Bar Brake Mean Effective Pressure Research Articles

Investigation of the performance and emissions of a diesel engine fuelled with bio-oil generated through microwave-assisted pyrolysis of a blend of hazelnut, walnut, and polyethylene terephthalate waste

New and renewable energy sources are the most important issue nowadays. Bio-oil which can replace fossil fuel is an alternative source of energy. In this study, the performance effects and emissions of bio-oil produced by microwave-assisted pyrolysis system (MAP) from the walnut shell (WS), hazelnut shell (HS), and polyethylene terephthalate (PET) waste mixtures on a single-cylinder diesel engine were investigated. For this purpose, WS, HS, and PET wastes were mixed in two different proportions and converted into pyrolytic oil in the MAP system at 700 watts of microwave power and a 30-minute retention time. Produced pyrolytic oils were converted into bio-oil as S1 (46.25% WS + 46.25% HS + 2.5% PET) and S2 (43.75% WS + 43.75% HS + 7.5% PET) through a 3-stage basic upgrading steps. Experimental results showed that MAP of mixed WS, HS, and PET resulted in high hydrocarbon content bio-oil. In the engine experiments, bio-oil was mixed with diesel at 10%, 20%, and 30% ratios by volume and used in a diesel engine at different Brake Mean Effective Pressure (BMEP) (1.4, 2, 2.7, and 3.4 bar). Engine performance has been found to be comparable to diesel at low blend percentages. At 3.4 bar BMEP, while the brake-specific fuel consumption (BSFC) of diesel was 712 g/kWh, it was obtained as 832 and 804 g/kWh at S1 and S2, respectively. However, when the emissions were evaluated in general, it was determined that the emission values increased with increasing bio-oil/diesel blend ratios due to the high viscosity, higher density, and low cetane number of bio-oil compared to diesel.

Characterization of Flex-Fuel Prechamber Enabled Mixing-Controlled Combustion With Gasoline/Ethanol Blends at High Load

Abstract This numerical study focuses on the characterization of prechamber-enabled mixing-controlled combustion (PC-MCC) at ∼18 bar brake mean effective pressure (BMEP) and 2200 rpm with 10% by volume ethanol-gasoline blend (E10) and pure ethanol (E100). Computational fluid dynamic (CFD) simulations of a stock and prechamber retrofitted single-cylinder Caterpillar C9.3B are carried out using CONVERGE. Prechamber equivalence ratio at spark timing, prechamber spark timing advance, and main chamber injection strategy are assessed with respect to their impact on ignition assistance performance and emissions characteristics relative to a diesel baseline at the same boundary conditions. Simulation results indicate that PC-MCC is flex-fuel capable and operates well for both E10 and E100 at the operating conditions considered. The results demonstrate that the use of a pilot-main injection strategy enables spark timing in the prechamber to be advanced and thus reduces spark plug firing pressure while maintaining robust ignition assistance. Results also indicate that the rich prechamber operation is favored for improved ignition assistance capabilities. The findings of this work suggest that a heavy-duty vehicle using a PC-MCC engine can utilize any blend of gasoline and ethanol, up to including pure ethanol, with no major sacrifices in performance relative to the diesel engine.

Exploring the Benefits of Karanja-Oil-Derived Biodiesel-Water Emulsion as a Potential Fuel for Diesel Engines Operated with High-Pressure Fuel Injection Systems

