Bar Brake Mean Effective Pressure Research Articles

Evaluation of comparative engine combustion, performance and emission characteristics of low temperature combustion (PCCI and RCCI) modes

In this study, a comparative investigation of engine combustion, performance and emission characteristics of low temperature combustion modes namely premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) with conventional compression ignition (CI) combustion mode was performed. Experiments were performed in a single cylinder research engine at constant engine speed (1500 rpm) and at four different engine loads (1, 2, 3 and 4 bar brake mean effective pressure (BMEP)). Baseline CI and PCCI mode combustion experiments were performed using mineral diesel as test fuel; while mineral diesel-methanol fuel pair was used as high-reactivity fuel (HRF) and low-reactivity fuel (LRF) respectively in RCCI mode combustion. Results showed that RCCI mode combustion was relatively more stable compared to baseline CI and PCCI combustion modes. At higher engine loads, RCCI mode combustion exhibited relatively lower knocking and combustion noise than other combustion modes. Performance characteristics showed that brake thermal efficiency (BTE) of RCCI mode combustion was comparable to baseline CI mode combustion, however, at higher engine loads, RCCI mode combustion resulted in relatively higher BTE compared to both baseline CI and PCCI combustion modes. Significantly lower EGT of RCCI mode combustion compared to baseline CI as well as PCCI combustion modes was another important finding of this study. Emission results showed that RCCI mode combustion emitted relatively lower oxides of nitrogen (NOx), but significantly higher hydrocarbons (HC) compared to baseline CI and PCCI combustion modes. A NOx-BTE trade-off analysis was also carried out, which demonstrated the suitability of RCCI mode combustion at all engine loads. Finally, a parametric analysis was carried out to compare the critical parameters of baseline CI, PCCI, and RCCI combustion modes at low and high engine loads, which exhibited improved engine performance and emission characteristics of low temperature combustion (LTC) modes, especially the RCCI mode combustion.

Improving the thermal efficiency of a T-GDI engine using hydrogen from combined steam and partial oxidation exhaust gas reforming of gasoline under low-load stoichiometric conditions

Hydrogen (H2) addition is known to have features of increasing the laminar burning velocity (Di Sarli and Di Benedetto, 2007), the resistance of the flame to strain-induced extinction (Di Sarli and Di Benedetto, 2012, 2013), and also enlarging the operating window of stable combustion (Di Sarli, 2014). We experimentally investigated how to improve the thermal efficiency of a turbo gasoline direct injection (T-GDI) engine using H2 from combined steam and partial oxidation exhaust gas gasoline reforming under low-load stoichiometric conditions. During real driving, 4 and 6 bar brake mean effective pressure (BMEP) at 2,000 rpm are frequently used. Our experimental results show that reformed H2 improves the brake thermal efficiency (BTE) of T-GDI engines operating at 4 and 6 bar BMEP. Furthermore, the combustion speed (increasing heat release rate) and stability (reducing cyclic variation) were enhanced by reformed H2, making more heavy exhaust gas recirculation (EGR) operation. Combining steam and partial oxidation exhaust gas gasoline reforming with extra air injection to a reformer had a large effect on the fuel conversion efficiency of the reformer as the engine load decreased. Therefore, the BTE of the T-GDI engine with combined steam and partial oxidation reforming achieved further improvement over steam reforming only at 4 bar BMEP. Nitrogen oxide (NOX) emissions increased with reformed H2. However, on the basis of the improved combustion stability achieved using reformed H2, NOX emissions could be reduced further by using a higher EGR rate while enhancing the BTE.

