To Top Dead Center Research Articles

Experimental assessment on the performance, emission and combustion characteristics of a safflower oil fueled CI engine with hydrogen gas enrichment

Inducting hydrogen with biodiesel in a compression ignition (CI) engine contributes to improvising the performance characteristics of the engine and minimize long-term issues. Combustion of hydrogen along with intake air impacts positively in air quality by preventing the formation of toxic emissions like hydrocarbons (HC) and carbon monoxide (CO). The benefits of hydrogen such as good diffusion rate, lesser ignition energy and fast flame propagation rate promotes a more homogenously mixed air fuel ratio. This experimental work focuses on enhancement of the performance and combustion characteristics of a direct injection compression ignition (DICI) engine by enriching the biodiesel with various levels of hydrogen gas supplement at the intake manifold. The brake thermal efficiency of the engine with safflower oil biodiesel is 31.15 % which is far inferior to that of diesel with 34 %. As an effort to improve the performance characteristics of the CI engine, hydrogen gas is inducted at 4 %, 8 % and 12 % energy share. HC, CO and smoke emission decreases by 15.09 %, 34.6 % and 18 % respectively compared to neat biodiesel at full load of 5.2 kW. An opposite trend is observed in NOx emissions which are raised from 1650 ppm to 1852 ppm. A 12.2 % increase in NOx emissions are realized due to homogenous flammable mixture that combusts closer to Top dead center (TDC). The hydrogen enrichment with safflower oil biodiesel influences the combustion characteristics in a positive vein except for the NOx emissions, which could be minimized through the use of retrofit devices like selective catalytic reducer, diesel oxidation catalyst etc.

Emissions and Performance of a Hybrid Hydrogen-gasohol E20 Fueled Si Engine

T his paper has investigated the effects of an alternative hybrid hydrogen-gasohol E20 fueled spark ignition engine on engine performance and exhaust pollutants. A hydrogen mixture with gasohol E20 was performed in an external mixture formation by installing a hydrogen fuel injection kit into the intake manifold area which is responsible for injecting hydrogen fuel into the inside of the engine’s cylinder. The hydrogen energy fraction in the intake was gradually increased from 3% to 9% ignition degree in the range of 20°, 25°, 30° and 35° before top dead center were controlled by using the electronic control unit to study the optimal condition for a four-stroke single-cylinder engine. In the steady-state test condition with half-open throttle under the variable load engine at 28%, 42%, 56%, and 70% of maximum engine torque, the engine can be available satisfactorily for an average relative air-fuel ratio (λ) value of 1.2 for hybrid hydrogen-gasohol E20 fuel. The results indicated that when the increase of hydrogen volume fraction. Postponing the spark timing was closer to top dead center (TDC) at 25° BTDC, the brake power and thermal engine efficiency increases. It is also noted that postponing the spark timing also caused NOx, HC and CO emissions to decrease. NOx emissions increased as the hydrogen volume fraction increased, whereas HC and CO emissions decreased.

High-pressure direct injection of methanol and pilot diesel: A non-premixed dual-fuel engine concept

In order to reduce the climate impacts, methanol produced from carbon-neutral methods plays an important role. Due to its oxygen content and high latent heat, methanol combustion can achieve low soot and NOx emissions. In the present study, direct injection (DI) of methanol is investigated in a non-premixed dual-fuel (DF) setup with diesel pilot. The present DF engine study is carried out via a specially-designed new cylinder head operating with a centrally located methanol injector and with an off-centered diesel pilot injector. The target is to inject methanol close to top dead center (TDC) in a similar fashion as in standard diesel combustion enabling robust operation with high efficiency. The ignition of the DI methanol is achieved with an almost simultaneously injected diesel pilot. The experiments were conducted in a single-cylinder heavy-duty research engine at a constant engine speed of 1500 rpm with a compression ratio of 16.5. The indicated mean effective pressure (IMEP) varied between 4.2 and 13.8 bar while the methanol substitution ratio was swept between 45 and 95%. In addition, the diesel pilot and methanol injection timings were varied for optimum efficiency and emissions. The introduced non-premixed DF concept using methanol as the main fuel showed robust ignition characteristics, stable combustion, and low CO and HC emissions. The results indicate that increasing both the load and the methanol substitution ratio can increase the thermal efficiency and the stability of combustion (lower COV) together with decreased CO and HC emissions.