<div>Biodiesel is a suitable alternative to diesel because of its carbon neutrality, renewability, lubricity, and lower pollutant emissions. However, extensive research indicates higher oxides of nitrogen (NO<sub>x</sub>) emissions with biodiesel. A practical method to combat this problem is utilizing water and biodiesel as emulsions. The effect of biodiesel-water emulsion in high-pressure fuel injection systems is not fully explored in the existing literature. The present study addresses this research gap by utilizing biodiesel-water emulsions in a modified light-duty diesel engine. The governor-controlled injection system was adapted to a fully flexible electronic system capable of high-pressure injection. Unlike other literature studies, the fuel injection timings were optimized with biodiesel-water emulsions to maximize brake thermal efficiency (bte) at every load condition. In a novel attempt, the biodiesel source, i.e., raw Karanja oil (RKO), a triglyceride, was utilized as the surfactant to stabilize the biodiesel-water emulsions containing 6%, 12%, and 18% water. The emulsions reduced the ignition delay and cylinder pressures, with less-intense premixed combustion and a more significant diffusion phase combustion than biodiesel. The emulsions also present a delayed combustion phasing following the injection timing trends. Among the tested emulsions, at 5.08 bar brake mean effective pressure (BMEP), 18% biodiesel-water emulsion resulted in an 18% reduced brake specific fuel consumption (bsfc), 5% increase in bte, 30% and 7% mitigation in NO<sub>x</sub> and smoke levels, with an increase of 10% and 28% for unburned hydrocarbon (HC) and carbon monoxide (CO) emissions.</div>

Effect of early intake valve closing, exhaust gas recirculation and split injection on combustion and emissions characteristics of a HDDI diesel engine operating in PCCI combustion mode

Premixed Charge Compression Ignition (PCCI) combustion is an alternative to conventional diffusion-controlled combustion for Mono-nitrogen oxides (NOx) and soot emissions reduction in DI diesel engines. However, bringing the center of combustion (CoC) near top dead center (TDC) to reduce brake specific fuel consumption is challenging. In this study, for two Early Intake Valve Closing (EIVC) profiles of split injection strategy, combustion characteristics and emissions of a heavy-duty direct injection (HDDI) diesel engine are evaluated by CFD simulations. Combustion efficiency, Indicated Specific Fuel Consumption (ISFC), NOx, soot, and carbon monoxide (CO) emissions are evaluated for 40 ˚CA and 80˚CA EIVC timings with respect to the base diesel combustion with 0, 30, 50, and 70% Exhaust Gas Recirculation (EGR) rates at 3 bar Brake Mean Effective Pressure (BMEP).CFD simulations reveal that EIVC strategy can displace the CoC towards TDC up to 5–10 ˚CA depending on the EGR rate. Moreover, up to 30% NOx reduction can be achieved in EIVC cases. In 70% EGR case, lower ISFC and near zero NOx emissions can be obtained compared to conventional diesel combustion due to CoC being closer to TDC. However, the EIVC strategy with EGR increases CO emissions due to incomplete combustion of a lower air/fuel ratio mixture.

Cyclic Combustion Variability of Dimethyl-Ether-Fueled Agricultural Tractor Engine

Abstract Combustion in dimethyl-ether (DME)-fueled engines needs to be assessed carefully for its widespread acceptability from a drivability viewpoint. Since the test engine used in an off-highway segment, it was tested in a steady-state cycle for engine performance, combustion, emissions, and their cyclic variations, which were the only parameters to assess the drivability. This study investigated and analyzed the cyclic variations of a 100% DME-fueled engine equipped with modified mechanical fuel injection equipment. It was compared with baseline diesel to understand its positive and negative aspects. Experiments were conducted at different engine speeds (1200,1600, and 2000 rpm) and loads (No Load, 1.29, 2.59, 3.88, 5.18, and 6.47 bar brake mean effective pressure (BMEP)) . In-cylinder pressure was recorded for 250 consecutive engine cycles, and many combustion parameters were comparatively analyzed for diesel and DME fuelings. The coefficient of variation (COV) of maximum in-cylinder pressure (Pmax) was lower for DME than diesel at 1600 rpm and comparable at the other remaining engine speeds (1200 and 2000 rpm). Variations in COV of Pmax were higher at low loads and negligible at high loads for both test fuels. At 2000 rpm, the crank angle positions at which Pmax occurred were distributed in a narrow range for DME, representing higher combustion stability than baseline diesel. Variations in the maximum rate of pressure rise (RoPRmax) were lower for DME at 3.88 and 6.47 bar BMEP, while these were higher at 1.29 bar BMEP than baseline diesel. COV of indicated mean effective pressure (COVIMEP) decreased from lower to higher loads for diesel and DME fueling at 1600 and 2000 rpm engine speeds. The differences in COVIMEP between diesel and DME were negligible at higher loads, representing engine stability similar to baseline diesel. Combustion parameters assessed indicated that DME fueling led to lower cyclic variations than baseline diesel as the engine operated from lower to higher loads. At lower loads, DME fueling showed higher cyclic variations than baseline diesel.