Utilizing Exhaust Valve Opening Modulation for Fast Warm-up of Exhaust After-treatment Systems on Highway Diesel Vehicles

Current on-road vehicles are generally outfitted with exhaust after-treatment (EAT) systems to meet the stringent emission regulations. At cold start and low-loaded operations, those systems need to be warmed up above a threshold temperature (generally 250oC) for effective performance. High exhaust temperatures and high exhaust flow rates are required to accelerate the EAT warm up which are mostly not available at low-loaded diesel vehicle operations. Therefore, the objective of this work is to improve EAT warm up at low loads through utilizing exhaust valve opening (EVO) modulation which allows both elevated exhaust temperatures and exhaust flow rates. A 1-D engine simulation program is used to model the system which is set to operate at 1200 RPM engine speed and at 2.5 bar brake mean effective pressure (BMEP) engine load. Exhaust temperature can be increased above 250oC via either early or late EVO timings. Reduced expansion work in advanced EVO timings and increased pumping loss in retarded EVO timings require higher fuel consumption (up to 15 % and 20 %, respectively) to keep engine load constant. Those high fuel penalties reduce engine air-to-fuel ratio and rise exhaust temperature more than 55oC. Exhaust mass flow rate is improved up to 9 % in the system as well. The method increases exhaust gas energy up to 40 % and rises heat transfer rate to the EAT system up to 140 % compared to nominal condition. The technique is highly effective at heating up EAT systems, however, it also causes high fuel inefficiency which needs to be considered.

An exergy analysis methodology for internal combustion engines using a multi-zone simulation of dual fuel low temperature combustion

Increasing fuel efficiency of internal combustion (IC) engines is an imperative economic and environmental need. To this end, in the present work, an exergy analysis methodology was developed and incorporated within a previously validated, closed cycle, multi-zone, thermodynamic simulation of diesel-methane dual fuel low temperature combustion (LTC). To study in-cylinder exergy transformation, the diesel start of injection (SOI) was varied from 300 crank angle degrees (CAD) to 340 CAD for a fixed engine load 6 bar brake mean effective pressure (BMEP) and speed (1700 rev/min). Gross indicated fuel conversion efficiency (iFCE) and exergetic efficiency (including exhaust exergy at exhaust valve opening) were computed for different SOIs. Results show that at all SOIs ~41–42 percent of the total input exergy was destroyed due to combustion irreversibilities. When combustion started, in-cylinder chemical exergy reduced significantly due to exergy transfers associated with work transfer and heat transfer as well as exergy destruction. While at SOI = 340 CAD (representative of conventional dual fuel combustion), ~14 percent of the fuel chemical exergy exited as exhaust physical exergy, this reduced to ~5.5 percent at SOI = 300 CAD (representative of dual fuel LTC). The “maximum efficiency SOI” was SOI = 310 CAD with an iFCE of 43.6 percent and an exergetic efficiency of 52.2 percent.

Experimental investigation on combustion and unregulated emission characteristics of butanol-isomer/gasoline blends

Effects of butanol isomers on characteristics of combustion and emission were studied on PFI SI engine. Experiments were operated under the condition of 3 and 5 bar brake mean effective pressure (BMEP) engine loads and different equivalence ratios (φ=0.83−1.25) with engine speed of 1200 r/min using blends made of 70 vol.% gasoline and 30 vol.% butanol isomers (N30, S30, I30 and T30). The results indicated that compared with gasoline, all butanol isomer blends have higher cylinder pressure. N30 has the highest and most advanced peak pressure, and T30 shows a higher brake specific fuel consumption (BSFC) and lower brake thermal efficiency (BTE). N30 presents a lower UHC emissions and I30 has slightly higher CO emissions than other blends. For unregulated emissions, compared with gasoline, butanol isomer blends have higher acetaldehyde, and N30 produces a higher emission of 1,3-butadiene than other blends. A reduction in benzene, toluene, ethylbenzene and xylene (BTEX) has been found with butanol isomer blends.

High Load Expansion of Catalytic EGR-Loop Reforming under Stoichiometric Conditions for Increased Efficiency in Spark Ignition Engines

