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Technical Paper

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

2019-09-09
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 spark ignition (PCSI) 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, a unique pre-chamber geometry was tested in a single-cylinder heavy-duty engine at low load lean conditions. The geometry features a narrow throat, which was designed to be packaged inside a commercial diesel injector pocket. The pre-chamber was fueled with methane while the main chamber was supplied with an ethanol/air mixture.
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

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

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

Double Compression Expansion Engine: A Parametric Study on a High-Efficiency Engine Concept

2018-04-03
2018-01-0890
The Double compression expansion engine (DCEE) concept has exhibited a potential for achieving high brake thermal efficiencies (BTE). The effect of different engine components on system efficiency was evaluated in this work using GT Power simulations. A parametric study on piston insulation, convection heat transfer multiplier, expander head insulation, insulation of connecting pipes, ports and tanks, and the expander intake valve lift profiles was conducted to understand the critical parameters that affected engine efficiency. The simulations were constrained to a constant peak cylinder pressure of 300 bar, and a fixed combustion phasing. The results from this study would be useful in making technology choices that will help realise the potential of this engine concept.
Technical Paper

Comparison of Gasoline and Primary Reference Fuel in the Transition from HCCI to PPC

2017-10-08
2017-01-2262
Our previous research investigated the sensitivity of combustion phasing to intake temperature and injection timing during the transition from homogeneous charge compression ignition (HCCI) to partially premixed combustion (PPC) fuelled with generic gasoline. The results directed particular attention to the relationship between intake temperature and combustion phasing which reflected the changing of stratification level with the injection timing. To confirm its applicability with the use of different fuels, and to investigate the effect of fuel properties on stratification formation, primary reference fuels (PRF) were tested using the same method: a start of injection sweep from -180° to -20° after top dead center with constant combustion phasing by tuning the intake temperature. The present results are further developed compared with those of our previous work, which were based on generic gasoline.
Technical Paper

Fuel Effect on Combustion Stratification in Partially Premixed Combustion

2017-09-04
2017-24-0089
The literature study on PPC in optical engine reveals investigations on OH chemiluminescence and combustion stratification. So far, mostly PRF fuel is studied and it is worthwhile to examine the effect of fuel properties on PPC. Therefore, in this work, fuel having different octane rating and physical properties are selected and PPC is studied in an optical engine. The fuels considered in this study are diesel, heavy naphtha, light naphtha and their corresponding surrogates such as heptane, PRF50 and PRF65 respectively. Without EGR (Intake O2 = 21%), these fuels are tested at an engine speed of 1200 rpm, fuel injection pressure of 800 bar and pressure at TDC = 35 bar. SOI is changed from late to early fuel injection timings to study PPC and the shift in combustion regime from CI to PPC is explored for all fuels. An increased understanding on the effect of fuel octane number, physical properties and chemical composition on combustion and emission formation is obtained.
Technical Paper

Optimum Heat Release Rates for a Double Compression Expansion (DCEE) Engine

2017-03-28
2017-01-0636
The concept of double compression, and double expansion engine (DCEE) for improving the efficiency of piston reciprocating engines was introduced in SAE Paper 2015-01-1260. This engine configuration has separate high, and low pressure units thereby effectively reducing friction losses for high effective compression ratios. The presence of an additional expander stage also theoretically allows an extra degree of freedom to manipulate the combustion heat release rate so as to achieve better optimum between heat transfer, and friction losses. This paper presents a 1-D modeling study of the engine concept in GT-Power for assessing the sensitivity of engine losses to heat release rate. The simulations were constrained by limiting the maximum pressure to 300 bar.
Technical Paper

Influence of Injection Timing on Exhaust Particulate Matter Emissions of Gasoline in HCCI and PPC

2016-10-17
2016-01-2300
In order to reduce nitrogen oxides (NOx) and soot emissions while maintaining high thermal efficiency, more advanced combustion concepts have been developed over the years, such as Homogeneous Charge Compression Ignition (HCCI) and Partially Premixed Combustion (PPC), as possible combustion processes in commercial engines. Compared to HCCI, PPC has advantages of lower unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions; however, due to increased fuel stratifications, soot emissions can be a challenge when adding Exhaust-Gas Recirculation (EGR) gas. The current work presents particle size distribution measurements performed from HCCI-like combustion with very early (120 CAD BTDC) to PPC combustion with late injection timing (11 CAD BTDC) at two intake oxygen rates, 21% and 15% respectively. Particle size distributions were measured using a differential mobility spectrometer DMS500.
Technical Paper

Transition from HCCI to PPC: the Sensitivity of Combustion Phasing to the Intake Temperature and the Injection Timing with and without EGR

