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Technical Paper

An Investigation of the Transient DPF Pressure Drop under Cold Start Conditions in Diesel Engines

2017-10-08
2017-01-2372
To monitor emission-related components/systems and to evaluate the presence of malfunctioning or failures that can affect emissions, current diesel engine regulations require the use of on-board diagnostics (OBD). For diesel particulate filters (DPF), the pressure drop across the DPF is monitored by the OBD as the pressure drop is approximately linear related to the soot mass deposited in a filter. However, sudden acceleration may cause a sudden decrease in DPF pressure drop under cold start conditions. This appears to be caused by water that has condensed in the exhaust pipe, but no detailed mechanism for this decrease has been established. The present study developed an experimental apparatus that reproduces rapid increases of the exhaust gas flow under cold start conditions and enables independent control of the amount of water as well as the gas flow rate supplied to the DPF.
Technical Paper

Semi-Premixed Diesel Combustion with Twin Peak Shaped Heat Release Using Two-Stage Fuel Injection

2016-04-05
2016-01-0741
Characteristics of semi-premixed diesel combustion with a twin peak shaped heat release (twin combustion) were investigated under several in-cylinder gas conditions in a 0.55 L single cylinder diesel engine with common-rail fuel injection, super-charged, and with low pressure loop cooled EGR. The first-stage combustion fraction, the second injection timing, the intake oxygen concentration, and the intake gas pressure influence on thermal efficiency related parameters, the engine noise, and the exhaust gas emissions was systematically examined at a middle engine speed and load condition (2000 rpm, 0.7 MPa IMEP). The twin peak shaped heat release was realized with the first-stage premixed combustion with a sufficient premixing duration from the first fuel injection and with the second fuel injection taking place just after the end of the first-stage combustion.
Journal Article

Diesel Engine Combustion Noise Reduction by the Control of Timings and Heating Values in Two Stage High Temperature Heat Releases

2016-04-05
2016-01-0731
Reductions in combustion noise are necessary in high load diesel engine operation and multiple fuel injections can achieve this with the resulting reductions in the maximum rate of pressure rise. In 2014, Dr. Fuyuto reported the phenomenon that the combustion noise produced in the first combustion can be reduced by the combustion noise of the second fuel injection, and this has been named “Noise Cancelling Spike Combustion (NCS combustion)”. To investigate more details of NCS combustion, the effects of timings and heating values of the first and second heat releases on the reduction of overall combustion noise are investigated in this paper. The engine employed in the research here is a supercharged, single cylinder DI diesel engine with a high pressure common rail fuel injection system.
Journal Article

Low Temperature Premixed Diesel Combustion with Blends of Ordinary Diesel Fuel and Normal Heptane

2015-11-17
2015-32-0754
Premixed diesel combustion blending high volatility fuels into diesel fuel were investigated in a modern diesel engine. First, various fractions of normal heptane and diesel fuel were examined to determine the influence of the blending of a highly ignitable and volatile fuel into diesel fuel. The indicated thermal efficiency improves almost linearly with increasing normal heptane fraction, particularly at advanced injection timings when the fuel is not injected directly into the piston cavity. This improvement is mainly due to decreases in the other losses, ϕother which are calculated with the following equation based on the energy balance. ηu: The combustion efficiency calculated from the exhaust gas compositions ηi: The indicated thermal efficiency ϕex: The exhaust loss calculated from the enthalpy difference between intake and exhaust gas The decreases in the other losses with normal heptane blends are due to a reduction in the unburned fuel which does not reach the gas analyzer.
Technical Paper

Improvement of Combustion and Emissions in a Dual Fuel Compression Ignition Engine with Natural Gas as the Main Fuel

2015-04-14
2015-01-0863
Dual fuel combustion with premixed natural gas as the main fuel and diesel fuel as the ignition source was investigated in a 0.83 L, single cylinder, DI diesel engine. At low loads, increasing the equivalence ratio of natural gas to around 0.5 with intake throttling makes it possible to reduce the THC and CO emissions as well as to improve the thermal efficiency. At high loads, increasing the boost pressure moderates the combustion, but increases the THC and CO emissions, resulting in deterioration of the thermal efficiency. The EGR is essential to suppress the rapid combustion. As misfiring occurs with a compression ratio of 14.5 and there is excessively rapid combustion with 18.5 compression ratio, 16.5 is a suitable compression ratio.
Technical Paper