<div class="section abstract"><div class="htmlview paragraph">The use of fuel reformate from catalytic processes is known to have beneficial effects on the spark-ignited (SI) combustion process through enhanced dilution tolerance and decreased combustion duration, but in many cases reformate generation can incur a significant fuel penalty. In a previous investigation, the researchers showed that, by controlling the boundary conditions of the reforming catalyst, it was possible to minimize the thermodynamic expense of the reforming process, and in some cases, realize thermochemical recuperation (TCR), a form of waste heat recovery where exhaust heat is converted to usable chemical energy. The previous work, however, focused on a relatively light-load engine operating condition of 2000 rpm, 4 bar brake mean effective pressure (BMEP). The present investigation demonstrates that this operating strategy is applicable to higher engine loads, including boosted operation up to 10 bar BMEP. By controlling the reforming catalyst boundary conditions, it is possible to achieve fuel reforming without experiencing high temperature exotherms that could be damaging to the catalyst. Additionally, the thermodynamic air handling consequences of operating a highly dilute strategy at high loads is quantified. The results confirm that this operating strategy provides an efficiency benefit at all conditions investigated, with relative efficiency increases of 3-6%, and is therefore applicable over wider regions of the engine operating map.</div></div>

Testing of anisole and methyl acetate as additives to diesel and biodiesel fuels in a compression ignition engine

This paper investigates the effects of anisole and methyl acetate (as fuel additives) on the performance and emission characteristics of a compression-ignition (i.e., diesel) engine. Anisole and methyl acetate can be obtained from methylation of phenol and acetic acid, respectively. Phenol and acetic acid are compounds which are abundant in bio-oil derived from pyrolysis of wood and is thus renewable in nature. Using methyl acetate as a diesel fuel additive in compression-ignition engines has rarely been reported in the literature. The objective of the current work is to provide testing results of methyl acetate and perform comparisons with anisole as fuel additives for both diesel and biodiesel fuels. The effects of loads, additive type, and base fuels were tested. The tested loads include 0, 1.26, 2.52, and 3.78 bar brake mean effective pressure (BMEP) and the base fuels include No.2 diesel and biodiesel from waste cooking oil. The additive concentrations were kept at 10% by volume. Engine performance, exhaust emissions, and in-cylinder combustion were measured and analyzed. For diesel-anisole (DA) blends, it was seen that the blends were comparable to diesel in terms of performance but with slightly higher fuel consumption rates. HC and CO emissions reduced slightly, however, NOx and soot concentration increased. Diesel-methyl acetate (DM) blends were comparable to diesel in terms of performance with a slight increase in the fuel consumption rates. HC and CO emissions decreased with added methyl acetates. NOx and soot concentration increased. Both anisole and methyl acetate of 10% by volume in biodiesel were tested and it was observed that both blends were slightly better than pure biodiesel in terms of performance. HC and CO emissions reduced for both blends. NOx and soot concentration however increased as compared to pure biodiesel. From the experiments, it is believed that both anisole and methyl acetate can be used as suitable additives to diesel and biodiesel in terms of performance; however, the emissions of NOx and soot can pose a challenge.

Improving Exhaust Temperature Management At Low-loaded Diesel Engine Operations Via Internal Exhaust Gas Recirculation

Modern on-road automotive vehicles mostly utilize exhaust after-treatment (EAT) systems to meet the stringent emission regulations. Although those systems are generally effective to reduce emission rates, they are ineffectual at low loads due to low exhaust temperatures (below 250 o C). This study demonstrates on a diesel engine model that exhaust temperatures can be increased above 250 o C at light loads through internal exhaust gas recirculation (IEGR). Engine system operates at 1700 RPM engine speed and within 2.5-4.5 bar brake mean effective pressure (BMEP) engine load. IEGR increases the amount of in-cylinder hot residual exhaust gases and thus causes a considerable exhaust temperature rise (up to 70 o C). Warmer exhaust system keeps EAT emission conversion efficiency mostly above 90 % and accelerates EAT catalyst bed warm-up through increased (up to 142 %) heat transfer rates. IEGR is not as fuel-consuming as conventional EAT warming techniques and can keep the fuel consumption rise below 5 %.