Effects of H2/CO addition on knock tendency and lean limit in a natural gas SI engine

Dedicated exhaust gas recirculation is an attractive way to improve the performances of internal combustion engines. Hydrogen (H2) and carbon monoxide (CO) are primary combustible components in the reforming cylinder. Detailed knowledge of the effects of H2/CO on knock tendency and intensity and even lean limit is essential for the better utilization of this sort of technologies. In this paper, the influences of H2/CO on knock characteristics and lean limit are experimentally investigated. The experimental results indicate that the lean limit could be extended by 5–10% with 1% and 2% H2/CO addition, respectively and meanwhile their addition significantly decreases THC and CO emissions despite of the slight increase in NOx emission. The knock-limited spark advance angles are determined using a pressure-based method. H2/CO addition significantly increases knock tendency and intensity due to the increased energy density and faster flame propagation speed. Knock intensity increases linearly as knock onset angle is advanced towards to top dead center (TDC) due to higher end-gas temperature. However, the increase in knock intensity caused by H2/CO addition is closely related to faster flame propagation speed. The sensitivity analysis reveals the crucial reaction in promoting flame propagation with H2/CO addition is the branching reaction H + O2 = O + OH. And their addition also increases the reaction rates of another two dominating reactions CH3 + HO2 = CH3O + OH and CO + OH = CO2 + H. 1% and 2% H2/CO addition extend lower equivalence ratio limits by 14% and 26% which is beneficial for further efficiency improvement and emission reduction.

Spark timing effect on performance of gasoline engine fueled with mixture of hydrogen–gasoline

Ignition timing is heavily related to flame speed, which has great effect on SI engines performance. Due to that the flame speed for the fuel mixture that was formed by adding hydrogen to the traditional fuel was greatly changed, the ignition timing should be changed to attain suitable performance of the engine when used this mixture of fuels. The following experiments were performed to investigate the effect of ignition timing for different hydrogen percentages which mixed with gasoline fuel on a single-cylinder engine, four strokes. The tested hydrogen percentages by volume were 24%, 28%, 29%, 31%, and 49%. The analysis for engine performance was carried out at ignition timing positions (30°, 35°, 40° BTDC). The results indicated that when the ignition timing was closer to top dead center (TDC) i.e at 30° BTDC, the fuel consumption decreases and thermal engine efficiency increases. It is also noted that HC% increases and CO% were increased when spark time was more advanced for the same hydrogen concentration i.e at 40° BTDC.

Effects of combustion duration characteristic on the brake thermal efficiency and NOx emission of a turbocharged diesel engine fueled with diesel-LNG dual-fuel

The diesel-LNG (liquefied natural gas) dual-fuel combustion mode was conducted on a high-pressure common-rail six-cylinder diesel engine to find an assistant parameter to assess the brake thermal efficiency (ηe) and nitrogen oxides (NOx) emission of the diesel-LNG dual-fuel engine. The results show that the diesel injection timing has a prominent impact on the centroid angle of combustion duration (α) which is closely related to ηe and NOx emission. At low and medium loads, when α is near to top dead center (TDC) and is after TDC, the ηe and NOx emission are higher. Nevertheless, when α is before TDC, the result of NOx emission is opposite. Therefore, for optimal ηe and NOx emission at low and medium loads, it would be the best way altering diesel injection timing to retard α to ATDC and ensuring α in 1–2°CA ATDC.

