Bar Indicated Mean Effective Pressure Research Articles

Experimental investigation of the control strategy of high load extension under iso-butanol/biodiesel dual-fuel intelligent charge compression ignition (ICCI) mode

Advanced combustion modes have shown the great advantages to achieve high thermal efficiency and low pollution emissions. However, lack of sufficiently control over combustion phasing of heat release under high and ultra-high engine load limits the commercial application. In this paper, an experimental investigation had been conducted to explore the control strategy under iso-butanol/biodiesel dual-fuel intelligent charge compression ignition (ICCI) mode for achieving the high engine load extension. The criteria is used to identify clean combustion under high load expansion, which the indicated thermal efficiency is 45% or higher, and nitrogen oxides (NOx) emissions should be below 400 ppm. The results show that stable and controllable ICCI operation is obtained under high and ultra-high engine load. An iso-butanol single direct injection in the intake stroke, biodiesel double direct injection strategy in the compression stroke and near top dead center, respectively, offers a very competitive pathway to expand the engine load with clean and highly efficient combustion, in which the maximum indicated thermal efficiency reaches 49.9% and NOx emissions below 100 ppm at the indicated mean effective pressure (IMEP) of 12 bar, and the maximum engine load reaches 18 bar IMEP (96% engine load). At higher engine load, lower iso-butanol energy ratio is used to reduce the in-cylinder pressure and maximum pressure rise rate, while punishes the engine thermal efficiency and emissions. With the iso-butanol energy ratio increase, the lower in-cylinder reactivity leads to the increase of incomplete combustion products. In addition, the exhaust gas recirculation (EGR) is essential on the reduction of NOx emissions, and the second biodiesel injection duration is increased with the engine load increase for the purpose of the load expansion.

Effects of low-carbon high-reactivity fuels on combustion and emission characteristics in a part-load condition of a DICI engine

Diesel engines face a challenge on environment pollutions, especially nitrogen oxides (NOx) and particle emissions. In recent years, advanced combustion modes were developed and fuels for different physical and chemical performances were investigated. Many researches showed that naphtha fuels well suited for compression ignition engines. In this paper, two reformates from naphtha fuels, named as High Reactivity Gasoline (HRG) and High Reactivity Gasoline blended with ethanol (HRE), and diesel were used to learn the effects on combustion and emissions of a single-cylinder compression-ignition (CI) engine. Experiments were conducted at a low load operating point, 1055 r/min-7.2 bar IMEP (gross indicated mean effective pressure) which could significantly show the effects of different fuels’ characteristics. A dual split fuel injection strategy was employed. In the experimental condition, fuel injection pressure, intake pressure, and exhaust gas recirculation (EGR) rate were maintained the same for all test fuels. Horiba MEXA-7200 and DMS500 were used to measure gas emissions and particle number (PN) emissions respectively. Results showed that HRG and HRE realized a stable combustion on diesel engine by using a two-stage injection strategy. HRE had the longest ignition delay leading to a single-stage heat release rate which was different from that with the other fuels. As a result, the trends of combustion and emission characteristics were unique. For HRE, the second injection timing (SOI2) dominated the maximum cylinder pressure rise rate (PRMAX) while it showed little effect on PRMAX using the other fuels. Fuel with low chemical reactivity could reduce the NOx emission and led to high CO and THC emissions. However, HRE had an overlong ignition delay led to an overlap of two combustion stages. The combustion was fast and the NOx emission became worse. In the experimental condition, the nucleation mode particles dominate the PN emissions. HRE and diesel had huge nucleation mode particle emissions due to the short combustion duration and the enhanced diffusion combustion, respectively. In conclusion, HRG had advantages on emissions which showed the lowest PRMAX, NOx and PN emissions and HRE had the advantage on engine working efficiency which could reach 47.8% in this study.