Effect of acetone-butanol-ethanol (ABE)–gasoline blends on regulated and unregulated emissions in spark-ignition engine

An experimental study was conducted in a port-fuel injection (PFI) spark-ignition (SI) engine fueled with acetone-butanol-ethanol (ABE) and gasoline. 30 vol% ABE blends with different component ratios (A:B:E = 3:6:1, 6:3:1, and 5:14:1), referred to as ABE(3:6:1)30, ABE(6:3:1)30, and ABE(5:14:1)30, were used as test fuels. Additionally, 30 vol% ethanol and 30% vol.% butanol blended with 70 vol% gasoline, referred to as E30 and B30, respectively, were also used as test fuels. Both the regulated emissions, which include unburned hydrocarbons (UHC), carbon monoxide (CO), and nitrogen oxide (NOx), and unregulated emissions, including acetaldehyde, 1,3-butadiene, benzene, toluene, ethylbenzene, and xylene (BTEX), were investigated under various conditions. The experiments were conducted at an engine speed of 1200 rpm and at engine loads of 3, 4, 5, and 6 bar brake mean effective pressure (BMEP) under various equivalence ratios (φ = 0.83–1.25). The results indicated that ABE(6:3:1)30 had the lowest UHC and CO emissions, with ABE(3:6:1)30 having slightly higher NOx emissions. As for unregulated emissions, B30 showed the highest acetaldehyde emission and ABE(6:3:1)30 had the lowest among all the fuel blends. ABE(3:6:1)30 and ABE(6:3:1)30 showed a reduction in 1,3-butadiene emission. Regarding the BTEX emissions, an overall reduction was observed for all the fuel blends, with ABE(3:6:1)30 having shown the lowest BTEX emissions among all the test fuels. The results indicate that ABE could be used as a promising alternative fuel in SI engines, owing to the reduction in emissions.

Investigation of exhaust flow and exergy fluctuations in a diesel engine

In the present study, we investigated cyclic fluctuations of exhaust flow through measured variations in instantaneous pressure of the exhaust manifold and its implications on the exergy (the useful available energy) of exhaust flow of a single cylinder representation of a heavy-duty diesel engine over a range of operating conditions. The engine was operated at a speed of 1500 rpm and at loads of 2.5 bar and 5 bar brake mean effective pressure (BMEP) and different boost pressures (1.2 bar to 2.4 bar). Instantaneous exhaust pressures were measured over 1000 consecutive engine cycles by a piezoresistive exhaust sensor and instantaneous exhaust temperatures as well as mass flow rates were obtained by constructing GT-SUITE models. Cycle to cycle variations in magnitudes of maximum measured exhaust pressure, calculated exhaust temperature and phasing of the blowdown to displacement transition were analyzed. Additionally, cyclic variability in exhaust exergy components, i.e., thermal and mechanical exergies were estimated. The results show that the magnitude of the maximum exhaust pressure increased at higher engine load (i.e., from the average values of 1.63 bar to 2.00 bar at 2.5 bar BMEP to the average values of 1.78 bar to 2.16 bar at 5 bar BMEP). Also, the crank-resolved ensemble exergy rate in the exhaust process was higher at higher engine load and the return maps of the cumulative exergy at both engine loads exhibited a stochastic pattern. Furthermore, the mechanical component of exergy in the exhaust process had lower variations in comparison to the thermal component of exergy at both engine loads.

High-Performance Computing and Analysis-Led Development of High Efficiency Dilute Opposed Piston Gasoline Engine

Pinnacle is developing a multicylinder 1.2 L gasoline engine for automotive applications using high-performance computing (HPC) and analysis methods. Pinnacle and Oak Ridge National Laboratory executed large-scale multidimensional combustion analyses at the Oak Ridge Leadership Computing Facility to thoroughly explore the design space. These HPC-led investigations show high fuel efficiency (∼46% gross indicated efficiency) may be achieved by operating with extremely high charge dilution levels of exhaust gas recirculation (EGR) at a light load key drive cycle condition (2000 RPM, 3 bar brake mean effective pressure (BMEP)), while simultaneously attaining high levels of fuel conversion efficiency and low NOx emissions. In this extremely dilute environment, the flame propagation event is supported by turbulence and bulk in-cylinder charge motion brought about by modulation of inlet port flow. This arrangement produces a load and speed adjustable amalgamation of swirl and counter-rotating tumble which provides the turbulence required to support stable low-temperature combustion. At higher load conditions, the engine may operate at more traditional combustion modes to generate competitive power. In this paper, the numerical results from these HPC simulations are presented. Further HPC simulations and test validations are underway and will be reported in future publications.