Injection system modification and optimization for performance enhancement and emission reduction in a light-duty diesel engine fuelled by biodiesel-water emulsion

In conventional diesel engines, adding water to carbon–neutral biodiesel simultaneously reduces nitrogen oxides (NOx) and smoke emissions whilst improving engine performance. However, such investigations reported in the literature are conducted with engines equipped with a mechanically actuated fuel supply system lacking flexibility in the injection schedule. The present investigation aims at modifying and optimizing an existing mechanical fuel injection system to an electronic common rail injection (CRDi) system for utilizing biodiesel-water emulsion. A light-duty diesel engine's performance and emission characteristics with the modified CRDi system operated with biodiesel-water emulsion is compared with the mechanical injection system. The formulated Karanja biodiesel and water emulsion contained 18 % water, and 2 % of the raw oil was utilized as the stabilizer for the emulsion. The results show that the CRDi system results in lower peak cylinder pressure, higher heat release rates, and retarded combustion phasing for all the tested fuels compared to the mechanical injection counterpart. Compared to diesel with the mechanical injection system, biodiesel-water emulsion with CRDi system reduced fuel consumption and increased thermal efficiency by 30 % and 14 %, respectively, at 5.08 bar brake mean effective pressure (BMEP). The NOx emissions for the emulsion were similar to diesel with the mechanical injection system, whereas a decrease of 29, 30 and 10 % was observed for emissions of smoke, unburned hydrocarbon (HC) and carbon monoxide (CO), respectively. The current investigation reveals that utilizing biodiesel-water emulsion with a flexible injection system reduces engine exhaust emissions while simultaneously improving the performance characteristics.

An Experimental and Computational Study on Triple Injection Strategies to Reduce Cold Start Diesel Engine Emissions

Abstract The effect of triple injection strategies in a diesel engine to reduce cold start emissions were experimentally and computationally investigated in this work. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. As a representative of the cold start condition in the diesel engine, a low load condition of 1500 rpm and 2 bar brake mean effective pressure (BMEP) was chosen as the fixed condition for this study. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injections are fixed and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment system. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The mixture of primary reference fuels (i.e., PRF 34) obtained by matching the cetane number (CN) of diesel fuel, showed similar combustion characteristics of diesel, but is much more volatile due to lighter components in the PRF mixture. The increased volatility of PRF 34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE™. The physical properties of diesel fuel were modeled using a five-component surrogate. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. The simulations were able to capture the experimental trends of combustion characteristics and emissions. The HC emissions were observed to increase for both fuels with retarded post injection timings in engine experiments. PRF 34 had comparable HC emissions to diesel experiments, which indicated that the liner impingement is not the main source of the increase in HC emissions. Overmixing of the fuel and air was identified as the major cause of increase in HC emissions. Additionally, exhaust gas recirculation (EGR) also intensified the overmixing phenomenon and thereby increase in HC emissions.

