. These injection strategies aim to create a partially stratified charge to simultaneously reduce NOx and soot emissions while maintaining some level of control over the combustion process through the fuel delivery system. The impact of the direct injection (DI) strategy to create a premixed charge of fuel and air has not previously been explored, and its impact on engine efficiency and emissions is not well understood. This paper explores the effect of sweeping the direct injected pilot timing from −91 deg to −324 deg ATDC, which is just after the exhaust valve closes (EVCs) for the engine used in this study. During the sweep, the pilot injection consistently contained 65% of the total fuel (based on command duration ratio), and the main injection timing was adjusted slightly to maintain combustion phasing near top dead center. A modern four cylinder, 1.9 l diesel engine with a variable geometry turbocharger (VGT), high pressure common rail injection system, wide included angle injectors, and variable swirl actuations was used in this study. The pistons were modified to an open bowl configuration suitable for highly premixed combustion modes. The stock diesel injection system was unmodified, and the gasoline fuel was doped with a lubricity additive to protect the high pressure fuel pump and the injectors. The study was conducted at a fixed speed/load condition of 2000 rpm and 4.0 bar brake mean effective pressure (BMEP). The pilot injection timing sweep was conducted at different intake manifold pressures, swirl levels, and fuel injection pressures. The gasoline used in this study has relatively high fuel reactivity with a research octane number of 68. The results of this experimental campaign indicate that the highest brake thermal efficiency (BTE) and lowest emissions are achieved simultaneously with the earliest pilot injection timings (i.e., during the intake stroke).

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Effects of Injector Nozzle Inclusion Angle on Extending the Lower Load Limit of Gasoline Compression Ignition Using 87 AKI Gasoline

Volume 1: Large Bore Engines; Fuels; Advanced Combustion; Emissions Control Systems ◽

10.1115/icef2014-5632 ◽

2014 ◽

Cited By ~ 2

Author(s):

Christopher P. Kolodziej ◽

Stephen A. Ciatti

Keyword(s):

Injection Pressure ◽

Premixed Combustion ◽

Injection Timing ◽

Compression Ignition ◽

Effective Pressure ◽

Advantages And Disadvantages ◽

Injector Nozzle ◽

Brake Mean Effective Pressure ◽

Low Load ◽

Ignition Propensity

Gasoline Compression Ignition (GCI) is a promising single-fuel advanced combustion concept for increased efficiency and reduced emissions in comparison with current conventional combustion modes. Gasoline fuels are advantageous in premixed combustion concepts because of their increased volatility and reduced reactivity compared to diesel. These qualities help reduce emissions of particulate matter (PM) and oxides of nitrogen (NOx), while making combustion phasing (and therefore combustion noise reduction) easier to manage. One of the challenges of using a gasoline with an anti-knock index (AKI) of 87 in a premixed combustion concept is being able to achieve stable low load operation. (Note that AKI is equivalent to (RON + MON)/2.) With such small injection quantities of a relatively more volatile and less reactive fuel than diesel, the injection timing of minimum load fueling needs to be early enough to allow the auto-ignition chemistry enough time, but late enough to keep the fuel from over-mixing and losing ignition propensity. The objective of this study was to investigate the advantages and disadvantages of reducing the injector nozzles’ inclusion angle from 148° to 120° on the combustion and emissions performance of GCI at 850 RPM and low load. To assess these effects, minimum fueling injection timing sweeps were performed with a 3% coefficient of variance of indicated mean effective pressure with each injector nozzle angle at 500 and 250 bar injection pressure. The results from these experiments revealed that both reduced injector nozzle angle and reduced injection pressure increased ignition propensity and allowed for reduced fueling and stable low load extension to 1 bar brake mean effective pressure using 87 AKI gasoline without any external boosting or heating. Combustion characteristics (such as noise) and emissions are discussed.

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