Variation Of Indicated Mean Effective Pressure Research Articles

Investigation of In-Cylinder Pressure Measurement Methods within a Two-Stroke Spark Ignition Engine

<div>This work describes an investigation of measurement techniques for the indicated mean effective pressure (IMEP) on a 55 cc single-cylinder, 4.4 kW, two-stroke, spark ignition (SI) engine intended for use on Group 1 and Group 2 remotely piloted aircraft (RPAs). Three different sensors were used: two piezoelectric pressure transducers (one flush mount and one measuring spark plug) for measuring in-cylinder pressure and one capacitive sensor for determining the top dead center (TDC) position of the piston. The effort consisted of three objectives: to investigate the merits of a flush mount pressure transducer compared to a pressure transducer integrated into the spark plug, to perform a parametric analysis to characterize the effect of the variability in the engine test bench controls on the IMEP, and to determine the thermodynamic loss angle for the engine. The results indicate that as a spark plug, the measuring spark plug is not statistically different from the stock spark plug at the 95% confidence level. The results indicate a statistically significant, 4% difference in the measured IMEP between the pressure transducer in the measuring spark plug and the flush mount transducer. The results also suggest a statistically significant difference in performance between the modified and unmodified engine heads, verifying the suppositions of other researchers who suggested that even a small modification to a combustion chamber this size could measurably affect the engine performance. While run-to-run variation resulted in a 2% to 5% variation in IMEP, a sensitivity analysis determined that 1% to 3% of that variation arose from variability in the control variables, while the remainder was caused by variation in other engine operating parameters. Between 1000 rpm and 2000 rpm, where the engine was typically motored to determine the TDC, the thermodynamic loss angle was 0.3 crank angle degrees (CAD) to 0.7 CAD, larger than loss angles observed in automotive-sized gasoline engines. The results indicate that using tabulated thermodynamic loss angles to set the TDC location of the engine using a mono-directional peak pressure method would lead to a −1% to −2.5% bias in the IMEP.</div>

Research on combustion and emission characteristics of a hydrous ethanol/hydrogen combined injection spark ignition engine under lean-burn conditions

Ethanol, as one of the carbon-neutral fuels for spark ignition (SI) engine, has been widely used. Dehydration and purification of ethanol during production process will lead to high energy consumption. If hydrous ethanol can be directly applied to the engine, the cost of use will be greatly reduced. Due to the high latent heat of vaporization of ethanol and water, it is necessary to consider the performance of atomization, evaporation and combustion stability when hydrous ethanol is used in engine. As a zero-carbon fuel, hydrogen has excellent characteristics such as low ignition energy, fast flame propagation speed and wide combustion limit. The combination of hydrous ethanol and hydrogen can reduce the use cost and ensure better combustion performance. Therefore, this study explores the performance of hydrous ethanol/hydrogen in SI combined injection engine. The hydrous ethanol is injected into the intake port and the hydrogen is directly injected into the cylinder during the compression stroke. In this study, we firstly analyze the optimal water blending ratio (ω) of hydrous ethanol, which including 0, 3%, 6%, 9% and 12%. The experimental results show that the hydrous ethanol with 9% water ratio has the best performance without hydrogen addition. Based on the 9% water ratio, the effects of hydrogen blending ratio (0, 5%, 10%, 15% and 20%) on the combustion and emission under different excess air ratio (λ) (1, 1.1, 1.2, 1.3, 1.4). Hydrogen addition can increase the degree of constant volume combustion, so that the maximum cylinder pressure and temperature increase with the increase of the hydrogen blending ratio (HBR). When λ = 1.3 and HBR = 20%, the maximum in-cylinder pressure can be increased by 108.64% compared to pure hydrous ethanol. Hydrogen effectively increases the indicated mean effective pressure (IMEP) and reduces the coefficient of variation of IMEP (COVIMEP). Adding hydrogen can reduce CO and HC emissions, while NOx emissions will increase. When λ = 1.2 and HBR increasing from 0 to 20%, the NOx emissions increase by 106.75%, but it is still less than the NOx emissions of pure hydrous ethanol at λ = 1. On the whole, hydrogen direct injection can improve the combustion performance of hydrous ethanol and achieve stable combustion under lean-burn conditions.