Emulsification – A promising approach to improve performance and reduce exhaust emissions of a biodiesel fuelled light-duty diesel engine

The effectiveness of employing emulsions prepared with water and ethanol to reduce the inherently higher levels of oxides of nitrogen (NOx) emission with biodiesel, whilst improving or maintaining the smoke emission, is investigated in the present work. To facilitate a one-to-one comparison, the water/ethanol to biodiesel ratio for the emulsions was similar at 18% by mass. Experiments were conducted on a light-duty diesel engine at a constant speed and varying loads with diesel, biodiesel, biodiesel-water and biodiesel-ethanol emulsions. A novel surfactant, Poly Glycerol Poly Ricinoleate (PGPR), was used for preparing biodiesel-water emulsion that exhibited no phase separation for over four months. The results obtained with both emulsions were compared with neat biodiesel as the reference fuel. Ignition delay and peak pressure increased for both emulsions. The biodiesel-water emulsion resulted in advanced combustion phasing while it was retarded with ethanol emulsion. The brake thermal efficiency increased with biodiesel-water emulsion up to 7% at 6.3 bar brake mean effective pressure (BMEP) while at 3% with ethanol emulsion. The brake specific fuel consumption (BSFC) was reduced by 20% with biodiesel-water emulsion, while it remained the same as biodiesel with ethanol emulsion. The emulsions simultaneously reduced NOx and smoke emissions; the biodiesel-water emulsion was more effective, resulting in a maximum reduction of 45% and 37% in NOx and smoke emissions, respectively. The biodiesel-water emulsion also significantly reduced carbon monoxide (CO) emissions, with a maximum reduction of 54% at 6.3 bar BMEP. Overall, the emulsification of biodiesel provides considerable benefits in terms of reduced exhaust emissions and improved engine performance.

Experimental investigations of methanol fumigation via port fuel injection in preheated intake air in a single cylinder dual-fuel diesel engine

Primary alcohols are emerging as promising alternative fuels for diesel engines. Dual-fuel engine operation with port injection (fumigation) of methanol has emerged as a novel concept for simultaneous reduction of particulate matter (PM) and oxides of nitrogen (NOx). This experimental study investigates the effect of intake air preheating on methanol-fumigated agricultural diesel engines. Methanol premixing ratio was kept constant at 50% (M50) for all test conditions. The experiments were performed at a constant speed of 1500 rpm at two intake temperatures of 40 °C and 80 °C, and engine load was varied from 1.25 to 5 bar brake mean effective pressure (BMEP). It was observed that intake air heating influenced the engine’s combustion, performance, and emission characteristics. Higher intake air temperature (M50, 80 °C) resulted in higher peak in-cylinder pressure and brake thermal efficiency (BTE) than the low-temperature case (M50, 40 °C). Higher intake air temperature compensated for the cooling effect due to evaporation of methanol caused by a shorter combustion duration, leading to more efficient energy conversion. Higher hydrocarbons (HC) and carbon monoxide (CO) emissions were observed in addition to lower nitric oxide (NO) emission for M50 vis-a-vis baseline diesel at all loads. The study concluded that intake air temperature significantly affects methanol-diesel dual-fuel engine characteristics and will be an important parameter requiring optimisation before large-scale methanol implementation in agriculture and transport sectors.

Impact of low reactivity fuel type on low load combustion, emissions, and cyclic variations of diesel-ignited dual fuel combustion

In this study, cyclic variations in dual fuel combustion with diesel ignition of three different low reactivity fuels (methane, propane, and gasoline) are examined under identical operating conditions. Experiments were performed on a single cylinder research engine (SCRE) at a low load of 3.3 bar brake mean effective pressure (BMEP). The start of injection (SOI) of diesel was varied from 280 to 330 absolute crank angle degrees (CAD). Engine speed, rail pressure, and boost pressure were held constant at 1500 rpm, 500 bar, and 1.5 bar, respectively. The energy substituted by the low reactivity fuel was fixed at 80% of the total energy input. It was found that diesel-methane (DM) and diesel-propane (DP) combustion were affected by diesel mixing to a greater extent than diesel-gasoline (DG) combustion due to the higher reactivity of gasoline. The magnitude of low temperature heat release was greatest for DG combustion followed by DM and DP combustion for all SOIs. The ignition delay for DG combustion was the shortest, followed by DM and DP combustion. DM and DP combustion exhibited more cyclic variations than DG combustion. Cyclic variations decreased for DM and DP combustion when SOI was advanced; however, DG combustion cyclic variations remained essentially constant for all SOIs. Earlier SOIs (280, 290, 300, and 310 CAD) for DM and (280, 290, and 300 CAD) for DP combustion indicated some prior-cycle effects on the combustion and IMEP (i.e. some level of determinism).