2016-04-05
2016-01-0767
An experiment was conducted to investigate the effect of charge stratification on the combustion phasing in a single cylinder, heavy duty (HD) compression ignition (CI) engine. To do this the start of injection (SOI) was changed from -180° after top dead centre (ATDC) to near top dead centre (TDC) during which CA50 (the crank angle at which 50% of the fuel energy is released) was kept constant by changing the intake temperature. At each SOI, the response of CA50 to a slight increase or decrease of either intake temperature or SOI were also investigated. Afterwards, the experiment was repeated with a different intake oxygen concentration. The results show that, for the whole SOI period, the required intake temperature to keep constant CA50 has a “spoon” shape with the handle on the -180° side.
Technical Paper

An Experimental Investigation of a Multi-Cylinder Engine with Gasoline-Like Fuel towards a High Engine Efficiency

2016-04-05
2016-01-0763
Partially Premixed Combustion (PPC) is a promising combustion concept with high thermodynamic efficiency and low emission level, and also with minimal modification of standard engine hardware. To use PPC in a production oriented engine, the optimal intake charge conditions for PPC should be included in the analysis. The experiments in this paper investigated and confirmed that the optimal intake conditions of net indicated efficiency for PPC are EGR between 50% and 55% as possible and the lambda close to 1.4. Heat-transfer energy and exhaust gas waste-energy contribute to the majority of the energy loss in the engine. The low EGR region has high heat-transfer and low exhaust gas enthalpy-waste, while the high EGR region has low heat-transfer and high exhaust gas waste-enthalpy. The optimal EGR condition is around 50% where the smallest energy loss is found as a trade-off between heat transfer and exhaust-gas enthalpy-waste.
Technical Paper

High-Speed Particle Image Velocimetry Measurement of Partially Premixed Combustion (PPC) in a Light Duty Engine for Different Injection Strategies

2015-09-06
2015-24-2454
It has been proven that partially premixed combustion (PPC) has the capability of high combustion efficiency with low soot and NOx emissions, which meet the requirements of increasingly restricted emission regulations. In order to obtain more homogenous combustion and longer ignition delay in PPC, different fuel injection strategies were employed which could affect the fuel air mixing and control the combustion. In the present work, a light duty optical diesel engine was used to conduct high speed particle image velocimetry (PIV) for single, double and triple injections with different timings. A quartz piston and a cylinder liner were installed in the Bowditch configuration to enable optical access. The geometry of the quartz piston crown is based on the standard diesel combustion chamber design for this commercial passenger car engine, including a re-entrant bowl shape.
Technical Paper

Analysis of Soot Particles in the Cylinder of a Heavy Duty Diesel Engine with High EGR

2015-09-06
2015-24-2448
When applying high amount of EGR (exhaust gas recirculation) in Partially Premixed Combustion (PPC) using diesel fuel, an increase in soot emission is observed as a penalty. To better understand how EGR affects soot particles in the cylinder, a fast gas sampling technique was used to draw gas samples directly out of the combustion chamber in a Scania D13 heavy duty diesel engine. The samples were characterized on-line using a scanning mobility particle sizer for soot size distributions and an aethalometer for black carbon (soot) mass concentrations. Three EGR rates, 0%, 56% and 64% were applied in the study. It was found that EGR reduces both the soot formation rate and the soot oxidation rate, due to lower flame temperature and a lower availability of oxidizing agents. With higher EGR rates, the peak soot mass concentration decreased. However, the oxidation rate was reduced even more.
Technical Paper

Transition from HCCI to PPC Combustion by Means of Start of Injection

2015-09-01
2015-01-1790
Partially premixed combustion (PPC) is a promising way to achieve high efficiency and low engine-out emissions simultaneously in a heavy-duty engine. Compared to Homogeneous Charge Compression Ignition (HCCI), it can be controlled by injection events and much lower HC and CO emissions can be achieved. This work focuses on the transition from HCCI to PPC and combustion and emissions characteristics during the process are investigated. Injection strategies, EGR and boost pressure were the main parameters used to present the corresponding effect during the transition.
Technical Paper

Sensitivity Analysis of Partially Premixed Combustion (PPC) for Control Purposes

2015-04-14
2015-01-0884
Partially Premixed Combustion (PPC) is a promising advanced combustion mode for future engines. In order to investigate the sensitivity of PPC to exhaust gas recirculation (EGR) rate, intake gas temperature, intake gas pressure, and injection timing, these parameters were swept individually at three different loads in a single cylinder diesel engine with gasoline-like fuel. A factor of sensitivity was defined to indicate the combustion's controllability and sensitivity to inlet gas parameters and injection timings. Through analysis of experimental results, a control window of inlet gas parameters and injection timings is obtained at different loads in PPC mode from 5 bar to 10 bar IMEPg load at 1200 rpm. To further study the PPC controllability with injection timing, main injection timing was adjusted to sustain steady combustion phasing subject to perturbation of inlet gas state.
Journal Article

