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Abstract : Vol.37No.3(2002.9)
Special Issure : Challenges in Realizing Clean High-Performance
Diesel Engines
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Review
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| P.1 |
Research
and Development Trends in Combustion and Aftertreatment
Systems for Next-Generation HSDI Diesel Engines |
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Kiyomi Nakakita
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Recently, the performance and exhaust emissions of
high-speed direct injection (HSDI) diesel engines for
passenger cars have been rapidly improved. In these
engines, the power and torque densities have reached
50-60 kW/l and 160-170 Nm/l, respectively. In addition,
the noise, vibration and harshness (NVH) and exhaust
emissions have been decreasing toward a level that is
comparable to that of gasoline engines. Furthermore,
the maximum brake thermal efficiency has reached 42-43%
and both city and highway fuel economy is excellent.
Therefore, the percentage of diesel passenger cars in
Europe has been increasing remarkably and is forecasted
to reach 48% in 2007.
The developments of common-rail (CR) injection systems,
high-efficiency aftertreatment devices such as the diesel
particulate filter (DPF) and catalysts, and advanced
electronic control systems are listed as major technical
backgrounds of the progress in HSDI diesel engines.
In the present review, recent trends in research and
development of the above-listed component technologies,
primarily regarding combustion and aftertreatment systems,
are outlined. Finally, critical technical areas that
must be addressed in order to realize an ultra-clean
and high-performance diesel engine are presented.
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Research Report
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| P.9 |
Achieving
Lower Exhaust Emissions and Better Performance in an HSDI
Diesel Engine with Multiple Injection |
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Yoshihiro Hotta, Minaji Inayoshi,
Kiyomi Nakakita
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The effects of multiple injection on exhaust emissions
and performance in a small HSDI (High Speed Direct Injection)
Diesel engine are investigated. It is possible to increase
the maximum torque, which is limited by the exhaust
smoke number, while decreasing the combustion noise
under low speed, full load conditions by advancing the
timing of the pilot injection. Dividing this early-timed
pilot injection into a series of smaller injections
serves to further decrease the noise while suppressing
the increase of HC emission and fuel consumption. These
effects result from the enhanced heat release rate of
the pilot injection fuel, which is due to the reduced
amount of adhered fuel on the cylinder wall. At light
loads, the amount of pilot injection fuel must be reduced,
and the injection must be timed just prior to the main
injection in order to suppress a possible increase in
smoke and HC. After-injection, a small amount of fuel
injected immediately after the end of the main injection,
reduces smoke, HC and fuel consumption.
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| P.17 |
Smoke
Reduction Methods Using Shallow-Dish Combustion Chamber
in an HSDI Common-Rail Diesel Engine |
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Yoshihiro Hotta, Kiyomi Nakakita,
Takayuki Fuyuto, Minaji Inayoshi
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The cause of exhaust smoke from a small DI Diesel engine
having small-orifice-diameter nozzles and a common-rail
F.I.E. under the high-speed and high-load condition
was investigated. In addition, methods by which to reduce
this exhaust smoke were explored. Exhaust emission tests,
in-cylinder observations and three-dimensional numerical
analyses were performed. The following points were clarified
during this study.
Under the abovementioned conditions, fuel sprays are
easily conveyed to the squish area by a strong reverse
squish. Therefore, the air in the piston cavity is not
used effectively. Suppressing the airflow in the piston
cavity by using a shallow-dish type combustion chamber
decreases the excessive outflow of the fuel-air mixture
into the squish area and allows full use of the air
in the piston cavity. Hence, the exhaust smoke is reduced.
This results in increased specific power, which is limited
by the amount of exhaust smoke.
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| P.25 |
NOx
Selective Catalytic Reduction over Pt SupportedCatalyst
Promoted by Zeolite and CeO2-ZrO2 |
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Toshitaka Tanabe, Miho Hatanaka,
Ryusuke Tsuji, Hirofumi Shinjoh
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The emission control of NOx in exhaust
gases is one of the greatest engineering challenges
to extend the practical and commercial application of
diesel and lean burn engines. One solution is selective
NOx reduction using hydrocarbons in an oxidizing atmosphere.