High efficiency ethanol–diesel dual-fuel combustion: Analyses of performance, emissions and thermal efficiency over the engine load range

The performance of ethanol–diesel dual-fuel combustion is evaluated against that of the conventional diesel high-temperature combustion (HTC) from 4 bar (low engine load) to 19 bar net indicated mean effective pressure (IMEP) at 1500 rpm on a single cylinder high-compression ratio diesel engine. Ethanol is injected into the intake port, along with direct injection of diesel fuel. For both combustion strategies, engine operation is optimized by modulating the intake pressure, exhaust gas recirculation (EGR) rate, ethanol energy fraction and diesel injection pressure to achieve the desired combustion performance, along with detailed feed-gas analysis to evaluate the trade-offs between combustion efficiency, NOx and PM. From 6 to 19 bar IMEP, the dual-fuel combustion results in 84 ∼ 88% lower NOx and 20 ∼ 96% lower soot emissions compared to diesel HTC, and at loads > 10 bar IMEP, attains higher net indicated efficiency than diesel HTC, with a maximum value of 46% at 19 bar IMEP. To ascertain the impact of NOx selective catalytic reduction system (SCR) on the net indicated thermal efficiency, SCR urea dosing penalties are evaluated using actual feed-gas NOx data with a simple SCR correlation for estimating the tail-pipe NOx emissions and urea consumption. To achieve 0.2 g/kWh for tail-pipe NOx, the diesel HTC requires ∼ 90% SCR conversion efficiency below 6 bar IMEP but at higher loads, the dual-fuel combustion requires a SCR efficiency of 20 to 50% only, with reduced urea consumption, and net efficiency higher than the diesel HTC. Using renewable bio-fuels such as ethanol, dual-fuel combustion can be an effective strategy to reduce the dependence on fossil fuels, reduce GHG emissions and improve the viability of diesel engines as a preferred choice for heavy-duty transport applications.

A Numerical Study to Control the Combustion Performance of a Syngas-Fueled HCCI Engine at Medium and High Loads Using Different Piston Bowl Geometry and Exhaust Gas Recirculation

Abstract This study aims to analyze the effect of piston bowl geometry on the combustion and emission performance of the syngas-fueled homogenous charge compression ignition (HCCI) engine, which operates under lean air–fuel mixture conditions for power plant usage. Three different piston bowl geometries were used with a reduction of piston bowl depth and squish area ratio of the baseline piston bowl with the same compression ratio of 17.1. Additionally, exhaust gas recirculation (EGR) is used to control the maximum pressure rise rate (MPRR) of syngas-fueled HCCI engines. To simulate the combustion process at medium load (5 bar indicated mean effective pressure (IMEP)) and high loads of (8 and 10 bar IMEP), ansys forte cfd package was used, and the calculated results were compared with Aceves et al.’s Multi-zone HCCI model, using the same chemical kinetics set (Gri-Mech 3.0). All calculations were accomplished at maximum brake torque (MBT) conditions, by sweeping the air–fuel mixture temperature at the inlet valve close (TIVC). This study reveals that the TIVC of the air–fuel mixture and the heat loss rate through the wall are the main factors that influence combustion phasing by changing the piston bowl geometry. It also finds that although pistons B and C give high thermal efficiency, they cannot be used for the combustion process, due to the very high MPRR and NOx emissions. Even though the baseline piston shows high MPRR (23 bar/degree), it is reduced, and reveals an acceptable range of 10–12 bar/degree, using 30% EGR.

A Numerical Study to Investigate the Effect of Syngas Composition and Compression Ratio on the Combustion and Emission Characteristics of a Syngas-Fueled HCCI Engine