Effects of Intake Valve Lift Form Modulation on Exhaust Temperature and Fuel Economy of a Low-loaded Automotive Diesel Engine

Exhaust after-treatment (EAT) systems on automotive vehicles cannot perform effectively at low loads due to low exhaust temperatures (Texhaust < 250oC). Con-ventional late intake valve closure (LIVC) technique - a proven method to im-prove diesel exhaust temperatures - generally requires the modulation of the whole valve lift profile. However, an alternative method - boot-shaped LIVC - only needs partial lift form modulation and can rise exhaust temperatures signif-icantly. Therefore, this study attempts to demonstrate that boot-shaped LIVC can be an alternative solution to improve exhaust temperatures above 250oC at low-loaded operations of automotive vehicles.A 1-D engine simulation program is used to model the diesel engine system operating at 1200 RPM engine speed and at 2.5 bar brake mean effective pres-sure (BMEP) engine load. Boot-shaped LIVC is achieved via keeping the valve lift constant (at 4.0 mm) for a while during closure and then closing it at different closure angles. The method results in up to 55oC exhaust temperature rise through reduced in-cylinder airflow and thus, is adequate to keep EAT system above 250oC at low loads. The longer the boot is kept during closure, the lower the air-to-fuel ratio is reduced and the higher the exhaust temperature flows at turbine exit. Similar to conventional LIVC, boot-shaped LIVC improves fuel con-sumption as pumping losses are decreased in the system. Despite aforementioned improvements, EAT warm-up is affected negatively due to the significant drop-off on exhaust mass flow rates. The need to modify only some parts of the lift profile is a technical advantage and can reduce production costs.

Investigation and Optimization of Diesel Engine Outputs Under Undi Biodiesel-Diesel Strategies

Abstract The present investigation accentuates the impact of Undi biodiesel blended diesel on combustion, performance, and exhaust fume profiles of a single-cylinder, four-stroke diesel engine. Five Undi biodiesel-diesel blends were prepared and tested at four variable loads over a constant speed of 1500 (±10) rpm. The Undi biodiesel incorporation to diesel notably improved the in-cylinder pressure and heat release rate (HRR) of the engine. The higher amount of Undi biodiesel addition enhanced the brake thermal efficiency (BTE) and brake specific energy consumption (BSEC) of the engine. In addition, the Undi biodiesel facilitated the reduction of the major pollutants, such as unburned hydrocarbon (UHC), carbon monoxide, and particulate matter (PM) emissions with slightly higher oxides of nitrogen emissions of the engine. To this end, a trade-off study was introduced to locate the favorable diesel engine operating conditions under Undi biodiesel-diesel strategies. The optimal results of the engine operation were found to be 32.65% of brake thermal efficiency, 1.21 g/kWh of brake specific cumulated oxides of nitrogen and unburned hydrocarbon, 0.94 g/kWh of brake specific carbon monoxide (BSCO), and 0.32 g/kWh of brake specific particulate matter (BSPM) for 50% (by volume) Undi biodiesel blend at 5.6 bar brake mean effective pressure (BMEP) with a relative closeness value of 0.978, which brings up the pertinence of the trade-off study in diesel engine platforms.