Experimental investigation on the influence of engine operating conditions on combustion and nanoparticle emission characteristics of a small DI diesel engine

The influence of variations in engine speed, injection pressure, injection timing, and multiple injection strategies on the combustion and nanoparticle characteristics of a small Direct injection (DI) diesel engine was experimentally investigated. To measure the size distribution and number concentration of particle emissions, a rotating disk thermo-diluter (dilution system), a Condensation particle counter (CPC), and a Scanning mobility particle sizer (SMPS) were used. The injection pressure was changed from 60 MPa to 120 MPa, at an engine speed of 1200 rpm. Injection timing was varied from Before top dead center (BTDC) 40˚ to Top dead center (TDC). To investigate the effect of multiple-injection strategies, the injection strategies consisted of two pulse signals with different dwell time. The experimental results show that the peak combustion pressure and Rate of heat release (ROHR) profile are increased and ignition delay is shortened with the increase of injection pressure from 60 MPa to 120 MPa. The concentration of soot emission for 120 MPa is lower than that of 60 MPa at advanced injection timing from TDC up to BTDC 25°. As the injection timing advances to over BTDC 30°, soot emissions rapidly increase and the high injection pressure case (120 MPa) creates more emissions than the 60 MPa case. The overall trends of total particle number are relatively increased with high injection pressure for single injection conditions. In the advanced injection timings of over BTDC 30°, the trend of total particle number is high for all injection pressures. For multiple injections, the peak combustion pressures and ROHR of multiple-injection strategies are slightly lower compared with those of single-combustion results. Comparing the multiple injection strategies, soot emission is reduced with the retard of second injection timing (-30°+5°). The overall trends of particle size and total number for the 7 mg+3 mg case revealed the lowest level compared with other cases, which is 50% lower than that for the 5 mg+5 mg case. When compared with single injection results, the total particle number and Dp of multiple injection cases were eventually lower.

Numerical study of effects of reformed exhaust gas recirculation (REGR) on dimethyl ether HCCI combustion

The effects of reformed exhaust gas recirculation (REGR) on combustion and emissions of dimethyl ether (DME) homogeneous charge compression ignition (HCCI) engines are studied by multi-dimensional CFD coupled with chemical kinetic model. The results show that REGR combing EGR and DME reformed gases (DRG) improves combustion and emissions. REGR can delay ignition time by both EGR and DRG, and makes main combustion closer to top dead center (TDC), which is beneficial to reducing compression negative work and broadening load range of HCCI engines. The interaction of DRG and EGR helps avoid too high pressure rise rate or low power performance when being applied independent of each other. HC, CO and NOx emissions can be controlled simultaneously by REGR. Both advantages of DRG and EGR are used to decrease the emissions of HCCI engines by REGR, while the disadvantages of high emissions are alleviated when one of them is applied.

Effects of High EGR Rate on Dimethyl Ether (DME) Combustion and Pollutant Emission Characteristics in a Direct Injection Diesel Engine

This study investigated the effects of high exhaust gas recirculation (EGR) rates on dimethyl ether (DME) fuel combustion performance, exhaust emissions and particle emission characteristics in a small direct injection diesel engine under various injection timings. To examine the effect of EGR and injection timings, the experiment was performed under high EGR rates (0%, 30%, 50%) and injection timings were varied from 40° before top dead center (BTDC) to top dead center (TDC) of the crank angle to examine the effects of early injection of DME fuel. The combustion pressures and heat release rates for different EGR rates followed similar trends. As the injection timing was advanced, the indicated mean effective pressure (IMEP) differed little in response to EGR rate in the range from TDC to 25° BTDC, and more for crank angles beyond 25° BTDC. DME combustion exhibited very little soot emission, but soot emission increased slightly with EGR rate. The use of high EGR during combustion produced very low NOx concentrations but increased HC and CO emissions for advanced injection timings from 25° BTDC to 40° BTDC. The use of EGR increased both the emissions of total particle number and particle volume over the whole range of the injection timings; for all cases, total particle volume decreased as injection timing was advanced.