Abstract The purpose of this work is to investigate syngas composition (of constituents H2, CO, and CO2) and compression ratio (CR) effects on the combustion and emissions characteristics of a syngas-fueled homogenous charge compression ignition (HCCI) engine, which operates in very lean air–fuel mixture conditions for power plant usage. Investigations were conducted using ansys forte cfd package at low (3 bar indicated mean effective pressure (IMEP)) and medium (5 bar IMEP) loads, and the calculated results were compared with the Aceves et al.’s multi-zone HCCI model, using the same chemical kinetics set (Gas Research Institute (GRI)-Mech3.0). All calculations were carried out at maximum brake torque (MBT) conditions by sweeping the air–fuel mixture temperature at intake valve closing (IVC) (TIVC).This study found out that the H2 consumption rate is slightly high in a low-temperature range in the early period of combustion while the CO consumption rate is high in a high-temperature range in the later period of combustion. The results reveal that the change of H2 /CO ratio and inert gas volume fraction according to fuel composition affects combustion, but the TIVC is the dominant factor affecting combustion phasing at MBT conditions. For each fuel and load condition, the TIVC was significantly reduced with the increase of CR (17.1–22.3) to get MBT conditions, which causes to retard combustion phasing and lowers in-cylinder peak temperature. The oxides of nitrogen (NOx) emissions reduced with increasing the CR due to the lowering of the in-cylinder peak temperature.

An Experimental Investigation on the Influence of Port Injection at Valve on Combustion and Emission Characteristics of B5/Biogas RCCI Engine

High unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions, on account of the premixed air-fuel mixture entering the crevices and pre-mature combustion, are setbacks to reactivity-controlled compression ignition (RCCI) combustion at a low load. The influence of direct-injected B5 and port injection of biogas at the intake valve was, experimentally, examined in the RCCI mode. The port injection at the valve was to elevate the temperature at low load and eliminate premixing for reduced pre-mature combustion and fuel entering the crevices. An advanced injection timing of 21° crank angle before top dead centre and fraction of 50% each of the fuels, were maintained at speeds of 1600, 1800 and 2000 rpm and varied the load from 4.5 to 6.5 bar indicated mean effective pressure (IMEP). The result shows slow combustion as the load increases with the highest indicated thermal efficiency of 36.33% at 5.5 bar IMEP. The carbon dioxide and nitrogen oxides emissions increased, but UHC emission decreased, significantly, as the load increases. However, CO emission rose from 4.5 to 5.5 bar IMEP, then reduced as the load increases. The use of these fuels and biogas injection at the valve were capable of averagely reducing the persistent challenge of the CO and UHC emissions, by 20.33% and 10% respectively, compared to the conventional premixed mode.

Investigation of Effects of Intake Temperature on Low Load Limitations of Methanol Partially Premixed Combustion

Methanol has unique properties as a fuel, and partially premixed combustion has promising results with high engine efficiency and low emissions. Low load studies with methanol partially premixed combustion are scarce, and the effect of intake temperature on low load methanol partially premixed combustion still remains an intriguing question. This study aims to investigate the effect of intake temperature on low load limitations of methanol partially premixed combustion by an experimental study. The engine was operated at 800 rpm under two different loads. The low load condition was performed at 3 bar Indicated mean effective pressure (IMEP), and the idle condition was commenced at 1 bar IMEP. From the results, it was seen that the intake temperature affected engine stability, engine performance, and engine emissions. The combustion stability decreased with the decrease of intake temperature. The ignition delay became longer and the peak cylinder pressure became smaller with lower intake temperature. The combustion efficiency reduced with the decrease of intake temperature from 0.99 to 0.96 at 3 bar IMEP, whereas it decreased from 0.99 to 0.98 at 1 bar IMEP for the single injection case and the split injection case. The thermodynamic efficiency remained constant at 0.43 at 3 bar IMEP, decreased from 0.30 to 0.28 at 1 bar IMEP for the single injection case, and reduced from 0.26 to 0.24 at 1 bar IMEP for the split injection case. The gross indicated efficiency increased from 0.41 to 0.42 at 3 bar IMEP, whereas it reduced from 0.29 to 0.28 and 0.26-0.24 at 1 bar IMEP at single injection and split injection, respectively. Total hydrocarbon emission increased, NOX emission decreased or remained constant, and CO emission remained constant with the decrease in intake temperature. Finally, the combustion phasing study was performed at 1 bar IMEP at constant intake temperature to determine the effect of the start of injection timing on the engine's performance and the emissions under the idle condition.

