Using NI Engine Control System to Investigate Transient Operation With Alternative Fueling and High-Efficiency Combustion Strategies

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"Using the NI ECS, we could experimentally investigate RCCI combustion over a wide amount of engine speed and load conditions with petroleum and bio-based fuels. The NI ECS helped us research RCCI combustion to a degree of precision that is unmatched by any other engine controller we could find because of its ability to command both fueling systems and engine actuators and to implement next-cycle control."

- Reed Hanson, University of Wisconsin-Madison

The Challenge:
Obtaining a research engine controller for a novel dual-fuel, low-temperature combustion engine that offers cycle-by-cycle combustion control and has the power electronics to drive high-powered direct injectors.

The Solution:
Using an NI Engine Control System (NI ECS) with built-in functions for next-cycle control, solenoid and piezoelectric direct injector drive capabilities, and openly programmable software for unencumbered control code development.

Author(s):
Reed Hanson - University of Wisconsin-Madison

The Engine Research Center at University of Wisconsin-Madison, a leading research university, has worked to improve the emissions and efficiency of internal combustion engines since the mid-1940s. Current research topics include advanced combustion modes such as low-temperature combustion (LTC).

Increasing Engine Thermal Efficiency and Lowering Emissions

Our current project objective is to investigate the steady-state and transient behavior of LTC and the resulting exhaust emissions and thermal efficiencies. LTC may be a method for reducing harmful exhaust pollutants from diesel engines and maintaining high thermal efficiency.

RCCI Combustion

There are many types of LTC, but reactivity controlled compression ignition (RCCI) is the current mode of interest. Researchers at the Engine Research Center developed RCCI, a novel, dual-fuel LTC mode. RCCI allows low NOx and PM emissions over a large engine operating space while simultaneously increasing thermal efficiency. Previous research took place at constant engine speed or load, but our current research goals are to demonstrate transient operation of RCCI.

Specific Needs for RCCI

We needed a fully flexible ECU that could operate with multiple injectors in many non-standard configurations to accommodate novel combustion modes, such as RCCI, in a research engine test cell. Past research applications typically used stock or modified ECUs, but we found these to be unacceptable for this project. RCCI is a dual-fuel combustion strategy, so we needed to add gasoline port fuel injectors (PFI) to a standard common rail diesel engine.

Additionally, since the test engine is a production-based, multi-cylinder engine, we also needed to control a wide range of temperature and pressure sensors. No other commercially available software can operate a multi-cylinder engine and control the high-current, solenoid injectors of a modern common rail diesel engine. Since LTC and RCCI combustion strategies can be more unstable than conventional combustion strategies, we needed to control combustion phasing on a cycle-by-cycle basis, which was another limitation of current commercial software.

Engine Setup

We performed the experiments on a 1.9 liter diesel engine equipped with a variable geometry turbine, cooled exhaust gas recirculation (EGR), and variable swirl port design. Figure 1 shows detailed specifications. We used all standard production hardware with the exception of the intercooler, ECU, and the addition of a PFI fuel system. Figure 2 shows the modified intake manifold.

Engine Type

Euro 4 Diesel

Bore

82 mm

Stroke

90.4 mm

Displacement

1.9 liters

Cylinder Configuration

Inline 4

4 valves per cylinder

Swirl Ratio

Variable (2.2 to 5.6)

Compression Ratio

17.5

Turbocharger

VGT

EGR

Hybrid High/Low Pressure, Cooled

Common Rail Injectors

148° Included Angle

7 holes,

440 flow number.

Port Fuel Injectors

2.27 g/s steady flow

400 kPa fuel pressure

Figure 1. Engine Specifications

Figure 2. Modified Intake Manifold for the Additional PFI Injectors

Figure 3. Schematic Overview of the 1.9 Liter Multi-cylinder Engine

NI Engine Control System

To use RCCI operation, we replaced the OEM ECU with an NI ECS. We made this change to provide full access to all engine actuators and to control the additional PFI injectors so the engine could operate in RCCI mode. Unlike most production ECUs, the NI ECS provides real-time access and modification to all engine maps and other control parameters.

The NI ECS features a PXI-based controller, which offers full-authority control over injection timing(s) and pressure, EGR valve opening, VGT position, and other parameters that need to be adjusted to apply different combustion or control strategies. We recorded these parameters, as well as other command setpoints and measured values used by the ECU, once per crankshaft revolution to provide an overview of the control system state and supplement the data provided by other external instrumentation. We recorded additional lab parameters with data acquisition based on the NI SCXI system.

Results

Using the NI ECS, we could experimentally investigate RCCI combustion over a wide amount of engine speed and load conditions with petroleum and bio-based fuels. The NI ECS helped us research RCCI combustion to a degree of precision that is unmatched by any other engine controller we could find because of its ability to command both fueling systems and engine actuators and to implement next-cycle control.

Additionally, the next-cycle control capabilities of the NI ECS offered even more precise control over the combustion process during non-ideal conditions such as engine warm up and during changing speed and load conditions. We could even switch combustion modes in real time between diesel and RCCI.

The benefits of the NI ECS helped us show that engine thermal efficiency increased by up to 15 percent and harmful emissions of NOx and PM went down by more than 90 percent on average for most operating conditions.

Future Applications

We had such success using NI software in the engine test cell that we are developing a similar PXI-based controller to use in a series hybrid vehicle with RCCI combustion. The laboratory-based NI ECS with next-cycle control will help us implement RCCI combustion from the laboratory into the vehicle faster and more easily.

Author Information:
Reed Hanson
University of Wisconsin-Madison

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