Indicated Thermal Efficiency Research Articles

Effect of Excess Air Ratio on Idle Performance of a HCNG (H<sub>2</sub>+CNG) Engine with Different Hydrogen Blend Ratios

To investigate the idle performance of a HCNG with high hydrogen blend ratios, the effects of different excess air ratios (λ) and different hydrogen blend ratios on combustion, indicated thermal efficiency (ITE) and emissions of a 6-cylinder CNG engine were investigated. The results show that, with the increase of hydrogen blend ratio, rather high ITE can be achieved in a much wider range of λ. Under conditions of λ=1.2~1.4, emissions of CH4, NMHC and CO are relatively low for different hydrogen blend ratios. When the hydrogen blend ratio is greater than 75%, emissions of CH4, HMHC and CO increase only slightly with the increase of λ. NOx emissions increase with the increase of hydrogen blend ratio. And these emissions reach their peaks for different hydrogen blend ratios under the conditions of λ=1.1-1.2.

Effects of n-butanol, 2-butanol, and methyl octynoate addition to diesel fuel on combustion and emissions over a wide range of exhaust gas recirculation (EGR) rates

The effects of fuel properties and oxygenated structures on the combustion and emissions were investigated on a diesel engine. Five different fuels, n-heptane, iso-octane, n-butanol, 2-butanol and methyl octynoate, were added into diesel fuel with the same blending ratio (20% v/v), referred to as n-heptane20, iso-octane20, n-butanol20, 2-butanol20 and methyloctynoate20, respectively. A wide range of exhaust gas recirculation (EGR) rates from 0% to 62% were used to cover both the conventional diesel combustion and the low temperature combustion. Results demonstrate that there is little difference in combustion characteristics between n-heptane20 and the diesel fuel over a wide range of EGR rates. The ignition delay of iso-octane20 is retarded compared to that of n-heptane20 and the difference in ignition delay between iso-octane20 and n-heptane20 becomes larger with the increase of EGR rate. The combustion characteristics of n-butanol20 are similar to those of iso-octane20. The oxygen in n-butanol20 is the main factor for soot reduction in comparison with the diesel fuel. The secondary factor for soot reduction is the improvement in fuel mixing process due to the longer ignition delay caused by lower cetane number of n-butanol. Other changes in physical and chemical properties of n-butanol20 have very limited effect on soot reduction. Compared to methyloctynoate20, additional 12.6% reduction in the total soot emissions can be achieved by fueling n-butanol20 with the addition of 2-ethylhexyl nitrate (EHN), which can be attributed to the different molecular structures of the oxygenated fuels. The difference in locations of OH radical between n-butanol and 2-butanol has very small effect on soot emissions. The soot-reduction efficiency caused by fuel properties and oxygenated structures varies as the EGR rate changes. Fuel properties have little effects on NOx, CO, THC emissions and gross indicated thermal efficiency (ITE) under similar EGR conditions, while the EGR rates play a dominant role on the gaseous emissions and ITE.

A Highly Efficient Small-Displacement Marine Two-Stroke H2DI Engine With Low Emissions

A hydrogen-fueled two-stroke prototype demonstrator based on a 9.9 hp (7.4 kW) production gasoline marine outboard engine is presented, which, while matching the original engine's rated power output on hydrogen, achieves a best-point gross indicated thermal efficiency (ITE) of 42.4% at the ICOMIA mode 4 operating point, corresponding to 80% and 71.6% of the rated engine speed and torque, respectively. The brake thermal efficiency (BTE) at the rated power is 32.3%. Preliminary exhaust gas measurements suggest that the engine could also meet the most stringent CARB 5-Star marine spark-ignition emission standards limiting HC + NOx emissions to 2.5 g/kWh without any after-treatment. These are realized in a cost-effective concept around a proven two-stroke base engine and a low-pressure direct-injected gaseous hydrogen (LPDI GH2) system, which employs no additional fuel pump and is uniquely adapted from volume production components. Later fuel injection is found to improve thermal efficiency at the expense of increased NOx emissions and, at the extreme, increased cyclic variation. These observations are hypothesized and supported by phenomenological inferences of the observed trends of combustion duration, NOx concentration, and indicated mean effective pressure (IMEP) variance to be due to increasing charge stratification with the later timings. This work outlines the pathway—including investigations of several fuel delivery strategies with limited success—leading to the current status, including design, modeling with GT-POWER, delivery of lube oil, lubrication issues using hydrogen, and calibration sweeps. The experimental results comprising steady-state dynamometer performance, cylinder pressure traces, NOx emission measurements, along with heat release analyses, support the reported numbers and the key finding that late fuel injection timing and charge stratification drive the high efficiencies and the NOx trade-off; this is discussed and forms the basis for future work.

Experimental study of n-butanol addition on performance and emissions with diesel low temperature combustion

Compared with ethanol or methanol, butanol has higher heating value and higher miscibility. Because of lower cetane number of butanol, butanol-diesel blends are more suitable for diesel low temperature combustion (LTC). In the paper, experimental study was carried out on a modified single cylinder heavy duty diesel engine to investigate the effects of n-butanol and EGR on diesel engine's combustion and emission characteristics. CA50 timing was fixed at 8 °CA ATDC and two different volume fractions (20% and 40%) of n-butanol were blended into diesel fuel. The results showed that with the increase of n-butanol fraction, ignition delay prolonged, (dp/dφ)max increased and indicated thermal efficiency (ITE) had a slight increase. Fuel properties had little effects on NOx emission, but NO proportion decreased and NO2 proportion increased with higher n-butanol fraction. With n-butanol addition, CO and THC (total hydrocarbon) emissions decreased at higher EGR levels, soot emissions reduced greatly and soot-bump was almost eliminated. With the increase of EGR rate, CH4 proportion increased, but n-butanol addition could decrease CH4 proportion.