Experimental study on cycle-to-cycle variations in natural gas/methanol bi-fueled engine under excess air/fuel ratio at 1.6

In this study, the cycle-to-cycle variations in natural gas/methanol bi-fueled engines under excess air/fuel ratio at 1.6 was analyzed. In order to examine the impact of the methanol substitution ratio (MSR) on cyclic variability, four values of MSRs (MSR = 0%, 3.6%, 7.5%, and 11.5%) were selected under low load conditions. The results showed that the variations in the multicycle in-cylinder pressure traces decreased with the increase in MSR. In addition, the variations in peak in-cylinder pressure (Pmax), peak of pressure rise rate (dp/dϕ)max, 50% mass fraction burned (CA50), peak of averaged gas temperature (Tmax), and indicated mean effective pressure (IMEP) in 100 consecutive cycles decreased with the increase in MSR. Meanwhile, the higher was the MSR, the narrower was the range of frequency distribution of Pmax, (dp/dϕ)max, CA50, Tmax, and IMEP covered. In addition, the coefficient of variation in IMEP (COVIMEP) decreased with the increase in MSR for a specific spark timing. For instance, as MSR increased from 0% to 11.5%, the value of COVIMEP decreased from 2.25% to 1.28% when the spark timing was set to 46°CA BTDC. This is because methanol addition to natural gas leads to faster combustion with less cyclic variability.

Detailed analysis of combustion stability in a spark-assisted compression ignition engine under nearly stoichiometric and heavy EGR conditions

Extending the load range of low-temperature combustion is of priority to meet future CO2 and emission targets for reciprocating engine applications. Spark assist is a feasible solution to this challenge for mono-fuel homogeneous charge compression ignition (HCCI). This paper explains how spark-assisted compression ignition (SACI) enables ultra-low NOX targets to be met, with acceptable pressure rise rates and combustion stability, at high load boundary conditions, favourable for HCCI/SACI transition. The work provides new methods of combustion analysis which give better understanding of the mechanisms and their implementation for real-time control of SACI engines. The goals are achieved by a combination of single-cylinder engine research and high-fidelity/high-speed, model-based calculations, performed on an individual cycle basis. The results show that determining the start of the kinetic phase in SACI is possible via standard combustion indicators. The new method is two orders of magnitude faster than the commonly used spline-Wiebe approach. With real-time capability and proven correlation to temperature evolution, triggered by propagating flame, the method enables in-cycle predictive control. Additionally, it gives a deeper insight of the mechanisms underpinning the demonstrated superior performance. The study shows the capability to run SACI at indicated mean effective pressure (IMEP) of 0.5 MPa with engine-out NOX below Euro VI’s heavy-duty engine limit and with specific fuel consumption of 207 g/kWh. Importantly, pressure rise rate and variation in IMEP do not exceed 0.25 MPa/CAD and 3% respectively. Margins for critical parameters are far greater than for baseline autonomous HCCI, providing significant load extension potential.

An experimental investigation on combustion and performance characteristics of supercharged HCCI operation in low compression ratio engine setting