Experimental study of using additive in the pilot fuel on the performance and emission trade-offs in the diesel/CNG (methane emulated) dual-fuel combustion mode

In this work, diesel-n-butanol blends as the pilot fuel were studied to explore the possibility of improving the performance and emissions in the dual-fuel combustion mode with CNG, and the trade-offs among NOx, THC and CO were also discussed. The pilot fuels including B0 (pure diesel), B10 (90% diesel/10% n-butanol) and B20 (80% diesel/20% n-butanol) were compared under two engine loads. The experiments were conducted by sweeping a wide pilot fuel start of injection (SOI) timings at two CNG substitution rates for each load. For 5 bar indicated mean effective pressure (IMEP), B10CNG40 (at the 40% CNG substitution rate) reveals the highest indicated thermal efficiency (ITE) and lowest THC emissions. While it results in slightly higher NOx emission. B20CNG70 can significantly reduce the NOx emission due to better homogeneity and higher evaporation latent heat of n-butanol. The obvious trade-offs between NOx and THC, NOx and CO can be observed at the retarded pilot fuel SOI timings. For 7.5 bar IMEP, B10CNG60 and B20CNG60 can improve ITE and lower the THC emissions, while maintaining the equivalent level of NOx emission relative to the cases at the 80% CNG substitution rate. Adding n-butanol leads to the trade-off between THC and CO emissions.

Experimental investigation into effects of high reactive fuel on combustion and emission characteristics of the Diesel - Natural gas Reactivity Controlled Compression Ignition engine

Reactivity Controlled Compression Ignition (RCCI) engines hold promise for decreasing NOx and particulate emissions. RCCI engines use direct injection (DI) to introduce a high reactivity fuel into the cylinder while a lower reactivity fuel is port fuel injected (PFI). A large reactivity difference between high reactive (diesel) and low reactive (natural gas) fuels provides a strong control variable for phasing and shaping combustion heat release in RCCI engines.Two diesel fuels, a High Reactive Diesel (HRD) fuel with a cetane number (CN) of 85 and a U.S. Ultra-Low Sulfur Diesel (ULSD) fuel with a cetane number of 49 were selected for this study. The effects of these two diesel fuels with methane as the low reactivity premixed fuel were compared in RCCI combustion mode and in Conventional Diesel Combustion (CDC) mode.The hypothesis is that using a HRD fuel in RCCI applications, with a double injection strategy, increases the reactivity of the mixture in the squish region, promoting combustion and consequently reducing unburned hydrocarbons and carbon monoxide. These emissions are generally difficult to control in RCCI combustion at high Blend Ratio (BR). In addition, a larger reactivity difference between the two fuels in RCCI applications, extends the combustion duration and reduces the Maximum Pressure Rise Rate (MPRR) and in-cylinder peak pressure. The reduction in MPRR in RCCI combustion mode makes it possible to operate the engine at higher engine loads without exceeding the MPRR mechanical constraint.The experiments were performed on a 1.9L inline 4 cylinder turbocharged compression ignition (CI) engine modified for dual fuel operation at an engine speed of 1500 RPM and 8 bar IMEP. A full factorial Design of Experiment (DOE) test program and analysis was conducted with four input variables including the diesel fuel reactivity, BR, Exhaust Gas Recirculation (EGR) and Direct Injection (DI) strategy and at two levels of interest. This analysis was used to quantify the impact of the independent input variables on engine out emissions, performance, and MPRR mechanical constraint. Following the DOE testing and analysis the optimum injection strategy to maximize the Brake Thermal Efficiency (BTE) was found for both fuels by sweeping the main Start of Injection timing (SOImain).The results of the DOE analysis showed that the cetane number is the most significant factor that effects HC and CO emissions. The experimental results showed that HRD fuel provides a 2% improvement in brake-thermal efficiency, a 14 g/kW.hr reduction in HC emissions, and 0.5% lower Coefficient of Variation (COV) of Indicated Mean Effective Pressure (IMEP) compared to the baseline diesel-NG RCCI combustion.

