Search Results

This paper shows development challenges for 6 liter heavy duty off-road diesel engines to meet the Tier4 final emission regulations with a base diesel engine compliant with Tier4 interim emission regulations. Even if an after-treatment system helps to reduce emissions, quite amount of particulate matters (PM) reduction is still necessary since a diesel particulate filter (DPF) system is supposed to be excluded in Tier4 final diesel engine. The objective of this research is to see if the base engine has a feasibility to meet Tier4 final emission regulations by a change of piston bowl geometry without DPF. Quite amount of PM can be reduced by piston bowl geometry because piston bowl geometry is a very important part that enhances air and fuel mixing process that help the combustion process.

As presented in the previous study [1], a 2.4L ULPC(Ultra Low PM Combustion) diesel engine was achieved through optimal matching with piston bowl geometry and nozzle spray angle that significantly reduce the amount of engine out soot generated in the combustion. This engine complies with US Tier 4 Final regulation without DPF (only DOC) which was developed for off-road applications such as skid-loader, forklift and construction equipment. Improvement in fuel consumption of diesel engine for off-road applications and construction equipment which are operating continuously for a long time at high load conditions will be very important for reducing the operating costs. This paper explains a detailed review of improvement BSFC of 2.4L ULPC diesel engine by optimizing the combustion system with swirl ratio, nozzle flow rate and piston bowl geometry while maintaining non-DPF solution.

A 2.4L commercial diesel engine was developed for light-duty commercial and off-road applications such as skid-loader, forklift and construction equipments. This engine complies with US Tier 4-final regulation, without PM after-treatment device by virtue of improved combustion strategy which is named as ULPC (Ultra-Low Particulate Combustion). This paper explains how ULPC works to reduce particulate matter (PM) based on the optimization of combustion system - piston bowl and nozzle specification. A baseline, re-entrant shape piston bowl, is useful to improve mixing of fuel and air in the main combustion chamber due to squish jet flow, especially in high-speed diesel engines. However, operating speed of commercial engines is almost half slower than that of passenger car engines and the merits by squish flow become deteriorated.

Premixed compression ignition (PCI) combustion was implemented using advanced injection strategy and exhaust gas recirculation in a direct-injection single-cylinder diesel engine. The injection timing swept experiment using a baseline injector, which had an injection angle of 146° and 8 nozzle holes, obtained three types of combustion regime: conventional diesel combustion for an injection timing of 10° CA (crank angle) BTDC (before top dead center), PCI combustion for an injection timing of 40° CA BTDC and homogeneous charge compression ignition (HCCI) combustion for an injection timing of 80° CA BTDC. PCI combustion can be verified by burn duration analysis. The burn duration, which was defined as the period from 10% to 90% of the accumulated heat release, was very short in PCI combustion but not in the others. PCI combustion with an injection timing of 40° CA BTDC was achieved in a range of an exhaust gas recirculation (EGR) rate from 0% to around 40%.

Two-dimensional planar imaging and one-dimensional, spectrally-resolved line-imaging of laser-induced fluorescence from CO and UHC are performed to help identify the sources of these emissions in a light-duty diesel engine operating in a partially-premixed compression ignition combustion regime. Cycle-averaged measurements are made in the clearance volume above the piston crown at a 3 bar IMEP, 1500 rpm baseline operating condition. Sweeps of injection timing, load, and O2 concentration are performed to examine the impact of these parameters on the in-cylinder spatial distributions of CO and UHC. At the baseline operating condition, the main contributions to UHC from the clearance volume stem from regions near the cylinder centerline and near the cylinder wall, where UHC likely emanates from the top ring-land crevice. Broadly distributed CO within the squish volume dominates over CO observed near the cylinder centerline.

A detailed comparison of cylinder pressure derived combustion performance and engine-out emissions is made between an all-metal single-cylinder light-duty diesel engine and a geometrically equivalent engine designed for optical accessibility. The metal and optically accessible single-cylinder engines have the same nominal geometry, including cylinder head, piston bowl shape and valve cutouts, bore, stroke, valve lift profiles, and fuel injection system. The bulk gas thermodynamic state near TDC and load of the two engines are closely matched by adjusting the optical engine intake mass flow and composition, intake temperature, and fueling rate for a highly dilute, low temperature combustion (LTC) operating condition with an intake O2 concentration of 9%. Subsequent start of injection (SOI) sweeps compare the emissions trends of UHC, CO, NOx, and soot, as well as ignition delay and fuel consumption.

UEGI(Unburned Exhaust Gas Ignition) is expected to help faster warm-up of a close-coupled catalytic converter (CCC) by igniting the unburned exhaust mixture using two glow plugs installed upstream of the catalyst. In this study, a control module and an algorithm for the UEGI technology was developed. In addition, a hydrocarbon adsorber was tested with the UEGI system for more effective reduction of HC emission during the cold start. The control module changes I/O signals of the ECU, to control ignition on/off, glow plug on/off, and A/F ratios during cold start. Because the system is designed to be applicable to conventional vehicles, its repeatability, stability, and precision of control were tested and analyzed on an engine test bench and vehicle test. Experimental results show that the CCC reaches the light-off temperature faster compared with the baseline exhaust system. Therefore HC and CO emissions are reduced significantly during the cold start.