We mainly focused on catalytic reactions under temperature
excursion because of the resemblance to conditions prevailing
in real automotive exhaust. Adsorbed hydrocarbon on
zeolite was found to be highly effective in reducing
NOx at elevating temperature. Thus, we proposed a novel
catalyst formulation involving zeolite and CeO2-ZrO2.
Our catalyst concept consists of supported Pt on thermally
stable oxides (such as SiO2), zeolite and
CeO2-ZrO2. Hydrocarbons adsorb
on zeolite at low temperatures and migrate to the Pt
surface at elevating temperature to reduce NOx. The
active oxygen generated from CeO2-ZrO2
suppresses the poisoning effect of hydrocarbons at low
temperature, promoting NOx reduction.
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| P.32 |
Numerical
Optimization of HC Supply for HC-DeNOx System (1) Numerical
Modeling of HC-DeNOx Catalyst |
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Yoshihide Watanabe
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A one-dimensional model was used to
describe the transient heat and mass transfer as well
as the hydrocarbon (HC) adsorption-desorption and the
heterogeneous reactions of NOx and HC in diesel engine
exhaust. The behavior of HC and NOx reactions and the
HC adsorption-desorption in diesel exhaust have been
simulated successfully under 10-15 driving cycles. A
model for DeNOx catalytic reaction which takes into
consideration HC adsorption and desorption and is capable
of predicting the performance of DeNOx catalyst using
diesel fuel as a supplemental reductant has been successfully
developed.
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| P.40 |
Numerical
Optimization of HC Supply for HC-DeNOx System (2) Optimization
of HC Supply Control |
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Matsuei Ueda
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A new method that optimizes the control
map of hydrocarbon addition to the diesel exhaust gas
for hydrocarbon selective catalyst reduction has been
developed. This method is comprised of a numerical HC-DeNOx
catalyst model and a new optimization technique using
Evolutionary Programming based on the evolution of living
organisms. The numerical HC-DeNOx catalyst model was
also used to describe HC adsorption-desorption.1)
As a result of this evaluation, the number of calculations
to obtain the optimal control map with this method was
less by one third than that of all maps surveys. By
using the obtained optimal control map, the NOx conversion
under the Japanese 10-15 mode of the inlet-side heavily
Platinum-loaded catalyst was higher by 13% than that
of the uniformly Platinum-loaded catalyst in spite of
the same amount of the loaded platinum. This was because
the heavily platinum-loaded catalyst could start the
NOx reduction at a lower temperature, enabling the optimal
control map to keep the catalyst temperature within
the temperature window of the catalyst for a longer
time.
1) Watanabe, Y., et al. : "Development
of a Model for the Lean NOx Catalytic Reaction with
Hydrocarbon Adsorption and Desorption", Appl. Catal.
B, Environm., 31-3(2001) 221-228
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| P.46 |
Effect
of Hydrocarbon Molecular Structure on Diesel Exhaust Emissions |
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Kazuhiro Akihama, Yoshiki Takatori,
Kiyomi Nakakita
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In order to determine diesel fuel characteristics
that might influence particulate matter (PM) emission,
we have conducted a detailed investigation that combines
combustion/exhaust emission measurements, in-cylinder
observations, fuel analyses and chemical reactor experiments.
A comparison between three representative diesel fuels,
viz., "Base" (Japanese market fuel), ﾒImprovedﾓ(lighter
fuel with lower aromatics) and Swedish ﾒClass-1ﾓ yielded
the following results: (1) The amount of PM emission
decreases in the order of "Base" > "Class-1"
> "Improved". Unexpectedly enough, "Class-1"
produces more PM than "Improved" despite its
significantly lower distillation temperature, and lower
aromatics and sulfur content. (2) There is little difference
in the combustion characteristics of the three fuels.
(3) Only "Class-1" contains significant quantities
of iso and naphthenic structures. (4) Flow reactor pyrolysis
shows that "Class-1" produces the largest
amount of PM precursors, such as benzene and toluene.
These results suggest that the presence of branched
and ring structures can increase exhaust PM emissions.
This finding was confirmed by flow-reactor and shock
tube experiments using hexanes, which revealed that
iso- and cyclo-paraffins produce more benzene and soot
than n-paraffins do. The results obtained in this study
indicate that the specific molecular structure of the
paraffinic components needs to be considered as one
of the diesel fuel properties closely related to PM
formation.
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