Optimization of performance and operational cost for a dual mode diesel-natural gas RCCI and diesel combustion engine

Diesel-NG fuel blends are increasingly being used in Reactivity Controlled Compression Ignition (RCCI) internal combustion engines due to high Brake Thermal Efficiency (BTE), low NOx and PM emissions. It also has few disadvantages such as high unburned Hydro Carbon (HC) and Carbon Monoxide (CO) emissions and relatively low Exhaust Gas Temperature (EGT). This study determines the optimum combustion mode between RCCI and Conventional Diesel Combustion (CDC) at different loads while meeting the Environmental Protection Agency (EPA) emission regulation. A Cost Function (CF) including Brake Specific Fuel Consumption (BSFC) and Brake Specific Urea Consumption (BSUC) is considered and minimized in this study. The optimization of input variables is done between 3 and 12 bar Indicated Mean Effective Pressure (IMEP) engine load. The study aims to calibrate the dual fuel diesel/NG RCCI engine to meet Tier 3 Bin 20 EPA standard, with or without after-treatment system, while minimizing the cost of operation.New parametric empirical models are developed and validated using experimental data from a light duty 1.9L inline 4 cylinder Compression Ignition (CI) engine as a function of independent input variables. All the experiments were conducted at Advanced Power System (APS) facility at Michigan Technological University. These models predict HC, CO, PM and NOx emissions, EGT and BSFC. These models are then used to predict new operating points to increase the population in the optimization process. The computed EGT is used to estimate the Selective Catalyst Reduction (SCR) and Diesel Oxidation Catalyst (DOC) efficiencies to assess the emission data with different input variables by considering the after-treatment system to see if they meet the tailpipe emission regulation. The optimization results recommend using Diesel/NG RCCI at 7 to 12 bar IMEP operating conditions and use CDC for below 7 bar IMEP operating condition.

Comparative study on the pumping losses between continuous variable valve lift (CVVL) engine and variable valve timing (VVT) engine

VVL and VVT are two common approaches to reduce engine pumping loss at part loads, however, the comparative study on their potentials and influence factors of pumping loss reduction is scarce. In this paper, the gas exchange processes of CVVL and VVT engines were investigated by bench testing. The mechanism and influence factors of pumping loss in the two types of engines were comparatively analyzed, the theoretic limitations of pumping loss in intake process were deduced and the suggestions to approach the theoretic minimum were proposed. The results show that the gross indicated mean effective pressure (IMEP) of engine is approximately proportional to cylinder pressure at bottom dead center (BDC) for both traditional throttle control strategy and early intake valve closing (EIVC) strategy. The difference of pumping losses between CVVL and VVT engines results from intake process. Due to the differences of intake modes, the CVVL engine has lower intake loss than VVT engine by nature. The pumping loss in intake process of CVVL engine is much closer to the theoretical minimum, and the BSFC of CVVL engine can be reduced by more than 20% at 2000 r/min and 2.3 bar IMEP by increasing the maximum lift of intake valve. All these have provided guidance for pumping loss reduction of gasoline engine.

Investigation of EGR Effect on Combustion and PM Emissions in a DISI Engine

Exhaust gas recirculation (EGR) is a well known technique for suppressing knock and reducing nitrous oxide (NOx) emissions in spark-ignition engines, and this technique is now receiving more attention because of the negative effect of EGR on engine particulate emissions. This paper investigates the effect of EGR on engine combustion (in-cylinder pressure and temperature, mass fraction burned (MFB), knock limited maximum brake torque (KLMBT) spark timing, net indicated specific fuel consumption (ISFCnet), exhaust gas temperature) and emissions (NOx, unburned hydrocarbon (HC), particulate matter (PM)) in a direct injection spark ignition (DISI) engine. The tests were carried out in a single-cylinder DISI research engine with engine loads between 5.5 and 8.5bar indicated mean effective pressure (IMEP) and various EGR ratios of up to 13%. The results show that by adding 12% EGR, the KLMBT spark timing could be advanced by 8 crank angle degrees (CAD) which resulted in a 4.1% fuel consumption reduction at 7.0bar IMEP. EGR addition generally increased the accumulation mode particles and reduced the nucleation mode particles.