Optimization of Heat Release Shape and the Connecting Rod Crank Radius Ratio for Low Engine Noise and High Thermal Efficiency of Premixed Diesel Engine Combustion

2015-04-14
2015-01-0825
Premixed diesel combustion offers the potential of high thermal efficiency and low emissions, however, because the rapid rate of pressure rise and short combustion durations are often associated with low temperature combustion processes, noise is also an issue. The reduction of combustion noise is a technical matter that needs separate attention. Engine noise research has been conducted experimentally with a premixed diesel engine and techniques for engine noise simulation have been developed. The engine employed in the research here is a supercharged, single cylinder DI diesel research engine with a high pressure common rail fuel injection system. In the experiments, the engine was operated at 1600 rpm and 2000 rpm, the engine noise was sampled by two microphones, and the sampled engine noise was averaged and analyzed by an FFT sound analyzer.
Technical Paper

Dual Fuel Diesel Combustion with Premixed Ethanol as the Main Fuel

2014-10-13
2014-01-2687
Dual fuel combustion with premixed ethanol as the main fuel and direct injection of diesel fuel as an ignition source poses problems including large unburned emissions and excessively rapid combustion. In this report the influence of compression ratios, injection timings of diesel fuel, and intake oxygen concentrations was systematically investigated in a modern diesel engine. The combustion process was classified into three stages: the first rapid combustion of diesel fuel and the ethanol mixture entrained into the diesel fuel spray; the second mild combustion with flame propagation of the ethanol mixture; and the third rapid combustion with auto-ignition of the unburned ethanol mixture without knocking. The third stage combustion occurs occasionally at several operating conditions and has been termed as PREMIER (premixed mixture ignition in the end-gas region) combustion.
Technical Paper

Combustion Noise Analysis of Premixed Diesel Engine by Engine Tests and Simulations

2014-04-01
2014-01-1293
When fuel is vaporized and mixed well with air in the cylinder of premixed diesel engines, the mixture auto-ignites in one burst resulting in strong combustion noise, and combustion noise reduction is necessary to achieve high load premixed diesel engine operation. In this paper, an engine noise analysis was conducted by engine tests and simulations. The engine employed in the experiments was a supercharged single cylinder DI diesel engine with a high pressure common rail fuel injection system. The engine noise was sampled by two microphones and the sampled engine noise was averaged and analyzed by an FFT sound analyzer. The engine was equipped with a pressure transducer and the combustion noise was calculated from the power spectrum of the FFT analysis of the in-cylinder pressure wave data from the cross power spectrum of the sound pressure of the engine noise.
Journal Article

Combustion Characteristics of Emulsified Blends of Water and Diesel Fuel in a Diesel Engine with Cooled EGR and Pilot Injection

2013-10-15
2013-32-9022
Water and diesel fuel emulsions containing 13% and 26% water by volume were investigated in a modern diesel engine with relatively early pilot injection, supercharging, and cooled EGR. The heat release from the pilot injection with water emulsions is retarded toward the top dead center due to the poor ignitability, which enables larger pilot and smaller main injection quantities. This characteristic results in improvements in the thermal efficiency due to the larger heat release near the top dead center and the smaller afterburning. With the 26% water emulsion, mild, smokeless, and very low NOx operation is possible at an optimum pilot injection quantity and 15% intake oxygen with EGR at or below 0.9 MPa IMEP, a condition where large smoke emissions are unavoidable with regular unblended diesel fuel. Heat transfer analysis with Woschni's equation did not show the decrease in cooling loss with the water emulsion fuels.
Journal Article

Influence of Fuel Properties on Operational Range and Thermal Efficiency of Premixed Diesel Combustion