This study investigates the effects of boost pressure on combustion and performance of an early direct injection homogenous charge compression ignition (HCCI) engine at a low compression ratio (CR). A 2.0 L, four-cylinder, four-stroke, gasoline direct injection engine was converted to operate in early direct injection HCCI mode. In addition, a supercharger unit was developed for engine boosting. The experiments were performed at different intake manifold absolute pressures (MAP) from 1.0 to 1.6 bar at different engine loads using n-heptane fuel. The effects of boost pressure were investigated on HCCI combustion and engine performance characteristics using volumetric efficiency, in-cylinder pressure, heat release rate (HRR), maximum in-cylinder pressure and gas temperature, CA50 (crank angle by which 50% of the fuel is burnt), combustion duration, apparent combustion efficiency, indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP), friction mean effective pressure (FMEP), indicated thermal efficiency (ITE), brake thermal efficiency (BTE), heat loss, exergy of heat loss, coefficient of variation of IMEP (COVIMEP), maximum pressure rise rate (MPRR) and ringing intensity (RI). The experimental results showed that high-efficiency HCCI operation is feasible at an engine compression ratio as low as 9.2 once the engine variables are properly optimized and an appropriate level of supercharging is utilized. An increase in indicated thermal efficiency was seen as boost pressure increased. In addition, combustion phasing advanced by increasing boost pressure or increasing air–fuel equivalence ratio values. Combustion events with CA50 2–3 °CA aTDC show the highest thermal efficiency especially at low boost pressure conditions. In addition, the pressure rise rate and ringing intensity increased by increasing air–fuel equivalence ratio and MAP. The test results also showed that HCCI operating range can be extended with the increase of intake manifold pressure especially at high load limits.

Influence of water port injection on cycle-to-cycle variations in heavy-duty natural gas engine under low load

Water injection is regarded as an effective approach to decrease thermal load and suppress knock onset in heavy-duty natural gas engines. However, the cycle-to-cycle variations in heavy-duty natural gas engines via water injection has rarely been investigated. In this study, the effects of water port injection on cycle-to-cycle variations in a natural gas engine were analyzed experimentally. The engine speed was fixed at 1600 r/min, and engine load was set at a low load with a brake mean effective pressure of 0.387 MPa. Three excess air-fuel ratios (λ = 1.0, 1.2, and 1.4) were defined; and four water to natural gas mass ratios (WNMRs) were set. The results demonstrated that the variations of multicycle cylinder pressure traces consistently increased with the increase in WNMR. The interdependence between the peak in-cylinder pressure (Pmax) and its corresponding crank angle became more dispersed, and the frequency distribution of Pmax covered a wider range with increasing WNMR. The obvious fluctuations and wide range of distribution of indicated mean effective pressure (IMEP) were determined by water addition. The higher the λ, the larger the fluctuations and wider the range of distribution of IMEP. The coefficient of variation of IMEP (COVIMEP) increased with the increase in WNMR and λ. However, the maximum COVIMEP among the three λs and four WNMRs did not exceed 3%. Thus, it can be concluded that no drivability problem is associated with water injection under low load.

Research on the combustion and emissions of an SI engine with acetone-butanol-ethanol (ABE) port injection plus gasoline direct injection

Recently, more attention has been paid to the application of biobutanol in spark ignition (SI) engines due to its superior properties among the biofuels. However, the high energy consumption and low efficiency of recovering biobutanol from ABE solution during the fermentation process lead to the high price of biobutanol, which limits its popularization in vehicles. Using ABE directly can solve the problem of high price of bio-butanol. This research explored the performance of an SI engine with ABE port injection (ABEPI) plus gasoline direct injection (GDI) at different excess air ratio (λ = 0.9, 1.0, 1.1, 1.2) and ABE port injection ratio (ABEPIr = 0, 25%, 50%, 75%, 100%). The results show that CA10-90 declines with increasing ABEPIr. CA0-10 and CA0-90 decrease with ABEPIr increasing at λ = 0.9, and first descend and then rise at λ = 1.0, 1.1 and 1.2. The coefficient of variations of IMEP (CoVIMEP) reaches the minimum value at ABEPIr = 75%. As ABEPIr increases, the peak in-cylinder pressure (Pmax), indicated mean effective pressure (IMEP) and brake thermal efficiency (BTE) increase at λ = 0.9 while first increase and then decrease at λ = 1.0, 1.1 and 1.2, reaching the maximum values at ABEPIr = 75%. Hydrocarbon (HC) reaches the minimum value at ABEPIr = 50%. Particle number decreases dramatically as ABEPIr increases from 0% to 50% and remains at an extremely low level when ABEPIr is greater than 50%. In summary, ABE is suitable for SI engine as an alternative fuel and fuels with high ABE ratio (≥50%) can effectively improve the combustion and particle emissions by ABEPI + GDI combined injection.

