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Technical Paper

Optimization and Evaluation of a Low Temperature Waste Heat Recovery System for a Heavy Duty Engine over a Transient Cycle

2020-09-15
2020-01-2033
Powertrain efficiency is a critical factor in lowering fuel consumption and reducing the emission of greenhouse gases for an internal combustion engine. One method to increase the powertrain efficiency is to recover some of the wasted heat from the engine using a waste heat recovery system e.g. an organic Rankine cycle. Most waste heat recovery systems in use today for combustion engines use the waste heat from the exhaust gases due to the high temperatures and hence, high energy quality. However, the coolant represents a major source of waste heat in the engine that is mostly overlooked due to its lower temperature. This paper studies the potential of using elevated coolant temperatures in internal combustion engines to improve the viability of low temperature waste heat recovery.
Technical Paper

Numerical Optimization of Compression Ratio for a PPC Engine running on Methanol

2019-12-19
2019-01-2168
Partially premixed combustion (PPC) has shown to produce high gross indicated efficiencies while yielding lower pollutant emissions, such as oxides of nitrogen and soot, than conventional diesel combustion. Gasoline fuels with a research octane number (RON) of 60-70 have been proposed as optimal for PPC as they balance the trade-off between ensuring good combustion stability at low engine loads and avoiding excessive peak pressure rise rates at high loads. However, measures have to be taken when optimizing the engine operating parameters to avoid soot emissions. In contrast, methanol has a much lower propensity for soot formation. However, due to a higher RON of methanol the required intake temperature is higher for the same engine compression ratio to ensure auto-ignition at an appropriate timing. Increasing the compression ratio allows a lower intake temperature and improves combustion stability as well as engine brake efficiency.
Technical Paper

Literature Review on Dual-Fuel Combustion Modelling

2019-09-09
2019-24-0120
In the search for low greenhouse gas propulsion, the dual fuel engine provides a solution to use low carbon fuel at diesel-like high efficiency. Also a lower emission of NOx and particles can be achieved by replacing a substantial part of the diesel fuel by for example natural gas. Limitations can be found in excessively high heat release rate (combustion-knock), and high methane emissions. These limitations are strongly influenced by operating parameters and properties of the used (bio)-gas. To find the dominant relations between fuel properties, operating parameters and the heat release rate and methane emissions, a combustion model is beneficial. Such a model can be used for optimizing the process, or can even be used in real time control. As precursor for such a model, the current state of art of dual fuel combustion modelling is investigated in this work. The focus is on high speed dual fuel engines for heavy duty and marine applications, with a varying gas/diesel ratio.
Technical Paper

A Coupled Tabulated Kinetics and Flame Propagation Model for the Simulation of Fumigated Medium Speed Dual-Fuel Engines

2019-09-09
2019-24-0098
The present work describes the numerical modeling of medium-speed marine engines, operating in a fumigated dual-fuel mode, i.e. with the second fuel injected in the ports. This engine technology allows reducing engine-out emissions while maintaining the engine efficiency and can be fairly easily retrofitted from current diesel engines. The main premixed fuel that is added can be a low-carbon one and can additionally be of a renewable nature, thereby reducing or even completely removing the global warming impact. To fully optimize the operational parameters of such a large marine engine, computational fluid dynamics can be very helpful. Accurately describing the combustion process in such an engine is key, as the prediction of the heat release and the pollutant formation is crucial. Auto-ignition of the diesel fuel needs to be captured, followed by the combustion and flame propagation of the premixed fuel.
Journal Article

Influence of Injection Strategies on Engine Efficiency for a Methanol PPC Engine

2019-09-09
2019-24-0116
Partially premixed combustion (PPC) is one of several advanced combustion concepts for the conventional diesel engine. PPC uses a separation between end of fuel injection and start of combustion, also called ignition dwell, to increase the mixing of fuel and oxidizer. This has been shown to be beneficial for simultaneously reducing harmful emissions and fuel consumption. The ignition dwell can be increased by means of exhaust gas recirculation or lower intake temperature. However, the most effective means is to use a fuel with high research octane number (RON). Methanol has a RON of 109 and a recent study found that methanol can be used effectively in PPC mode, with multiple injections, to yield high brake efficiency. However, the early start of injection (SOI) timings in this study were noted as a potential issue due to increased combustion sensitivity. Therefore, the present study attempts to quantify the changes in engine performance for different injection strategies.
Technical Paper

Combustion Characterization of Methanol in a Lean Burn Direct Injection Spark Ignition (DISI) Engine