Particulate characteristics of low-temperature combustion (PCCI and RCCI) strategies in single cylinder research engine for developing sustainable and cleaner transportation solution

In this experimental study, particulate matter (PM) characterizations of different low-temperature combustion (LTC) strategies have been compared with conventional compression ignition (CI) combustion for finding out a sustainable and cleaner transport solution. LTC strategies included premixed charge compression ignition (PCCI) and reactivity-controlled compression ignition (RCCI) combustion. Particulate sampling and characterization were carried out in a single-cylinder diesel engine. All engine tests were performed at 1, 2, 3, 4 bar brake mean effective pressure (BMEP) at 1500 rpm. CI and PCCI combustion experiments were performed using mineral diesel as the test fuel. However, mineral diesel and methanol were used as high reactivity fuel (HRF) and low reactivity fuel (LRF), respectively in the RCCI combustion strategy. For all combustion strategies, fuel injection pressure (FIP) was kept constant at 500 bar. However, the number of injections and start of injection (SoI) timings were varied to optimize the engine performance. Results showed that the RCCI combustion strategy emitted a relatively lower concentration of particles than the other two strategies (PCCI and CI). A relatively higher number concentration of accumulation mode particles (AMP) compared to nucleation mode particles (NMP) in the exhaust of the RCCI combustion strategy was an important finding of this study. Number-size and mass-size distributions of particles emitted from different strategies also exhibited the dominant concentration of particles in the CI combustion strategy. PM bound trace metal analysis was yet another critical aspect of this study, which showed that both RCCI and PCCI strategies emitted a relatively lower concentration of trace metals than the conventional CI combustion strategy. Parametric analysis of different PM characteristics and NOx-PM trade-off analysis also demonstrated the importance of LTC strategies over the conventional CI combustion strategy. Overall, this study demonstrated that all LTC strategies could be used for PM and NOx reduction; however, the RCCI combustion strategy was more dominant in NOx and PM reduction, in addition to having an excellent capability of using alternative fuel in the quest for developing sustainable transport solution.

Gasoline Compression Ignition on a Light-Duty Multi-Cylinder Engine Using a Wide Range of Fuel Reactivities and Heavy Fuel Stratification

AbstractMany research studies have focused on utilizing gasoline in modern compression ignition engines to reduce emissions and improve efficiency. Collectively, this combustion mode has become kn+own as gasoline compression ignition (GCI). One of the biggest challenges with GCI operation is maintaining control over the combustion process through the fuel injection strategy, such that the engine can be controlled on a cycle-by-cycle basis. Research studies have investigated a wide variety of GCI injection strategies (i.e., fuel stratification levels) to maintain control over the heat release rate while achieving low-temperature combustion (LTC). This work shows that at loads relevant to light-duty engines, partial fuel stratification (PFS) with gasoline provides very little controllability over the timing of combustion. On the contrary, heavy fuel stratification (HFS) provides very linear and pronounced control over the timing of combustion. However, the HFS strategy has challenges achieving LTC operation due to the air handling burdens associated with the high exhaust gas recirculation (EGR) rates that are required to reduce NOx emissions to near zero levels. In this work, a wide variety of gasoline fuel reactivities (octane numbers ranging from <40 to 87) were investigated to understand the engine performance and emissions of HFS-GCI operation on a multi-cylinder light-duty engine. The results indicate that over an EGR sweep at 4 bar brake mean effective pressure (BMEP), the gasoline fuels can achieve LTC operation with ultra-low NOx and soot emissions, while conventional diesel combustion (CDC) is unable to simultaneously achieve low NOx and soot. At 10 bar BMEP, all the gasoline fuels were compared to diesel, but using mixing controlled combustion and not LTC.

Response surface method optimization of a natural gas engine with dedicated exhaust gas recirculation