Comparative study of combustion process and cycle-by-cycle variations of spark-ignition engine fueled with pure methanol, ethanol, and n-butanol at various air–fuel ratios

The combustion characteristics and cycle-by-cycle variations of a spark-ignition engine fueled with pure methanol, ethanol, and n-butanol were comparatively analyzed. All experiments were performed using a natural gas/alcohols dual-fuel engine with the alcohol fuel energy substitution ratio of 100%. The engine was kept under a low load with a brake mean effective pressure of 0.387 MPa. Engine speed was kept constant at 1600 r/min and air–fuel ratio (λ) was set in the range of 1–1.5 and varied in intervals of 0.1. The results showed that the pure methanol fuel yielded the highest peak cylinder pressure (Pmax) and peak heat-release rate (HRRmax) of the engine, followed by ethanol and then n-butanol. Moreover, Pmax and HRRmax decreased with the increase in λ, and the corresponding crank angles were reduced for the three primary alcohol fuels. The flame-development and flame-propagation periods of methanol were shorter than those of ethanol and n-butanol. The indicated mean effective pressure (IMEP) was distributed in a wider range with the increase in λ for the engine fueled with ethanol and n-butanol. However, for methanol, the IMEP was distributed in a relatively narrow range under all conditions of λ. When λ was increased from 1.0 to 1.5, the coefficient of variation in IMEP (COVIMEP) of methanol increased from 1.36% to 2.65%, the COVIMEP of ethanol increased from 1.71% to 10.46%, and the COVIMEP of n-butanol increased from 2.06% to 15.66%. Thus, methanol had a higher burning rate, lower cycle-by-cycle variations, and a better lean-burn capability than that of ethanol and n-butanol.

Cycle by cycle variations of LPG-gasoline dual fuel on a multi-cylinder MPFI gasoline engine

ABSTRACTCombustion stability of a multipoint port fuel injection spark ignition engine working on liquefied petroleum gas (LPG)-gasoline dual fuel mode of operation was analysed. LPG-gasoline ratio was varied from 0 to 100% by controlling the injector signals at wide open throttle condition and 3000 RPM. Increasing LPG ratio will give higher peak pressure and higher indicated mean effective pressure (IMEP) because of the higher flame propagation speed of LPG. The experiment showed that maximum pressure will occur nearer to top dead centre when compared to gasoline. Fluctuation in maximum pressure is higher for LPG and is minimum for 50% LPG. Time return map showed that combustion instabilibity will be more for 100% LPG and is less for 50% LPG. Coefficient of variation of IMEP and maximum pressure for gasoline is higher than LPG. With 100% LPG, NOx emission is almost three times that of gasoline. Hence it can be concluded that 50% LPG will give the better combustion characteristics when compared to other fuel blends.

Experimental and numerical investigations on the cyclic variability of an ethanol/diesel dual-fuel engine

Experiments and simulations were used to explore the cyclic variability of an ethanol/diesel dual-fuel engine. The experiments were conducted on a light-duty diesel engine fueled with port injection of ethanol and direct injection of diesel. The influences of engine load, ethanol proportion and diesel injection timing on the cyclic variability were investigated. In-cylinder pressure traces of 150 consecutive cycles were acquired at each test condition. Consequently, cyclic variations of ignition timing (CA5), combustion phasing (CA50), accumulated heat release (Qf) and indicated mean effective pressure (IMEP) were used to quantify the cyclic variability. The experimental results showed that the fluctuations of CA5 and CA50 were very small throughout the premixed ratio sweep for both the light and high loads. However, the cyclic variation of IMEP was increased with the increasing ethanol ratio at both load conditions. And the cyclic variation of IMEP was reduced at the high load. The variations of IMEP and Qf showed similar magnitudes and trends at the test conditions, indicating that the cyclic variation of IMEP was mainly caused by the variation of Qf. Simulations confirmed that the combustion of premixed ethanol showed larger variations to initial in-cylinder temperature fluctuations at the light load, and consequently resulted in higher cyclic variation of Qf. At the high load, the increased combustion temperature enhanced the oxidation of ethanol, which contributed to stabilizing the combustion and reducing the cyclic variations. The cyclic variations increased with retarded diesel injection timing, which was mainly due to the reduced combustion temperature.