Using Machine Learning to Analyze Factors Determining Cycle-to-Cycle Variation in a Spark-Ignited Gasoline Engine

In this work, we have applied a machine learning (ML) technique to provide insights into the causes of cycle-to-cycle variation (CCV) in a gasoline spark-ignited (SI) engine. The analysis was performed on a set of large eddy simulation (LES) calculations of a single cylinder of a four-cylinder port-fueled SI engine. The operating condition was stoichiometric, without significant knock, at a load of 16 bar brake mean effective pressure (BMEP), at an engine speed of 2500 rpm. A total of 123 cycles was simulated. Of these, 49 were run in sequence, while 74 were run in parallel. For the parallel approach, each cycle is initialized with its own synthetic turbulent field to generate CCV, as a part of another work performed by us. In this work, we used 3D information from all 123 cycles to compute flame topology and pre-ignition flow-field metrics. We then evaluated correlations between these metrics and peak cylinder pressure (PCP) employing an ML technique called random forest. The computed metrics form the inputs to the random forest model, and PCP is the output. This model captures the effect of all inputs, as well as interactions between them owing to its decision-tree structure. The goal of this work is to demonstrate (as a first step) that ML models can implicitly learn complex relationships between the pre-ignition flow-fields, the flame shapes, and the eventual outcome of the cycle (whether a cycle will be a high or a low cycle).

Combustion Mode Switching Characteristics of a Medium-Duty Engine Operated in Compression Ignition/PCCI Combustion Modes

Premixed charge compression ignition (PCCI) combustion is a novel combustion concept, which reduces oxides of nitrogen (NOx) and particulate matter (PM) emissions simultaneously. However, PCCI combustion cannot be implemented in commercial engines due to its handicap in operating at high engine loads. This study is focused on the development of hybrid combustion engine in which engine can be operated in both combustion modes, namely, PCCI and compression ignition (CI). Up to medium loads, engine was operated in PCCI combustion and at higher loads, the engine control unit (ECU) automatically switched the engine operation to CI combustion mode. These combustion modes can be automatically switched by varying the fuel injection parameters and exhaust gas recirculation (EGR) by an open ECU. The experiments were carried out at constant engine speed (1500 rpm) and the load was varied from idling to full load (5.5 bar brake mean effective pressure (BMEP)). To investigate the emission and particulate characteristics during different combustion modes and mode switching, continuous sampling of the exhaust gas was done for a 300 s cycle, which was specifically designed for this study. Results showed that PCCI combustion resulted in significantly lower NOx and PM emissions compared to the CI combustion. Lower exhaust gas temperature (EGT) in the PCCI combustion mode resulted in slightly inferior engine performance. Slightly higher concentration of unregulated emission species such as sulfur dioxide (SO2) and formaldehyde (HCHO) in PCCI combustion mode was another important observation from this study. Lower concentration of aromatic compounds in PCCI combustion compared to CI combustion reflected relatively lower toxicity of the exhaust gas. Particulate number-size distribution showed that most particulates emitted in PCCI combustion mode were in the accumulation mode particle (AMP) size range, however, CI combustion emitted relatively smaller sized particles, which were more harmful to the human health. Overall, this study indicated that mode switching has significant potential for application of PCCI combustion mode in production grade engines for automotive sector, which would result in relatively cleaner engine exhaust compared to CI combustion mode engines.