2019-04-02
2019-01-0566
Lean operation is a promising approach to increase the engine efficiency. One of the main challenges for lean-burn technology is the combustion instability. Using a high laminar burning velocity fuel such as methanol might solve that problem. The potential of lean-burn limit extension with methanol was investigated through a comparison with conventional gasoline. In this work, a direct injection turbocharged SI engine was operated at wide open throttle (WOT), with the load controlled by a lean-burn strategy. The amount of fuel was decreased (or lambda increased) until the combustion became unstable. For methanol, the lambda limit was about 1.5, higher than the lambda limit for gasoline which was only about 1.2. The brake thermal efficiency for methanol increased as lambda increased and reached its peak at ~41% in a lambda range of 1.2-1.4. Then, the efficiency decreased as lambda increased.
Technical Paper

Cylinder to Cylinder Variation Related to Gas Injection Timing on a Dual-Fuel Engine

2019-04-02
2019-01-1162
The natural gas/diesel dual-fuel engine is an interesting technique to reduce greenhouse gas emission. A limitation of this concept is the emission of un-combusted methane. In this study we analyzed the influence of PFI gas-injection timing on cylinder to cylinder gas-distribution, and the resulting methane emissions. This was done on a 6 cylinder HD engine test bench and in a GT-power simulation of the same engine. The main variable in all tests was the timing of the intake port gas injection, placed either before, after, or during the intake stroke. It showed that injecting outside of the intake window resulted in significant variation of the amount of trapped gaseous fuel over the 6 cylinders, having a strong impact on methane emissions. Injecting outside of the intake stroke results in gas awaiting in the intake port. Both testing and simulation made clear that as a result of this, cylinder 1 leans out and cylinder 6 enriches.
Technical Paper

The Relevance of Different Fuel Indices to Describe Autoignition Behaviour of Gasoline in Light Duty DICI Engine under PPC Mode

2019-04-02
2019-01-1147
Partially premixed combustion (PPC) with gasoline fuels is a new promising combustion concept for future internal combustion engines. However, many researchers have argued the capabilities of research octane number (RON) and Motor Octane Number (MON) to describe the autoignition behaviour of gasoline fuels in advanced combustion concepts like PPC. The objective of this study is to propose a new method, called PPC number, to characterize the auto ignition quality of gasoline fuels in a light-duty direct injected compression ignition engine under PPC conditions. The experimental investigations were performed on a 4-cylinder Volvo D4 2 litre engine. The ignition delay which was defined as the crank angle degrees between the start of injection (SOI) and start of combustion (SOC) was used to represent the auto ignition quality of a fuel.
Technical Paper

Simulation Based Investigation of Achieving Low Temperature Combustion with Methanol in a Direct Injected Compression Ignition Engine

2019-04-02
2019-01-1152
Low temperature combustion concepts used in compression ignition engines have shown to be able to produce simultaneous reduction of oxides of nitrogen and soot as well as generating higher gross indicated efficiencies compared to conventional diesel combustion. This is achieved by a combination of premixing, dilution and optimization of combustion phasing. Low temperature combustion can be complemented by moving away from fossil fuels in order to reduce the net output of CO2 emissions. Alternative fuels are preferably liquid and of sufficient energy density. As such methanol is proposed as a viable option. This paper reports the results from a simulation based investigation on a heavy-duty multi-cylinder direct injection compression ignition engine with standard compression ratio. The engine was simulated using two different fuels: methanol and gasoline with an octane number of 70.
Technical Paper

A Heat Transfer Model for Low Temperature Combustion Engines

2018-09-10
2018-01-1662
Low Temperature Combustion is a technology that enables achieving both a higher efficiency and simultaneously lower emissions of NOx and particulate matter. It is a noun for combustion regimes that operate with a lean air-fuel mixture and where the combustion occurs at a low temperature, such as Homogeneous Charge Compression Ignition and Partially Premixed Combustion. In this work a new model is proposed to predict the instantaneous heat flux in engines with Low Temperature Combustion. In-cylinder heat flux measurements were used to construct this model. The new model addresses two shortcomings of the existing heat transfer models already present during motored operation: the phasing of the instantaneous heat flux and the overprediction of the heat flux during the expansion phase. This was achieved by implementing the in-cylinder turbulence in the heat transfer model. The heat transfer during the combustion was taken into account by using the turbulence generated in the burned zone.
Technical Paper

Downsizing Potential of Methanol Fueled DISI Engine with Variable Valve Timing and Boost Control