Spark-ignited engine NOx emissions in a low-nitrogen oxycombustion environment

This paper investigates the formation of the pollutant nitric oxides (NOx) in the low-nitrogen (N2) environment of methane oxycombustion in a spark-ignited (SI) internal combustion engine. Working fluid composition, N2 concentration, O2 concentration, compression ratio (CR) and spark-timing have been investigated to evaluate the feasibility of operating such a system below NOx regulation levels without after-treatment systems.NOx emissions in g/kWh are shown under equivalent CR, intake temperature, and indicated mean effective pressure (IMEP) at maximum brake torque spark-timing, to have an approximately linear dependence on N2 concentration from no N2 to normal air combustion. At a given N2 concentration, NOx emissions were found to be adversely correlated with power, thermal efficiency, and the coefficient of variation of IMEP. It was found that with 2–3% N2 by volume in the working fluid, it was possible to reduce NOx emissions to satisfy regulation levels, but this corresponds to non-ideal engine performance in other metrics. Satisfying regulations while operating at the maximum thermal efficiency required the N2 concentration be reduced to 1–2% by volume.The system was simulated using an AVL Boost model, with results indicating that the increasing NOx concentrations at higher O2 cases and earlier spark-timings can largely be attributed to higher burned-gas temperatures. An additional simulation utilizing CHEMKIN and the GRI 3.0 mechanism was used to estimate NOx formation, and with results indicating that air-calibrated NOx mechanisms maintain reasonable accuracy in low-N2 environments.

Investigation of cyclic variations of IMEP under idling operation in spark ignition engines

Cyclic variability limits the range of operating conditions of spark ignition engines, especially under lean and highly diluted operation conditions. The cyclic combustion variations can be characterized by pressure parameters, combustion related parameters, and flame-front related parameters. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle.

火花点火機関の希薄燃焼運転時における図示平均有効圧力の変動

In this study, we investigated the relationship of indicated mean effective pressure (IMEP) for a spark ignition engine under lean combustion with the cyclic variation of mass fraction burned by measuring the energy release from the spark plug, inteasity of the light emission from the flame and the cylinder oressure at the same time. In orde _o minimized an error in the initial and late combustion s ages of the mass fraction burned to be obtained by cylinder pressure, spark plug energy and intensity of light emission were measured. As a result, it was found that there are three main causes of cyclic variation of IMEP. These consist of the burning speed during the initial stage of combustion, variation in the total mass fraction burned, and variation of the late burning during the late expansion stroke. Thus, we determined that there is a favorable interrelationship between the IMEPs and the corrected mass fraction burned.

Comparison of Lean Combustion Behavior of Conventional Gasoline and Alternative Fuels for S.I. Engine.

An SI engine test was carried out to elucidate the effect of fuel properties on the engine performance in a lean combustion region. Several combustion characteristics, i. e., the indicated mean effective pressure (IMEP), the cycle variation of IMEP, the combustion duration, the fuel consumption and the indicated thermal efficiency, were demonstrated for four kinds of alternative fuels and regular gasoline with equivalence ratio ranging from 0.56 to 1.0. From the results of this test, we have cofirmed that the fuel composition significantly affected engine combustion under lean-burn conditions. This study has also revealed the effect of fuel properties on exhaust emissions, such as the carbon monoxide (CO), the total hydrocarbon (THC) and the nitrogen oxide (NOx) amount. The CO emissions did not depend on the fuel types, but the THC emissions and the NOx emissions were affected by differences between several fuel types in the lean region. In an extremely lean region, however, the NOx emissions became similar for all fuels.