Combustion Stratification with Partially Premixed Combustion, PPC, using NVO and Split Injection in a LD - Diesel Engine

2014-10-13
2014-01-2677
Partially Premixed Combustion (PPC) is used to meet the increasing demands of emission legislation and to improve fuel efficiency. PPC with gasoline fuels have the advantage of a longer premixed duration of fuel/air mixture which prevents soot formation at higher loads. The objective of this paper is to investigate the degree of stratification for low load (towards idle) engine conditions using different injection strategies and negative valve overlap (NVO). The question is, how homogenous or stratified is the partially premixed combustion (PPC) for a given setting of NVO and fuel injection strategy. In this work PRF 55 has been used as PPC fuel. The experimental engine is a light duty (LD) diesel engine that has been modified to single cylinder operation to provide optical access into the combustion chamber, equipped with a fully variable valve train system. Hot residual gases were trapped by using NVO to dilute the cylinder mixture.
Journal Article

Study of the Early Flame Development in a Spark-Ignited Lean Burn Four-Stroke Large Bore Gas Engine by Fuel Tracer PLIF

2014-04-01
2014-01-1330
In this work the pre- to main chamber ignition process is studied in a Wärtsilä 34SG spark-ignited lean burn four-stroke large bore optical engine (bore 340 mm) operating on natural gas. Unburnt and burnt gas regions in planar cross-sections of the combustion chamber are identified by means of planar laser induced fluorescence (PLIF) from acetone seeded to the fuel. The emerging jets from the pre-chamber, the ignition process and early flame propagation are studied. Measurements reveal the presence of a significant temporal delay between the occurrence of a pressure difference across the pre-chamber holes and the appearance of hot burnt/burning gases at the nozzle exit. Variations in the delay affect the combustion timing and duration. The combustion rate in the pre-chamber does not influence the jet propagation speed, although it still has an effect on the overall combustion duration.
Technical Paper

A Study on In-Cycle Control of NOx Using Injection Strategy with a Fast Cylinder Pressure Based Emission Model as Feedback

2013-10-14
2013-01-2603
The emission control in heavy-duty vehicles today is based on predefined injection strategies and after-treatment systems such as SCR (selective catalytic reduction) and DPF (diesel particulate filter). State-of-the-art engine control is presently based on cycle-to-cycle resolution. The introduction of the crank angle resolved pressure measurement, from a piezo-based pressure sensor, enables the possibility to control the fuel injection based on combustion feedback while the combustion is occurring. In this paper a study is presented on the possibility to control NOx (nitrogen oxides) formation with a crank angle resolved NOx estimator as feedback. The estimator and the injection control are implemented on an FPGA (Field-Programmable Gate Array) to manage the inherent time constraints. The FPGA is integrated with the rest of the engine control system for injection control and measurement.
Technical Paper

Loss Analysis of a HD-PPC Engine with Two-Stage Turbocharging Operating in the European Stationary Cycle

2013-10-14
2013-01-2700
Partially Premixed Combustion (PPC) has demonstrated substantially higher efficiency compared to conventional diesel combustion (CDC) and gasoline engines (SI). By combining experiments and modeling the presented work investigates the underlying reasons for the improved efficiency, and quantifies the loss terms. The results indicate that it is possible to operate a HD-PPC engine with a production two-stage boost system over the European Stationary Cycle while likely meeting Euro VI and US10 emissions with a peak brake efficiency above 48%. A majority of the ESC can be operated with brake efficiency above 44%. The loss analysis reveals that low in-cylinder heat transfer losses are the most important reason for the high efficiencies of PPC. In-cylinder heat losses are basically halved in PPC compared to CDC, as a consequence of substantially reduced combustion temperature gradients, especially close to the combustion chamber walls.
Technical Paper

Effects of EGR and Intake Pressure on PPC of Conventional Diesel, Gasoline and Ethanol in a Heavy Duty Diesel Engine

2013-10-14
2013-01-2702
Partially Premixed Combustion (PPC) has the potential of simultaneously providing high engine efficiency and low emissions. Previous research has shown that with proper combination of Exhaust-Gas Recirculation (EGR) and Air-Fuel equivalence ratio, it is possible to reduce engine-out emissions while still keeping the engine efficiency high. In this paper, the effect of changes in intake pressure (boost) and EGR fraction on PPC engine performance (e.g. ignition delay, burn duration, maximum pressure rise rate) and emissions (carbon monoxide (CO), unburned hydrocarbon (UHC), soot and NOX) was investigated in a single-cylinder, heavy-duty diesel engine. Swedish diesel fuel (MK1), RON 69 gasoline fuel and 99.5 vol% ethanol were tested. Fixed fueling rate and single injection strategy were employed.
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