High Load (21 Bar IMEP) Dual Fuel RCCI Combustion Using Dual Direct Injection

Dual-fuel reactivity controlled compression ignition (RCCI) combustion has shown high thermal efficiency and superior controllability with low NOx and soot emissions. However, as in other low temperature combustion (LTC) strategies, the combustion control using low exhaust gas recirculation (EGR) or a high compression ratio at high load conditions has been a challenge. The objective of this work was to examine the efficacy of using dual direct injectors for combustion phasing control of high load RCCI combustion. The present computational work demonstrates that 21 bar gross indicated mean effective pressure (IMEP) RCCI is achievable using dual direct injection. The simulations were done using the KIVA3V-Release 2 code with a discrete multicomponent fuel evaporation model, coupled with sparse analytical Jacobian solver for describing the chemistry of the two fuels (iso-octane and n-heptane). In order to identify an optimum injection strategy a nondominated sorting genetic algorithm II (NSGA II), which is a multiobjective genetic algorithm, was used. The goal of the optimization was to find injection timings and mass splits among the multiple injections that simultaneously minimize the six objectives: soot, nitrogen oxide (NOx), carbon monoxide (CO), unburned hydrocarbon (UHC), indicated specific fuel consumption (ISFC), and ringing intensity. The simulations were performed for a 2.44 liter, heavy-duty engine with a 15:1 compression ratio. The speed was 1800 rev/min and the intake valve closure (IVC) conditions were maintained at 3.42 bar, 90 °C, and 46% EGR. The resulting optimum condition has 12.6 bar/deg peak pressure rise rate, 158 bar maximum pressure, and 48.7% gross indicated thermal efficiency. The NOx, CO, and soot emissions are very low.

PFI (port fuel injection) of n-butanol and direct injection of biodiesel to attain LTC (low-temperature combustion) for low-emissions idling in a compression engine

In this study, n-butanol (port fuel injection) PFI was investigated in a direct injection compression ignition engine while at idling speeds, and loads, 1–3 bar IMEP (indicated mean effective pressure) in order to determine the effects on combustion, efficiency, emissions, and specifically, a modified tradeoff of soot and nitrogen oxides. As a result, the engine entered into (low-temperature combustion) LTC regions, for selected loads and speeds. Compared with the baseline taken with ultra-low sulfur diesel no. 2, the heat release with n-butanol in (premixed charge compression ignition) PCCI mode, has resulted in a 75% reduction from the maximum values, while a secondary peak appeared where the diffusion combustion typically occurs in the power stroke. At 3 bar IMEP an early, (bottom dead center) BTDC low-temperature heat release was found that began 6° earlier than for the diesel reference cycle, and corresponding to 1200 K. Soot emissions showed a massive decrease of about 98%, concurrently with a 74% reduction of nitrogen oxides at 3 IMEP by controlling the combustion phases and by modifying the classical NOx–soot tradeoff. The results of this work prove that biodiesel combined with n-butanol PFI in PCCI and LTC are very effective in simultaneously reducing soot and NOx at idling speeds.

Empirical Study of Simultaneously Low NOx and Soot Combustion With Diesel and Ethanol Fuels in Diesel Engine

