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

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In a previous study, it was shown that isobaric combustion cycle, achieved by multiple injection strategy, is more favorable than conventional diesel cycle for the double compression expansion engine (DCEE) concept. In spite of lower effective expansion ratio, the indicated efficiencies of isobaric cycles were approximately equal to those of a conventional diesel cycle. Isobaric cycles had lower heat transfer losses and higher exhaust losses which are advantageous for DCEE since additional exhaust energy can be converted into useful work in the expander. In this study, the performance of low-pressure isobaric combustion (IsoL) and high-pressure isobaric combustion (IsoH) in terms of gross indicated efficiency, energy flow distribution and engine-out emissions is compared to the conventional diesel combustion (CDC) but at a relatively lower compression ratio of 11.5. The experiments are conducted in a Volvo D13C500 single-cylinder heavy-duty engine using standard EU diesel fuel. The current study consists of two sets of experiments. In the first set, the effect of exhaust gas recirculation (EGR) is studied at different combustion modes using the same air-fuel ratio obtained from the preceding work. In the second set of experiments, different injection strategies are investigated for IsoL and IsoH combustion at constant and varying load conditions. From the results, it is found that isobaric combustion has similar or higher gross indicated efficiency than those of CDC. The exhaust losses are higher while the heat transfer losses are lower than CDC, which could be beneficial for DCEE concept. For isobaric cases, the NOx emissions were lower with higher uHC/CO/Soot emissions compared to CDC. From the injection strategy study, it was found that the gross indicated efficiency is highest with three injections i.e. at medium load. The efficiency is lower for both low and high load conditions due to increased exhaust and heat transfer losses, respectively. Also, the gross indicated efficiency is largely unchanged when more than one injection event is executed; however the IsoL yields higher overall emissions as compared to IsoH combustion.

Section: Engine Operating Conditionsmentioning

confidence: 99%

“…Among these combustion technologies, DCEE concept started attracting attention lately. Previous simulation studies [22,[24][25][26][27] suggested that this concept can accomplish a high BTE of 56% at air-fuel ratio of 3.0. In this proposed concept, a lowpressure (LP) and a high-pressure (HP) cylinders.…”

Section: Introductionmentioning

confidence: 99%

Isobaric Combustion at a Low Compression Ratio

Dyuisenakhmetov

Goyal

Houidi

et al. 2020

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“…Using the DCEE concept, Lam et al demonstrated brake efficiencies of 56 % [8] as well as 52.7 % [9]. Further efficiency improvements have then been achieved by Shankar et al [10] with the use of insulation to reduce heat losses. This study proves the importance of heat transfer reductions for this concept.…”

Section: /15/2019mentioning

confidence: 99%

Novel Geometry Reaching High Efficiency for Multiple Injector Concepts

Nyrenstedt

Andersson

2019

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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. The DCEE can re-use the residual exhaust energy for a second expansion meaning increased importance of reduced heat losses. Heat release effects were discarded in the evaluation as an explanation for the reduced heat losses in order to isolate the effects of the changed spray pattern. Results showed a decrease in heat losses by 25.1 % or 4.2 % of the fuel energy as well as an increased IMEP of 4.5 % or 1.9 % of the fuel energy. Together with the increased exhaust energy, results showed a possible total engine efficiency increase of 2.6 % using the DCEE concept. This work successfully proves the benefits of using two injectors with a flat bowl over a standard bowl and the conventional one-injector strategy.

“…Based on this concept, Lam et al [3,4] reported up to 52.7 % brake thermal efficiency for different engine operating conditions. Further efficiency improvement has been demonstrated for the DCEE concept by Shankar et al [5] with the use of insulation to reduce the heat transfer losses.…”

Section: Introductionmentioning

confidence: 99%

CFD Study of Heat Transfer Reduction Using Multiple Injectors in a DCEE Concept

Nyrenstedt

Alturkestani

2019

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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. To isolate the heat losses associated with the changed spray pattern of the two-injector concept, effects of the heat release are excluded during the analysis. Results showed that the optimal injection strategy allows a decrease in the temperature close to the walls, leading to heat loss reduction up to 13 % or 2 % of the fuel energy. The residual exhaust energy was increased by 1.5 %-points with the twoinjector concept when compared to the reference case. This proved the advantage of the two-injector concept compared to conventional single injector case for the DCEE application.