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Modelling of a Discrete Variable Compression Ratio (VCR) System for Fuel Consumption Evaluation - Part 2: Modelling Results

Luca Barazzoni
Oakland University-Brian Sangeorzan, Dan DelVescovo
Published 2019-04-02 by SAE International in United States
Variable Compression Ratio systems are an increasingly attractive solution for car manufacturers in order to reduce vehicle fuel consumption. By having the capability to operate with a range of compression ratios, engine efficiency can be significantly increased by operating with a high compression ratio at low loads, where the engine is normally not knock-limited, and with a low compression ratio at high load, where the engine is more prone to knock. In this way, engine efficiency can be maximized without sacrificing performance. This study aims to analyze how the effectiveness of a VCR system is affected by various powertrain and vehicle parameters. By using a Matlab model of a VCR system developed in Part 1 of this work, the influence of the vehicle characteristics, the drive cycle, and of the number of stages used in the VCR system was studied. This model takes as inputs: a switching time for the VCR system, the vehicle characteristics, the engine performance maps corresponding to the distinct compression ratios utilized and a vehicle drive cycle.The impact of the vehicle…
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Modelling of a Discrete Variable Compression Ratio (VCR) System for Fuel Consumption Evaluation - Part 1: Model Development

Luca Barazzoni
Oakland University-Brian Sangeorzan, Dan DelVescovo
Published 2019-04-02 by SAE International in United States
Given increasingly stringent emission targets, engine efficiency has become of foremost importance. While increasing engine compression ratio can lead to efficiency gains, it also leads to higher in-cylinder pressure and temperatures, thus increasing the risk of knock. One potential solution is the use of a Variable Compression Ratio system, which is capable of exploiting the advantages coming from high compression ratio while limiting its drawbacks by operating at low engine loads with a high compression ratio, and at high loads with a low compression ratio, where knock could pose a significant threat. This paper describes the design of a model for the evaluation of fuel consumption for an engine equipped with a VCR system over representative drive cycles. The model takes as inputs; a switching time for the VCR system, the vehicle characteristics, engine performance maps corresponding to two different compression ratios, and a drive cycle. Two different types of transmission, a Continuously Variable Transmission and a Step Ratio Transmission, were also considered in the model.As an initial step, the compression ratio switching time was…
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Prediction of Autoignition and Flame Properties for Multicomponent Fuels Using Machine Learning Techniques

Oakland University-Neel Shah, Peng Zhao, Dan DelVescovo
Texas Tech University-Haiwen Ge
Published 2019-04-02 by SAE International in United States
Machine learning methods, such as decision trees and deep neural networks, are becoming increasingly important and useful for data analysis in various scientific fields including dynamics and control, signal processing, pattern recognition, fluid mechanics, and chemical synthesis, etc. For future engine design and performance optimization, there is an urgent need for a robust predictive model which could capture the major combustion properties such as autoignition and flame propagation of multicomponent fuels under a wide range of engine operating conditions, without massive experimental measurement or computational efforts. It will be shown that these long-held limitations and challenges related to complex fuel combustion and engine research could be readily solved by implementing machine learning methods. In this paper, both random forest and deep neural network algorithms were implemented to predict ignition delay times, flame speeds, octane ratings, and CA50 values (crank angle corresponding to 50% of the heat release rate) in homogenous charge compression ignition (HCCI) engines for multicomponent gasoline surrogates. Various training models were first tested to optimize CPU efficiency while maximizing accuracy and reducing error,…
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Design and Validation of a GT Power Model of the CFR Engine towards the Development of a Boosted Octane Number

Oakland University-Saif Salih, Dan DelVescovo
Published 2018-04-03 by SAE International in United States
Developments in modern spark ignition (SI) engines such as intake boosting, direct-injection, and engine downsizing techniques have demonstrated improved performance and thermal efficiency, however, these strategies induce significant deviation in end-gas pressure/temperature histories from those of the traditional Research and Motor Octane Number (RON and MON) standards. Attempting to extrapolate the anti-knock performance of fuels tested under the traditional RON/MON conditions to boosted operation has yielded mixed results in both SI and advanced compression ignition (ACI) engines. This consideration motivates the present work with seeks to establish a pathway towards the development of the test conditions of a boosted octane number, which would better correlate to fuel performance at high intake pressure conditions.In this work, a one dimensional engine model was developed in GT-Power of the cooperative fuel research (CFR) engine following the standard conditions of the RON and MON methods (ASTM 2699 and ASTM 2700 respectively), and validated with experimental data sourced from the relevant literature. The full-flow model utilizes the built-in predictive SI flame propagation model with coefficients tuned to match experimental data,…
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The Effects of Charge Preparation, Fuel Stratification, and Premixed Fuel Chemistry on Reactivity Controlled Compression Ignition (RCCI) Combustion