Diesel low temperature combustion (LTC) is capable of producing diesel-like efficiency while emitting ultra-low nitrogen oxides (NOx) and soot emissions. Previous work indicates that well-controlled single-shot injection with exhaust gas recirculation (EGR) is an operative way of achieving diesel LTC from low to mid engine loads. However, as the engine load is increased, demanding intake boost and injection pressure are necessary to suppress high soot emissions during the transition to LTC. The use of volatile fuels such as ethanol is deemed capable of promoting the cylinder charge homogeneity, which helps to overcome the high soot challenge and, thus, potentially expand the engine LTC load range. In this work, LTC investigations were carried out on a high compression ratio (18.2:1) engine. Engine tests were first conducted with diesel and LTC operation at 8 bar indicated mean effective pressure (IMEP) was enabled by sophisticated control of the injection pressure, injection timing, intake boost, and EGR application. The engine performance was characterized as the baseline, and the challenges were identified. Further tests were aimed to improve the engine performance against these baseline results. Experiments were, hence, conducted on the same engine with secondary ethanol port fuelling (PF). Single-shot diesel direct injection (DI) was applied close to top dead center (TDC) to ignite the ethanol and control the combustion phasing. The control sensitivity was studied through injection timing sweeps and EGR sweeps. Additional tests were performed to investigate the ethanol-to-diesel ratio effects on the mixture reactivity and the engine emissions. Engine load was also raised to 16.4 bar IMEP while keeping the simultaneously low NOx and soot emissions. Significant improvement of engine control and emissions was achieved by the DI+PF strategy.

Reducing NOx Emissions from a Biodiesel-Fueled Engine by Use of Low-Temperature Combustion

Biodiesel is popularly discussed in many countries due to increased environmental awareness and the limited supply of petroleum. One of the main factors impacting general replacement of diesel by biodiesel is NOx (nitrogen oxides) emissions. Previous studies have shown higher NOx emissions relative to petroleum diesel in traditional direct-injection (DI) diesel engines. In this study, effects of injection timing and different biodiesel blends are studied for low load [2 bar IMEP (indicated mean effective pressure)] conditions. The results show that maximum heat release rate can be reduced by retarding fuel injection. Ignition and peak heat release rate are both delayed for fuels containing more biodiesel. Retarding the injection to post-TDC (top dead center) lowers the peak heat release and flattens the heat release curve. It is observed that low-temperature combustion effectively reduces NOx emissions because less thermal NOx is formed. Although biodiesel combustion produces more NOx for both conventional and late-injection strategies, with the latter leading to a low-temperature combustion mode, the levels of NOx of B20 (20 vol % soy biodiesel and 80 vol % European low-sulfur diesel), B50, and B100 all with post-TDC injection are 68.1%, 66.7%, and 64.4%, respectively, lower than pure European low-sulfur diesel in the conventional injection scenario.

New gasoline homogeneous charge compression ignition combustion system using two-state direct injection and assisted spark ignition

Homogeneous charge compression ignition (HCCI) combustion was studied in a four-stroke gasoline engine with a direct injection system. The spark ignition and electronically controlled two-stage gasoline injection system are adopted to control the mixture formation, ignition timing, and combustion rate in the HCCI engine. The engine could be operated in HCCI combustion mode in a range of loads from 1 to 5 bar indicated mean effective pressure (IMEP) and operated in SI combustion mode up to loads of 8 bar IMEP. The HCCI combustion characteristics were investigated under different air—fuel ratios, engine speeds, starts of injection, as well as spark ignition enabled or not. By introducing the second fuel injection in the compression stroke, the stratified concentration is formed and the mixture is cooled, which means that HCCI ignition timing can be controlled and the load range can be extended by tuning the mixture concentration and temperature. At a critical ignition temperature, especially in SI—HCCI combustion mode transition, assisted SI improves the stability of HCCI combustion. In order to understand better the physicochemical process in the cylinder, an improved three-dimensional computational fluid dynamics code has been utilized to simulate the intake, two-stage spray, compression, and combustion processes of the HCCI engine. The calculated results show that a homogeneous lean charge could be realized by single fuel injection in the intake stroke. With the help of the intake swirl and squish flow in the compression stroke, a rich mixture resulting from the second fuel injection can be formed near the spark. Hydroxyl ions (OH) reach to a maximum at the periphery of the fuel-rich zone; a great number of spots are ignited simultaneously. It works as an initiation to ignite the surrounding lean mixture zone.