Stoichiometric industrial natural gas engines rely on robust design to achieve consumer driven up-time requirements. Key to this design are exhaust components that are able to withstand high combustion temperatures found in this type of natural gas engine. The issue of exhaust component durability can be addressed by making improvements to materials and coatings or decreasing combustion temperatures. Among natural gas engine technologies shown to reduce combustion temperature, dedicated exhaust gas recirculation (EGR) has limited published research. However, due to the high nominal EGR rate it may be a technology useful for decreasing combustion temperature. In previous work by the author, dedicated EGR was implemented on a Caterpillar G3304 stoichiometric natural gas engine. Examination of combustion statistics showed that, in comparison to a conventional stoichiometric natural gas engine, operating with dedicated EGR requires adjustments to the combustion recipe to achieve acceptable engine operation. This work focuses on modifications to the combustion recipe necessary to improve combustion statistics such as coefficient of variance of indicated mean effective pressure (COV of IMEP), cylinder-cylinder indicated mean effective pressure (IMEP), location of 50% mass fraction burned, and 10%–90% mass fraction burn duration. Several engine operating variables were identified to affect these combustion statistics. A response surface method (RSM) optimization was chosen to find engine operating conditions that would result in improved combustion statistics. A third order factorial RSM optimization was sufficient for finding optimized operating conditions at 3.4 bar brake mean effective pressure (BMEP). The results showed that in an engine with a low turbulence combustion chamber, such as a G3304, optimized combustion statistics resulted from a dedicated cylinder lambda of 0.936, spark timing of 45° before top dead center (°bTDC), spark duration of 365 µs, and intake manifold temperature of 62°C. These operating conditions reduced dedicated cylinder COV of IMEP by 10% (absolute) and the difference between average stoichiometric cylinder and dedicated cylinder IMEP to 0.19 bar.

The Rotating Liner Engine (RLE) Diesel Prototype: Reducing Internal Engine Friction by about 40% under Idle Conditions

The Rotating Liner Engine (RLE) concept is a design concept for internal combustion engines, where the cylinder liner rotates at a surface speed of 2–4 m/s in order to assist piston ring lubrication. Specifically, we have evidence from prior art and from our own research that the above rotation has the potential to eliminate the metal-to-metal contact/boundary friction that exists close to the piston reversal areas. This frictional source becomes a significant energy loss, especially in the compression/expansion part of the cycle, when the gas pressure that loads the piston rings and skirts is high. This paper describes the Diesel RLE prototype constructed from a Cummins 4BT and the preliminary observations from initial low load testing. The critical technical challenge, namely the rotating liner face seal, appears to be operating with negligible gas leakage and within the hydrodynamic lubrication regime for the loads tested (peak cylinder pressures of the order of 100 bar) and up to about 10 bar BMEP (brake mean effective pressure). Preliminary testing has proven that the metal-to-metal contact in the piston assembly mostly vanished, and a friction reduction at idle conditions of about 40% as extrapolated to a complete engine has taken place. It is expected that as the speed increases, the friction reduction percentage will diminish, but as the load increases, the friction reduction will increase. The fuel economy benefit over the US Heavy-Duty driving cycle will likely be of the order of 10% compared to a standard engine.

Numerical Investigation and Multi-Objective Optimization of Internal EGR and Post-Injection Strategies on the Combustion, Emission and Performance of a Single Cylinder, Heavy-Duty Diesel Engine

This work presents a numerical study that investigates the optimum post-injection strategy and internal exhaust gas recirculation (iEGR) application with intake valve re-opening (2IVO) aiming to optimize the brake specific nitric oxide (bsNO) and brake specific soot (bsSoot) trade-off with reasonable brake specific fuel consumption (BSFC) via 1D engine cycle simulation. For model validation, single and post-injection test results obtained from a heavy-duty single cylinder diesel research engine were used. Then, the model was modified for 2IVO application. Following the simulations performed based on Latin hypercube DoE; BSFC, bsNO and bsSoot response surfaces trained by feedforward neural network were generated as a function of the injection (start of main injection, post-injection quantity, post-injection dwell time) and iEGR (2IVO dwell) parameters. After examining the effect of each parameter on pollutant emission and engine performance, multi-objective pareto optimization was performed to obtain pareto optimum solutions in the BSFC-bsNO-bsSoot space for 8.47 bar brake mean effective pressure (BMEP) load and 1500 rpm speed condition. The results show that iEGR and post-injection can significantly reduce NO and soot emissions, respectively. The soot oxidation capability of post-injection comes out only if it is not too close to the main injection and its efficiency and effective timing are substantially affected by iEGR rate and main injection timing. It could also be inferred that by the combination of iEGR and post-injection, NO and soot could be reduced simultaneously with a reasonable increase in BSFC if start of main injection is phased properly.