2013-10-15
2013-32-9054
The influence of fuel properties on the operational range and the thermal efficiency of premixed diesel combustion was evaluated with an ordinary diesel fuel, a primary reference fuel for cetane numbers, three primary reference fuels for octane numbers, and two normal heptane-toluene blend fuels in a single-cylinder DI diesel engine. The fuel injection timing was set at 25°CA BTDC and the maximum rate of pressure rise was maintained below 1.0 MPa/°CA when lowering the intake oxygen concentration by cooled EGR. With increasing octane numbers, the higher intake oxygen concentration can be used, resulting in higher indicated thermal efficiency due to a higher combustion efficiency. The best thermal efficiency at the optimum intake oxygen concentration with the ordinary diesel fuel is lower than with the primary reference fuels with the similar ignitability but higher volatility.
Technical Paper

Visualization and Heat Release Analysis of Premixed Diesel Combustion with Various Fuel Ignitabilities and Oxygen Concentrations in a Constant Volume Combustion Vessel

2013-04-08
2013-01-0899
Low NOx and soot free premixed diesel combustion can be realized by increasing ignition delays in low oxygen atmospheres, as well as the combustion here also depends on fuel ignitability. In this report single intermittent spray combustion with primary reference fuels and a normal heptane-toluene blend fuel under several oxygen concentrations in a constant volume combustion vessel was analyzed with high-speed color video and pressure data. Temperature and KL factor distributions are displayed with a 2-D two-color method. The results show that premixing is promoted with a decrease in oxygen concentration, and the local high temperature regions, above 2200 K, as well as the duration of their appearance decreases with the oxygen concentration. With normal heptane, mild premixed diesel combustion can be realized at 15 vol% oxygen and there is little luminous flame.
Journal Article

Combustion and Emissions with Bio-alcohol and Nonesterified Vegetable Oil Blend Fuels in a Small Diesel Engine

2012-10-23
2012-32-0017
Combustion and exhaust gas emissions of alcohol and vegetable oil blends including a 20% ethanol + 40% 1-butanol + 40% vegetable oil blend and a 50% 1-butanol + 50% vegetable oil blend were examined in a single cylinder, four-stroke cycle, 0.83L direct injection diesel engine, with a supercharger and a common rail fuel injection system. A 50% diesel oil + 50% vegetable oil blend and regular unblended diesel fuel were used as reference fuels. The boost pressure was kept constant at 160 kPa (absolute pressure), and the cooled low pressure loop EGR was realized by mixing with a part of the exhaust gas. Pilot injection is effective to suppress rapid combustion due to the lower ignitability of the alcohol and vegetable oil blends. The effects of reductions in the intake oxygen concentration with cooled EGR and changes in the fuel injection pressure were investigated for the blended fuels.
Technical Paper

HCCI Combustion Control by DME-Ethanol Binary Fuel and EGR

2012-09-10
2012-01-1577
The HCCI engine offers the potential of low NOx emissions combined with diesel engine like high efficiency, however HCCI operation is restricted to low engine speeds and torques constrained by narrow noise (HCCI knocking) and misfiring limits. Gasoline like fuel vaporizes and mixes with air, but the mixture may auto-ignite at the same time, leading to heavy HCCI knocking. Retarding the CA50 (the crank angle of the 50% burn) is well known as a method to slow the maximum pressure rise rate and reduce HCCI knocking. The CA50 can be controlled by the fuel composition, for example, di-methyl ether (DME), which is easily synthesized from natural gas, has strong low temperature heat release (LTHR) characteristics and ethanol generates strong LTHR inhibitor effects. The utilization of DME-ethanol binary blended fuels has the potential to broaden the HCCI engine load-speed range.
Technical Paper

Combustion Characteristics of Emulsified Blends of Aqueous Ethanol and Diesel Fuel in a Diesel Engine with High Rates of EGR and Split Fuel Injections

2011-08-30
2011-01-1820
Silent, clean, and efficient combustion was realized with emulsified blends of aqueous ethanol and diesel fuel in a DI diesel with pilot injection and cooled EGR. The pilot injection sufficiently suppressed the rapid combustion to acceptable levels. The thermal efficiency with the emulsified fuel improved as the heat release with the pilot injection was retarded to near top dead center, due to poor ignitability and also due to a reduction in afterburning. With the emulsified fuel containing 40 vol% ethanol and 10 vol% water (E40W10), the smokeless operation range can be considerably extended even under low fuel injection pressure or low intake oxygen content conditions.
Technical Paper