The effect of oxygenate fuels on PN emissions from a highly boosted GDI engine

Gasoline Direct Injection (GDI) engines are increasingly available in the market. Such engines are known to emit more Particulate Matter (PM) than their port-fuel injected predecessors. There is also a widespread use of oxygenate fuels in the market, up to blends of E85, and their impact on PN emissions is widely studied. However the impact of oxygenate fuels on PN emissions from downsized, and hence highly-boosted engines is not known.In this work, PN emissions from a highly boosted engine capable of running at up to 35 bar Brake Mean Effective Pressure (BMEP) have been measured from a baseline gasoline and three different oxygenate fuels (E20, E85, and GEM – a blend of gasoline, ethanol, and methanol) using a DMS500. The engine has been run at four different operating points, and a number of engine parameters relevant to highly-boosted engines (such as EGR, exhaust back pressure, and lambda) have been tested – the PN emissions and size distributions have been measured from all of these.The results show that the oxygenate content of the fuel has a very large impact on its PN emissions, with E85 giving low levels of PN emissions across the operating range, and GEM giving very low and extremely high levels of PN emissions depending on operating point. These results have been analysed and related back to key fuel properties.

Crank angle-resolved exergy analysis of exhaust flows in a diesel engine from the perspective of exhaust waste energy recovery

Exhaust waste energy recovery (WER) is a critical component in the portfolio of efficiency improvement strategies being considered for internal combustion engines. This paper addresses an important existing knowledge gap by introducing a methodology for performing crank angle-resolved exergy analysis of exhaust flows from the perspective of exhaust WER in diesel engines. To this end, a single-cylinder research engine (SCRE) operating in conventional diesel combustion mode was tested at a load of 5 bar brake mean effective pressure (BMEP), speeds of 1200 and 1500 rpm, and boost pressures of 1.2, 1.5, 2, and 2.4 bar. The crank angle-resolved specific exergy and its thermal and mechanical components were calculated by combining experimental crank angle-resolved exhaust manifold pressure measurements with 1D system-level (GT-POWER) simulations. In addition, exhaust flow specific exergies in the “blowdown” and “displacement” phases of the exhaust process, the total exergy flow rates, and cumulative (time-integrated) exergy were quantified. The results obtained show that low boost pressures led to the highest crank angle-resolved specific exergy, the lowest specific mechanical exergy, and the highest specific thermal exergy. In general, the specific thermal exergy was dominant during the initial phase of the exhaust process while the specific mechanical exergy became important after peak mass flow rate was attained. Regardless of engine speed, with increasing boost pressure, the mechanical component of the cumulative exergy in the exhaust flow increased while the thermal component decreased. Consequently, the results indicate that highly boosted conditions may be more appropriate for direct WER with positive displacement expanders that leverage the mechanical component of exhaust exergy while low boost operating conditions may be better suited for other WER strategies that utilize the thermal component of exhaust exergy.

Development of an aggressive Miller Cycle engine with extended Late-Intake-Valve-Closing and a two-stage turbocharger

This paper describes the development of an aggressive Miller cycle gasoline engine with stoichiometric combustion, a high expansion ratio of 12.5:1, a 65 crank angle degrees (CAD) longer duration Late-Intake-Valve-Closing (LIVC) cam, and a two-stage turbocharger. The full-load performance and part-load fuel consumption of the baseline and Miller cycle engines were assessed through engine dynamometer testing. The aggressive Miller cycle engine achieved the maximum Brake Mean Effective Pressure (BMEP) of 22 bar at 1500 rpm, which was enabled by the 65 CAD longer duration LIVC cam to further reduce the effective compression for controlling knock and by the two-stage turbocharger to provide significantly higher boost for maintaining and increasing trapped mass. It was shown that the more aggressive Millerization was realized while maintaining the specific output and advantages of current downsized boosted engines, such as lower friction and lower pumping losses. The aggressive Miller cycle engine achieved above 6% brake-specific fuel consumption (BSFC) reduction over the baseline turbocharged spark-ignition engine on average. The 65 CAD longer duration LIVC cam provided the benefit of pumping loss reduction with delayed intake valve closing and the benefit of hot residual dilution with relatively advanced intake cam phasing simultaneously, which provided the significant fuel economy improvement at non-knocking light-load conditions. Even without the latest technology enhancements and friction reduction methods on its base engine hardware, the aggressive Miller cycle engine achieved a very broad BSFC island of 230 g/kWh or lower, with the lowest BSFC of 223 g/kWh at 2000 rpm and 10 bar BMEP.