Combustion, criteria pollutant and soot property assessment of mixing-controlled high-load engine operation with gasoline and diesel

Gasoline compression ignition (GCI) is an emerging technology that can achieve high fuel efficiency and low criteria emissions in diesel engine platforms using gasoline and gasoline-like fuels. While low- and mid-range loads are enabled with low temperature combustion (LTC) approaches, high-loads are more efficient with high temperature combustion (HTC) requiring mixing-controlled combustion (MCC). Lower soot emissions are achieved with gasoline even in high-load MCC than with diesel, but detailed soot properties from gasoline and diesel have been rarely discussed. In order to better understand how high-load operations affect soot properties, gasoline and diesel were tested in a six-cylinder heavy duty engine at 14 bar brake mean effective pressure (BMEP) at similar combustion phasing. Effects of pilot mass ratio and EGR on heat release rates, cylinder temperatures, ignition delay (ID) and combustion duration (CD) were examined, relating with emissions variations with applications of the two fuels. Soot mass and particle number emissions were slightly lower with gasoline than with diesel, resulting in a more favorable NOx-soot trade-off with gasoline like other reports. Contrary to other findings in the literature, gasoline and diesel soot samples presented similar particle distribution shapes, carbon crystalline structures and primary particle sizes, regardless of fuel type and EGR rate. Consequently, the current result proposes that soot particles have undergone similar soot formation and oxidation processes despite reactivity difference and oxygen availability under the examined high-load MCC with similar combustion phases.

Development and comparative experimental investigations of laser plasma and spark plasma ignited hydrogen enriched compressed natural gas fueled engine

A customized port-fuel-injection (PFI) SI engine was operated in spark ignition (SI) and laser ignition (LI) modes at varying brake mean effective pressure (BMEP) and relative air-fuel ratio (λ) under naturally aspirated conditions. Test fuel used were hydrogen enriched compressed natural gas (HCNG) mixtures and results were compared with baseline CNG. For H2 enrichment of CNG, a customized dynamic fuel mixing system was developed. For LI, a solid state Q-switched Nd:YAG laser (200 mJ; 30 Hz; 6–9 ns) was used, and the laser beam was focused using a converging lens of 50 mm focal length. Experiments of HCNG fueling exhibited relatively higher peak pressure (Pmax) with its peak shifted closer to the top dead center (TDC). H2 enrichment of CNG led to increase in peak in-cylinder Pmax (by ∼2.9 bar), RoPR (by ∼0.72 bar/deg) and HRR (by ∼7.2 kJ/m3.deg) for 40HCNG compared to baseline CNG. The maximum BTE was observed to be ∼42.8% (at λ = 1.4) in LI mode for 30HCNG fueled engine. The lowest BSFC obtained were at λ = 1.2 for HCNG in SI mode, while corresponding value in LI mode was obtained at λ = 1.4. BSHC emissions were always lower for LI mode than the SI mode. At 3.96 bar BMEP, BSHC emissions reduced from 0.54 g/kWh (for CNG) to 0.35 g/kWh (for 40HCNG), which further reduced to 0.21 g/kWh (for H2) in LI mode. BSNOx emissions increased with increasing BMEP but reduced from 0.89 g/kWh at λ = 1.5 for CNG to 0.17 g/kWh for 30HCNG at λ = 1.7 at 30 Nm load.

A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines

AbstractDual-fuel diesel–methane low-temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen oxide (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual-fuel LTC typically exhibits poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting CO and UHC oxidation once combustion is initiated by the first one. In this study, diesel–methane dual-fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas (NG) surrogate). A multidimensional model is first validated in comparison with the experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 crank angle degrees (CAD) and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion and emissions are investigated, again showing good agreement with the experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline still remaining at very low level (under 1 g/kWh). Furthermore, it is shown that postinjection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.