SAE International Journal of Engines

Oakland University-Dan DelVescovo
University of Wisconsin-Sage Kokjohn, Rolf Reitz
  • Journal Article
  • 2017-01-0773
Published 2017-03-28 by SAE International in United States
Engine experiments were conducted on a heavy-duty single-cylinder engine to explore the effects of charge preparation, fuel stratification, and premixed fuel chemistry on the performance and emissions of Reactivity Controlled Compression Ignition (RCCI) combustion. The experiments were conducted at a fixed total fuel energy and engine speed, and charge preparation was varied by adjusting the global equivalence ratio between 0.28 and 0.35 at intake temperatures of 40°C and 60°C. With a premixed injection of isooctane (PRF100), and a single direct-injection of n-heptane (PRF0), fuel stratification was varied with start of injection (SOI) timing. Combustion phasing advanced as SOI was retarded between -140° and -35°, then retarded as injection timing was further retarded, indicating a potential shift in combustion regime. Peak gross efficiency was achieved between -60° and -45° SOI, and NOx emissions increased as SOI was retarded beyond -40°, peaking around -25° SOI. Optimal cases in terms of both gross efficiency and peak pressure rise rate (PPRR) were in the mid-range SOI timings centered about -50° SOI, while late SOI resulted in decreased gross efficiency,…
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The Development of an Ignition Delay Correlation for PRF Fuel Blends from PRF0 (n-Heptane) to PRF100 (iso-Octane)

SAE International Journal of Engines

University of Wisconsin-Dan DelVescovo, Sage Kokjohn, Rolf Reitz
  • Journal Article
  • 2016-01-0551
Published 2016-04-05 by SAE International in United States
A correlation was developed to predict the ignition delay of PRF blends at a wide range of engine-relevant operating conditions. Constant volume simulations were performed using Cantera coupled with a reduced reaction mechanism at a range of initial temperatures from 570-1860K, initial pressures from 10-100atm, oxygen mole percent from 12.6% to 21%, equivalence ratios from 0.30-1.5, and PRF blends from PRF0 to PRF100. In total, 6,480 independent ignition delay simulations were performed.The correlation utilizes the traditional Arrhenius formulation; with equivalence ratio (φ), pressure (p), and oxygen mole percentage (xo2) dependencies. The exponents α, β, and γ were fitted to a third order polynomial with respect to temperature with an exponential roll-off to a constant value at low temperatures to capture the behavior expressed by the reaction mechanism. The location and rate of the roll-off functions were modified by linear functions of PRF. The activation energy term, λ is expressed as a combination of a third and second order polynomial with respect to temperature with an exponential roll-off function whose location and rate varied with a…
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ERRATUM: The Development of an Ignition Delay Correlation for PRF Fuel Blends from PRF0 (n-Heptane) to PRF100 (iso-Octane)

SAE International Journal of Engines

University of Wisconsin-Dan DelVescovo, Sage Kokjohn, Rolf D. Reitz
  • Journal Article
  • 2016-01-0551.01
Published 2016-04-05 by SAE International in United States
In Equation 10, there should be a plus sign between the first summation term and the quantity in brackets. The acceleration of the participant's vehicle was varied from −0.04 m/s2 to +0.06 m/s2 linearly as a function of the angle of the gas pedal with a 0.1-second delay.
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Numerical Study of RCCI and HCCI Combustion Processes Using Gasoline, Diesel, iso-Butanol and DTBP Cetane Improver