Analysis and Comparison of the Performance of an Inverted Brayton Cycle and Turbocompounding With Decoupled Turbine and Continuous Variable Transmission Driven Compressor for Small Automotive Engines

For an internal combustion engine, a large quantity of fuel energy (accounting for approximately 30% of the total combustion energy) is expelled through the exhaust without being converted into useful work. Various technologies including turbocompounding and the pressurized Brayton bottoming cycle have been developed to recover the exhaust heat and thus reduce the fuel consumption and CO2 emission. However, the application of these approaches in small automotive power plants has been relatively less explored because of the inherent difficulties, such as the detrimental backpressure and higher complexity imposed by the additional devices. Therefore, research has been conducted, in which modifications were made to the traditional arrangement aiming to minimize the weaknesses. The turbocharger of the baseline series turbocompounding was eliminated from the system so that the power turbine became the only heat recovery device on the exhaust side of the engine, and operated at a higher expansion ratio. The compressor was separated from the turbine shaft and mechanically connected to the engine via continuous variable transmission (CVT). According to the results, the backpressure of the novel system is significantly reduced comparing with the series turbocompounding model. The power output at lower engine speed was also promoted. For the pressurized Brayton bottoming cycle, rather than transferring the thermal energy from the exhaust to the working fluid, the exhaust gas was directly utilized as the working medium and was simply cooled by ambient coolant before the compressor. This arrangement, which is known as the inverted Brayton cycle (IBC) was simpler to implement. Besides, it allowed the exhaust gasses to be expanded below the ambient pressure. Thereby, the primary cycle was less compromised by the bottoming cycle. The potential of recovering energy from the exhaust was increased as well. This paper analyzed and optimized the parameters (including CVT ratio, turbine and compressor speed and the inlet pressure to the bottoming cycle) that are sensitive to the performance of the small vehicle engine equipped with inverted Brayton cycle and novel turbocompounding system, respectively. The performance evaluation was given in terms of brake power output and specific fuel consumption. Two working conditions, full and partial load (10 and 2 bar brake mean effective pressure (BMEP)) were investigated. Evaluation of the transient performance was also carried out. Simulated results of these two designs were compared with each other as well as the performance from the corresponding baseline models. The system models in this paper were built in GT-Power which is a one dimension (1D) engine simulation code. All the waste heat recovery systems were combined with a 2.0 L gasoline engine.

Transient “Single-Fuel” RCCI Operation With Customized Pistons in a Light-Duty Multicylinder Engine

Reactivity controlled compression ignition (RCCI) combustion in a light-duty multicylinder engine (MCE) over transient operating conditions using fast response exhaust unburned hydrocarbon (UHC1), nitric oxide (NO), and particulate matter (PM) measurement instruments was investigated. RCCI has demonstrated improvements in efficiency along with low NOx and PM emissions by utilizing in-cylinder fuel blending, generally using two fuels with different reactivity in order to optimize stratification. In the present work, a “single-fuel” approach for RCCI combustion using port-injected gasoline and direct-injected gasoline mixed with a small amount of the cetane improver 2-ethylhexyl nitrate (EHN) was studied with custom designed, compression ratio (CR) of 13.75:1, pistons under transient conditions. The EHN volume percentage in the mixture for the direct-injected fuel was set at 3%. In an experimental investigation, comparisons were made to transient RCCI combustion operation with gasoline/diesel. The experiments were performed over a step load change from 1 to 4 bar brake mean effective pressure (BMEP) at constant 1500 rev/min on a General Motors (GM) Z19DTH 1.9-L diesel engine. The transients were conducted by changing the accelerator pedal command to provide a desired torque output with a DRIVVEN engine control unit (ECU) that replaced the original Bosch ECU. All relevant engine parameters are adjusted accordingly, based on 2D-tables. Previous to the transient engine operation, four steady-state points were used to obtain performance and emission values. Engine calibration at these four points, as well as the interpolation of the intermediate points, allowed for smooth operation during the instantaneous step changes. Differences between the steady-state and transient results indicate the complexity of transient operation and show the need for additional controls to minimize undesirable effects. The steady-state points were calibrated by modifying the fuel injection strategy (actual start of injection (aSOI) timing, port-fuel injection (PFI) fraction, etc.), exhaust gas recirculation (EGR), and rail pressure in order to obtain predefined values for the crank-angle at 50% of total heat release (CA50). Furthermore, emission targets (HC1 < 1500 ppmC3, NO < 10 ppm, filter smoke number (FSN)<0.1 with a maximum pressure rise rate (MPRR) < 10 bar/deg) and noise level targets (<95 dB) for RCCI combustion were maintained during the calibration and mapping. The tests were performed with a closed-loop (CL) calibration by using a next-cycle (NC) controller to adjust the PFI ratio of each cycle in order to reach the steady-state CA50 values in the table. The results show that single-fuel RCCI operation can be achieved, but requires significant alteration of the operating conditions, and NOx emissions were significantly elevated for gasoline/gasoline–EHN operation. While combustion phasing could not be matched, UHC1 emissions were at a similar level as for gasoline/diesel combustion. It is expected that the implementation of different injection strategies and boosted operation, combined with use of higher compression ratio pistons in order to compensate for the lower reactivity direct injection (DI) fuel, could raise the potential for improved performance.