Influence of Emulsified Palm Biodiesel as Pilot Fuel in a Biogas Run Dual Fuel Diesel Engine

This study attempts to explore the influence of emulsified palm biodiesel as a pilot fuel in a biogas run dual fuel engine. The intention is to achieve diesel-equivalent performance from a diesel engine, together with a reduction in engine emissions, with complete replacement of fossil diesel with renewable fuels. The results of this study are compared to those for a neat biodiesel (Jatropha)-biogas dual fuel engine run at identical engine settings. For baseline comparison, the results are also compared with a standard diesel run. The results show that with the presence of biogas, emulsified biodiesel as a pilot fuel can present a better dual fuel efficiency (41%) and a lower energy consumption (38%) than neat biodiesel in a piloted study. Also, the presence of a microexplosion of emulsified biodiesel was found to reduce the pilot fuel consumption with the presence of biogas, especially at lower loads, where the burning rate of biogas usually slows down due to the lean gas-air mixture and cooler charge temperature. In addition, emulsified palm biodiesel successfully brings the peak cylinder pressure (PCP) closer (8°ATDC) to top dead center (TDC). This elevates the magnitude of the PCP, which increases the expansion ratio and hence improves engine efficiency. With the presence of emulsified biodiesel, the supply of biogas is found to get reduced, especially at higher loads, which in turn reduces the hydrocarbon emission. However, other emission characteristics are not as exciting, and hence emulsified biodiesel in biogas dual fuel mode needs to be further explored at various engine-operating characteristics in order to obtain a superior emission performance.

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.

Effect of Fuel Injection Timing and Injection Pressure on Combustion and Odorous Emissions in DI Diesel Engines

This study investigated the effect of fuel injection timing and injection pressure on combustion and odorous emissions in a direct injection diesel engine. Injection timings from 15 deg before top dead center (BTDC) to top dead center (TDC) and injection pressures from 20 MPa to 120 MPa were tested. In emissions, exhaust odor, irritation, aldehydes, total hydrocarbon, and hydrocarbon components are compared in different injection timings and injection pressures condition. Injection timings where main combustion takes place very close to TDC are found to show minimum odorous emissions. Moderate injection pressures (60–80 MPa) showed lower emissions including odor and irritation due to proper mixture formation. Below the injection pressure of 40 MPa, and over 80 MPa, emissions become worse. Combustion analysis is performed by taking cylinder pressures after engine warm-up for different injection timings and injection pressures and analyzing cylinder temperatures and heat release rates. Cylinder pressures and temperatures are gradually decreased when injection timings are retarded. Ignition delay becomes shortest at 5–10 deg BTDC injection timings. The peak cylinder pressure and temperature are increased with higher injection pressures. The shortest ignition delay and minimum emissions is found at around 60 MPa of injection pressure.

Experimental Investigation of Combustion Characteristics and Emissions of an Indirect Injection Diesel Engine under Different Operating Conditions

In this study, the effects of engine-operating conditions on the combustion characteristics and emissions of an indirect injection (IDI) diesel engine have been experimentally investigated. The engine tests were conducted on 20, 30, and 40 N m constant loads and at full load condition. The experimental results show that the maximum cylinder gas pressures (Pmax) increased with an increasing engine speed and load. The location of the maximum cylinder gas pressure closed to top dead center (TDC) at high engine load. The starts of combustion (SOC) points closed to TDC at high engine speeds. The ignition delay (ID) slightly decreased with the increase of the engine loads, and it increased with an increasing engine speed. However, as the total combustion duration (TC) increased with an increasing engine load, it decreased with high engine speeds. The exhaust emissions, such as nitrogen oxides (NOx), smoke opacity, unburned hydrocarbon (HC), and carbon monoxide (CO), were also discussed for different operating c...