2018-04-03
2018-01-0918
Methanol is gaining traction in some regions, e.g. for road transportation in China and for marine transportation in Europe. In this research, the possibility for achieving higher power output and higher efficiency with methanol, compared to gasoline, is investigated and the influence of several engine settings, such as valve timing and intake boost control, is studied. At wide open throttle (WOT), engine speed of 1650 rpm, the brake mean effective pressure (BMEP) of the methanol-fueled engine is higher than on gasoline, by around 1.8 bar. The maximum BMEP is further increased when positive valve overlap and higher intake boost pressure are applied. Thanks to a lower residual gas fraction, and a richer in-cylinder mixture with positive valve overlap period, the engine BMEP improves by a further 2.6 bar. Because of higher volumetric efficiency with a boosted intake air, the engine BMEP enhances with 4.7 bar.
Technical Paper

Studying the Effect of the Flame Passage on the Convective Heat Transfer in a S.I. Engine

2017-03-28
2017-01-0515
Engine optimization requires a good understanding of the in-cylinder heat transfer since it affects the power output, engine efficiency and emissions of the engine. However little is known about the convective heat transfer inside the combustion chamber due to its complexity. To aid the understanding of the heat transfer phenomena in a Spark Ignition (SI) engine, accurate measurements of the local instantaneous heat flux are wanted. An improved understanding will lead to better heat transfer modelling, which will improve the accuracy of current simulation software. In this research, prototype thin film gauge (TFG) heat flux sensors are used to capture the transient in-cylinder heat flux within a Cooperative Fuel Research (CFR) engine. A two-zone temperature model is linked with the heat flux data. This allows the distinction between the convection coefficient in the unburned and burned zone.
Technical Paper

Development of Laminar Burning Velocity Correlation for the Simulation of Methanol Fueled SI Engines Operated with Onboard Fuel Reformer

2017-03-28
2017-01-0539
Methanol fueled spark ignition (SI) engines have the potential for very high efficiency using an advanced heat recovery system for fuel reforming. In order to allow simulation of such an engine system, several sub-models are needed. This paper reports the development of two laminar burning velocity correlations, corresponding to two reforming concepts, one in which the reformer uses water from an extra tank to produce hydrogen rich gas (syngas) and another that employs the water vapor in the exhaust gas recirculation (EGR) stream to produce reformed-EGR (R-EGR). This work uses a one-dimensional (1D) flame simulation tool with a comprehensive chemical kinetic mechanism to predict the laminar burning velocities of methanol/syngas blends and correlate it. The syngas is a mixture of H2/CO/CO2 with a CO selectivity of 6.5% to simulate the methanol steam reforming products over a Cu-Mn/Al catalyst.
Technical Paper

Experimental Investigation and Modelling of the In-Cylinder Heat Transfer during Ringing Combustion in an HCCI Engine

2017-03-28
2017-01-0732
Homogeneous Charge Compression Ignition (HCCI) engines can achieve both a high thermal efficiency and near-zero emissions of NOx and soot. However, their maximum attainable load is limited by the occurrence of a ringing combustion. At high loads, the fast combustion rate gives rise to pressure oscillations in the combustion chamber accompanied by a ringing or knocking sound. In this work, it is investigated how these pressure oscillations affect the in-cylinder heat transfer and what the best approach is to model the heat transfer during ringing combustion. The heat transfer is measured with a thermopile heat flux sensor inside a CFR engine converted to HCCI operation. A variation of the mass fuel rate at different compression ratios is performed to measure the heat transfer during three different operating conditions: no, light and severe ringing. The occurrence of ringing increases both the peak heat flux and the total heat loss.
Technical Paper

Demonstrating the Use of Thin Film Gauges for Heat Flux Measurements in ICEs: Measurements on an Inlet Valve in Motored Operation

2016-04-05
2016-01-0641
To optimize internal combustion engines (ICEs), a good understanding of engine operation is essential. The heat transfer from the working gases to the combustion chamber walls plays an important role, not only for the performance, but also for the emissions of the engine. Besides, thermal management of ICEs is becoming more and more important as an additional tool for optimizing efficiency and emission aftertreatment. In contrast little is known about the convective heat transfer inside the combustion chamber due to the complexity of the working processes. Heat transfer measurements inside the combustion chamber pose a challenge in instrumentation due to the harsh environment. Additionally, the heat loss in a spark ignition (SI) engine shows a high temporal and spatial variation. This poses certain requirements on the heat flux sensor. In this paper we examine the heat transfer in a production SI ICE through the use of Thin Film Gauge (TFG) heat flux sensors.
Technical Paper