SAE International Journal of Engines

Tianjin Univ.-Mingfa Yao
Univ. of Wisconsin-Dan DelVescovo, Rolf D. Reitz
  • Journal Article
  • 2015-01-0850
Published 2015-04-14 by SAE International in United States
Reactivity Controlled Compression Ignition (RCCI) has been shown to be an attractive concept to achieve clean and high efficiency combustion. RCCI can be realized by applying two fuels with different reactivities, e.g., diesel and gasoline. This motivates the idea of using a single low reactivity fuel and direct injection (DI) of the same fuel blended with a small amount of cetane improver to achieve RCCI combustion. In the current study, numerical investigation was conducted to simulate RCCI and HCCI combustion and emissions with various fuels, including gasoline/diesel, iso-butanol/diesel and iso-butanol/iso-butanol+di-tert-butyl peroxide (DTBP) cetane improver. A reduced Primary Reference Fuel (PRF)-iso-butanol-DTBP mechanism was formulated and coupled with the KIVA computational fluid dynamic (CFD) code to predict the combustion and emissions of these fuels under different operating conditions in a heavy duty diesel engine. The results show that RCCI combustion is achievable by applying a single low reactivity fuel combined with small amount of DTBP cetane improver over wide operating conditions, and that the performance of the iso-butanol-DTBP fuel is comparable to that of gasoline-diesel and iso-butanol-diesel…
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Isobutanol as Both Low Reactivity and High Reactivity Fuels with Addition of Di-Tert Butyl Peroxide (DTBP) in RCCI Combustion

SAE International Journal of Fuels and Lubricants

University of Wisconsin-Dan DelVescovo, Hu Wang, Martin Wissink, Rolf D. Reitz
  • Journal Article
  • 2015-01-0839
Published 2015-04-14 by SAE International in United States
Engine experiments and multi-dimensional modeling were used to explore the effects of isobutanol as both the high and low reactivity fuels in Reactivity Controlled Compression Ignition (RCCI) Combustion. Three fuel combinations were examined; EEE/diesel, isobutanol/diesel, and isobutanol/isobutanol+DTBP (di-tert butyl peroxide). In order to assess the relative performance of the fuel combinations of interest under RCCI operation, the engine was operated under conditions representative of typical low temperature combustion (LTC). A net load of 6 bar indicated mean effective pressure (IMEP) was chosen because it provides a wide operable range of equivalence ratios and combustion phasings without excessively high peak pressure rise rates (PPRR). The engine was operated under various intake pressures with global equivalence ratios from 0.28-0.36, and various combustion phasings (defined by 50% mass fraction burned-CA50) from about 1.5 to about 10 deg after top dead center (ATDC). Combustion phasing was varied by scaling the direct-injected fuel quantity appropriately.Due to isobutanol's high octane number, a significantly larger quantity of direct-injected fuel was required to match combustion phasing, resulting in higher NOx emissions and decreased…
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Improving the Understanding of Intake and Charge Effects for Increasing RCCI Engine Efficiency

SAE International Journal of Engines

University of Wisconsin-Derek Splitter, Martin Wissink, Dan DelVescovo, Rolf D. Reitz
  • Journal Article
  • 2014-01-1325
Published 2014-04-01 by SAE International in United States
The present experimental engine efficiency study explores the effects of intake pressure and temperature, and premixed and global equivalence ratios on gross thermal efficiency (GTE) using the reactivity controlled compression ignition (RCCI) combustion strategy. Experiments were conducted in a heavy-duty single-cylinder engine at constant net load (IMEPn) of 8.45 bar, 1300 rev/min engine speed, with 0% EGR, and a 50% mass fraction burned combustion phasing (CA50) of 0.5°CA ATDC. The engine was port fueled with E85 for the low reactivity fuel and direct injected with 3.5% 2-ethylhexyl nitrate (EHN) doped into 91 anti-knock index (AKI) gasoline for the high-reactivity fuel. The resulting reactivity of the enhanced fuel corresponds to an AKI of approximately 56 and a cetane number of approximately 28.The engine was operated with a wide range of intake pressures and temperatures, and the ratio of low- to high-reactivity fuel was adjusted to maintain a fixed speed-phasing-load condition. This allowed for the investigation of several combinations of intake temperature, intake pressure, and charge stratification at otherwise constant thermodynamic conditions. The results show that sources…
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