Performance and energy analyses of a diesel engine fuelled with Koroch seed oil methyl ester and its diesel fuel blends

Performance of a single cylinder four-stroke diesel engine is analysed in the light of first law of thermodynamics in this study considering 10% (B10) to 40% (B40) (by volume) blending of Koroch seed oil methyl ester (KSOME) with diesel as fuels. An energy balance study is carried out to quantify the various losses associated with diesel engine processes on the basis of experimental data. Performance parameters such as brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), indicated power (IP), indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), exhaust gas temperature (EGT) are determined for each fuel operation at various loads. It was found that KSOME and its diesel blends show slightly higher BSFC, lower BTE, and higher EGT. IP was more for the blends up to B30 compared to diesel fuel operation, but it significantly reduced in case of the blend B40 indicating more energy losses with this fuel blend. ITE was also lower and ISFC was more for B40 at all loads. The energy analysis indicates higher unaccounted heat losses for the blend B40 which mainly accounts for the losses resulting from incomplete fuel combustion.

Influence of Fuel Supply Timing and Mixture Preparation on the Characteristics of Stratified Charge Compression Ignition Combustion with N-Heptane Fuel

Stratified charge compression ignition (SCCI) combustion was investigated on a single-cylinder, four-stroke diesel engine with n-heptane. A premixed atmosphere was realized by the early injection at the intake port, while the rest of fuel was directly injected into the cylinder. Premixed ratio (defined as the ratio of fuel amount in port injection divided by the total fuel amount in the charge) and fuel supply timing of direct injection were altered to explore their influences on SCCI combustion, emission, and engine performance characteristics. The results show that increased premixed ratio and earlier fuel supply timing can remarkably enhance the peak cylinder temperature and pressure while shortening the main combustion duration. NOx is strongly dependent on fuel supply timing, whereas premixed ratio and equivalence ratio play a secondary role. CO can be effectively reduced by increasing premixed ratio and advancing fuel supply timing. HC rises with increasing premixed ratio but is insensitive to the change of fuel supply timing. Finally, indicated thermal efficiency (ITE) drops with retarded fuel supply timing, and the maximum indicated mean effective pressure (IMEP) can be achieved by optimizing the premixed ratio and fuel supply timing.

Experimental and Numerical Study of Methanol/Dimethyl Ether Dual-Fuel Compound Combustion

This paper experimentally and numerically investigates the effects of injection timing on combustion of a methanol/dimethyl ether (DME) dual-fuel compound at various methanol concentrations. In this dual-fuel compound combustion approach, methanol is directly injected into the cylinder, and DME is injected at the intake port. The experimental results indicate that methanol injection timing has an obvious effect on the heat release process of the dual-fuel compound combustion, and the effect of methanol concentration (i.e., the engine load) on injection timing is also evident. Late injection should be adopted to achieve smooth combustion and low NOx emissions at high methanol concentrations. Moderate injection timing should be adopted to achieve higher indicated thermal efficiency (ITE) at low methanol concentrations. The simulation results, using computational fluid dynamics (CFD) combined with reduced chemical kinetics, show that methanol injected at −26 °CA after top dead center (ATDC) has a remarkable effect on the high-temperature reaction of DME. In the case of injection timing at −26 °CA ATDC, the high-temperature combustion region is concentrated within the combustion chamber, which results in a higher NO concentration. With injection timing at −6 °CA ATDC, by contrast, the high-temperature combustion region is dispersed in the compression clearance and near the chamber wall, which leads to a relatively low NO concentration. Increasing injection pressure is an effective way to shorten the duration of the methanol/DME dual-fuel compound combustion achieved by later injection.

Simultaneous reduction of NO x emission and smoke opacity of biodiesel-fueled engines by port injection of ethanol

In the present study, the detailed combustion characteristics and emissions of biodiesel-fueled engines with premixed ethanol by port injection were investigated. The experiments were carried out on a single-cylinder, four-stroke, natural aspirated direct injection engine at a fixed speed. The heat release analysis indicates that, with the introduction of ethanol fuel by port injection, the ignition timing of the overall combustion event delays remarkably, while the maximum heat release rate increases smoothly. At a leaner fuel/air mixture, the peak value of the heat release rate (HRR) increases slightly, the maximum in-cylinder gas pressure and temperature decrease, and the indicated thermal efficiency (ITE) deteriorates with the increase of ethanol proportion. While at a rich fuel/air mixture, with the increase of the ethanol proportion, the maximum HRR increases rapidly, the overall combustion event is completed at an earlier crank angle. Moreover, the maximum values of the HRR reach the peak point in a certain premixed ratio which ranges from 20% to 40%. Also, the ITE reaches the largest value at this operation point. Due to the introduction of the ethanol fuel by port injection, both the NO x emission and smoke opacity decrease to a very low level under overall operation conditions. During the experimental points of this test, NO x and smoke opacity simultaneously decrease about 35–85% compared to those of the neat biodiesel-fueled engines.