Study on Simple and High-Speed Diesel Combustion Model with Wall Impingement

2011-08-30
2011-01-1846
To design diesel engines adapted to future exhaust gas regulation, it would be advantageous to have a driving mode simulation for vehicle performance and exhaust emissions, including after-treatment systems. The combustion model for this objective must be able to simulate the engine performance in very short time. We have tried to develop such diesel engine combustion model by adding the improvements to the Hiroyasu model. In this paper, we detail the improvements that were added to this model and comparisons the calculated results by the improved model with experimental result.
Journal Article

Analysis of the Trade-off between Soot and Nitrogen Oxides in Diesel-Like Combustion by Chemical Kinetic Calculation

2011-08-30
2011-01-1847
This study makes use of the detailed mechanisms of n-heptane combustion, from gas reactions to soot particle formation and oxidation, and a two-stage model based on the CHEMKIN reactor network is developed and used to investigate the trade-off between soot and NOx emissions. The effects of the equivalence ratio, EGR, ambient pressure and temperature, and initial particle diameter are observed for various residence times. The results show that high rates of NOx formation are unavoidable under conditions where high reduction rates of soot particles are obtained. This suggests that suppression of the amount of soot during the formation stage is essential for simultaneous reductions in engine-out soot and NOx emissions.
Journal Article

Improvement in DME-HCCI Combustion with Ethanol as a Low-Temperature Oxidation Inhibitor

2011-08-30
2011-01-1791
Port injection of ethanol addition as an ignition inhibitor was implemented to control ignition timing and expand the operating range in DME fueled HCCI combustion. The ethanol reduced the rate of low-temperature oxidation and consequently delayed the onset of the high-temperature reaction with ultra-low NOx over a wide operating range. Along with the ethanol addition, changes in intake temperature, overall equivalence ratio, and engine speed are investigated and shown to be effective in HCCI combustion control and to enable an extension of operation range. A chemical reaction analysis was performed to elucidate details of the ignition inhibition on low-temperature oxidation of DME-HCCI combustion.
Technical Paper

Improvements to Premixed Diesel Combustion with Ignition Inhibitor Effects of Premixed Ethanol by Intake Port Injection

2010-04-12
2010-01-0866
Premixed diesel combustion modes including low temperature combustion and MK combustion are expected to realize smokeless and low NOx emissions. As ignition must be delayed until after the end of fuel injection to establish these combustion modes, methods for active ignition control are being actively pursued. It is reported that alcohols including methanol and ethanol strongly inhibit low temperature oxidation in HCCI combustion offering the possibility to control ignition with alcohol induction. In this research improvement of diesel combustion and emissions by ethanol intake port injection for the promotion of premixing of the in-cylinder injected diesel fuel, and by increased EGR for the reduction of combustion temperature.
Technical Paper

Expansion of the Operating Range with In-Cylinder Water Injection in a Premixed Charge Compression Ignition Engine

2002-05-06
2002-01-1743
The control of fuel ignition timing and suppression of rapid combustion in a premixed charge compression ignition (PCCI) engine was attempted with direct in-cylinder injection of water as a reaction suppressor. The water injection significantly reduced the heat release at low temperature oxidation, which suppressed the increase in charge temperature after the low temperature oxidation and the rapid combustion caused by the high temperature oxidation. The possible engine operating range with ultra low NOx and smokeless combustion was extended to a higher load range with the water injection. Rapid combustion was suppressed by reductions in the maximum in-cylinder gas temperature due to water injection while the combustion efficiency suffered. Therefore, the maximum charge temperature needs to be controlled within an extremely limited range to maintain a satisfactory compromise between mild combustion and high combustion efficiency.
Technical Paper

Thermal Plastic-elastic Creep Analysis of Engine Cylinder Head

2002-03-04
2002-01-0585
Critical for the use of aluminum alloys for cylinder heads are strength and durability. In our study, the mechanism of the low cycle fatigue and creep was clarified based on the mechanical properties of aluminum alloys, such as tensile, compressive, thermal fatigue and creep characteristics, which were determined by conducting tests on test pieces. The behavior of a cylinder head under cyclic thermal condition was represented by using a high-precision analysis method with cyclic creep taken into consideration. Moreover, the high-precision analysis method turned out to be effective in estimating a low cycle fatigue life under the cyclic thermal condition.
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