Experimental Investigation of a DISI Production Engine Fuelled with Methanol, Ethanol, Butanol and ISO-Stoichiometric Alcohol Blends

2015-04-14
2015-01-0768
Stricter CO2 and emissions regulations are pushing spark ignition engines more and more towards downsizing, enabled through direct injection and turbocharging. The advantages which come with direct injection, such as increased charge density and an elevated knock resistance, are even more pronounced when using low carbon number alcohols instead of gasoline. This is mainly due to the higher heat of vaporization and the lower air-to-fuel ratio of light alcohols such as methanol, ethanol and butanol. These alcohols are also attractive alternatives to gasoline because they can be produced from renewable resources. Because they are liquid, they can be easily stored in a vehicle. In this respect, the performance and engine-out emissions (NOx, CO, HC and PM) of methanol, ethanol and butanol were examined on a 4 cylinder 2.4 DI production engine and are compared with those on neat gasoline.
Technical Paper

The Behavior of a Simplified Spray Model for Different Diesel and Bio-Diesel Surrogates

2015-04-14
2015-01-0950
The need for simulation tools for the internal combustion engine is becoming more and more important due to the complex engine design and increasingly strict emission regulation. One needs accurate and fast models, but fuels consist of a complex mixture of different molecules which cannot realistically be handled in computations. Simplifications are required and are realized using fuel surrogates. The main goal of this work is to show that the choice of the surrogates is of importance if simplified models are used and that the performance strongly depends upon the sensitivity of the fuel properties that refer to the main model hypotheses. This paper starts with an overview of surrogates for diesel and bio-diesel as well as the motivation for choosing them. Next, a phenomenological model for vaporizing fuel-sprays is implemented to assess how well-known surrogates for diesel and bio-diesel affect the obtained results.
Technical Paper

Assessment of Empirical Heat Transfer Models for a CFR Engine Operated in HCCI Mode

2015-04-14
2015-01-1750
Homogeneous charge compression ignition (HCCI) engines are a promising alternative to traditional spark- and compression-ignition engines, due to their high thermal efficiency and near-zero emissions of NOx and soot. Simulation software is an essential tool in the development and optimization of these engines. The heat transfer submodel used in simulation software has a large influence on the accuracy of the simulation results, due to its significant effect on the combustion. In this work several empirical heat transfer models are assessed on their ability to accurately predict the heat flux in a CFR engine during HCCI operation. Models are investigated that are developed for traditional spark- and compression-ignition engines such as those from Annand [1], Woschni [2] and Hohenberg [3] and also models developed for HCCI engines such as those from Chang et al. [4] and Hensel et al. [5].
Journal Article

Calibration of a TFG Sensor for Heat Flux Measurements in a S.I. Engine

2015-04-14
2015-01-1645
In the development of internal combustion engines, measurements of the heat transfer to the cylinder walls play an important role. These measurements are necessary to provide data for building a model of the heat transfer, which can be used to further develop simulation tools for engine optimization. This research will focus on the Thin Film Gauge (TFG) heat flux sensor. This sensor consists of a platinum RTD (Resistance Temperature Detector) on an insulating Macor® (ceramic) substrate. The sensor has a high frequency response (up to 100 kHz) and is small and robust. These properties make the TFG sensor adequate for measurements in the combustion chamber of an internal combustion engine. To use this sensor, its thermal properties - namely the temperature sensitivity coefficient and the thermal product - must be correctly calibrated. First, different calibration setups with a different temperature range are used to calibrate the temperature sensitivity coefficient of the TFG sensor.
Technical Paper

Design of a Fast Responding Start-Up Mechanism for Bi-Propellant Fueled Engine for Miniature UAV Applications

2013-09-17
2013-01-2305
In this work a new design of a liquid fuelled combustion engine is proposed for small and light weight unmanned air vehicles (<10kg and 15-200N thrust). Ethanol and gasoline were selected as the potential fuels while pressurized air and hydrogen peroxide were used as the oxidizer. The engine combines features of both a common rocket and turbojet engine. The main features of the engine are the restart ability during flight, low cost, easy manufacturability, light weight, long operation time and high durability. The main difficulties that come along with this engine are the need for proper engine cooling (long term operation) and start-up ability at atmospheric conditions. The low temperatures and injection pressures are not favorable for the fuel atomization and ignition. The paper focuses on the design on low pressure injectors and a start-up mechanism for micro UAV's without the use of a large amount of additional fueling circuits or components.
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