Use of Adaptive Injection Strategies to Increase the Full Load Limit of RCCI Operation

Dual-fuel combustion using port-injection of low reactivity fuel combined with direct injection (DI) of a higher reactivity fuel, otherwise known as reactivity controlled compression ignition (RCCI), has been shown as a method to achieve low-temperature combustion with moderate peak pressure rise rates, low engine-out soot and NOx emissions, and high indicated thermal efficiency. A key requirement for extending to high-load operation is moderating the reactivity of the premixed charge prior to the diesel injection. One way to accomplish this is to use a very low reactivity fuel such as natural gas. In this work, experimental testing was conducted on a 13 l multicylinder heavy-duty diesel engine modified to operate using RCCI combustion with port injection of natural gas and DI of diesel fuel. Engine testing was conducted at an engine speed of 1200 rpm over a wide variety of loads and injection conditions. The impact on dual-fuel engine performance and emissions with respect to varying the fuel injection parameters is quantified within this study. The injection strategies used in the work were found to affect the combustion process in similar ways to both conventional diesel combustion (CDC) and RCCI combustion for phasing control and emissions performance. As the load is increased, the port fuel injection (PFI) quantity was reduced to keep peak cylinder pressure (PCP) and maximum pressure rise rate (MPRR) under the imposed limits. Overall, the peak load using the new injection strategy was shown to reach 22 bar brake mean effective pressure (BMEP) with a peak brake thermal efficiency (BTE) of 47.6%.

An Experimental Study on the Potential Usage of Acetone as an Oxygenate Additive in PFI SI Engines

To face the challenges of fossil fuel shortage and stringent emission norms, there is growing interest in the potential usage of alternative fuels such as bio-ethanol and bio-butanol in internal combustion engines. More recently, Acetone–Butanol–Ethanol (ABE), the intermediate product of bio-butanol fermentation, has been gaining a lot of attention as an alternative fuel. The literature shows that the acetone in the ABE blends plays an important part in improving the combustion performance and emissions, owing to its higher volatility. Acetone and ethanol are the low-value byproducts during bio-butanol production, so using acetone and ethanol as fuel additives may have both economic and environmental benefits. This study focuses on the differences in combustion, performance and emission characteristics of a port-injection spark-ignition engine fueled with pure gasoline (G100), ethanol-containing gasoline (E10 and E30) and acetone-ethanol-gasoline blends (AE10 and AE30 at A:E volumetric ratio of 3:1). The tests were conducted at 1200 RPM, under gasoline maximum brake torque (MBT) at 3 bar and 5 bar brake mean effective pressure (BMEP). Performance and emission data were measured under various equivalence ratios. Based on the comparison of combustion phasing, brake thermal efficiency, brake specific fuel consumption and various emissions of different fuels, it was found that using acetone as an oxygenate additive with the default ECU calibration (for gasoline) maintained the thermal efficiency and showed lower unburned HC emissions.