DOE Light Truck Clean Diesel (LTCD) Program Final Caterpillar Public Report Light Truck Clean Diesel Program
The US Department of Energy and Caterpillar entered a Cooperative Agreement to develop compression ignition engine technology suitable for the light truck/SUV market. Caterpillar, in collaboration with a suitable commercialization partner, developed a new Compression Ignition Direct Injection (CIDI) engine technology to dramatically improve the emissions and performance of light truck engines. The overall program objective was to demonstrate engine prototypes by 2004, with an order of magnitude emission reduction while meeting challenging fuel consumption goals. Program emphasis was placed on developing and incorporating cutting edge technologies that could remove the current impediments to commercialization of CIDI power sources in light truck applications. The major obstacle to commercialization is emissions regulations with secondary concerns of driveability and NVH (noise, vibration and harshness). The target emissions levels were 0.05 g/mile NOx and 0.01 g/mile PM to be compliant with the EPA Tier 2 fleet average requirements of 0.07 g/mile and the CARB LEV 2 of 0.05 g/mile for NOx, both have a PM requirement of 0.01 g/mile. The program team developed a combustion process that fundamentally shifted the classic NOx vs. PM behavior of CIDI engines. The NOx vs. PM shift was accomplished with a form of Homogeneous Charge Compression Ignition (HCCI). The HCCI concept centers on appropriate mixing of air and fuel in the compression process and controlling the inception and rate of combustion through various means such as variable valve timing, inlet charge temperature and pressure control. Caterpillar has adapted an existing Caterpillar design of a single injector that: (1) creates the appropriate fuel and air mixture for HCCI, (2) is capable of a more conventional injection to overcome the low power density problems of current HCCI implementations, (3) provides a mixed mode where both the HCCI and conventional combustion are functioning in the same combustion cycle. Figure 1 illustrates the mixed mode injection system. Under the LTCD program Caterpillar developed a mixed mode injector for a multi-cylinder engine system. The mixed mode injection system represents a critical enabling technology for the implementation of HCCI. In addition, Caterpillar implemented variable valve system technology and air system technology on the multi-cylinder engine platform. The valve and air system technology were critical to system control. Caterpillar developed the combustion system to achieve a 93% reduction in NOx emissions. The resulting NOx emissions were 0.12 gm/mile NOx. The demonstrated emissions level meets the stringent Tier 2 Bin 8 requirement without NOx aftertreatment! However, combustion development alone was not adequate to meet the program goal of 0.05gm/mile NOx. To meet the program goals, an additional 60% NOx reduction technology will be required. Caterpillar evaluated a number of NOx reduction technologies to quantify and understand the NOx reduction potential and system performance implications. The NOx adsorber was the most attractive NOx aftertreatment option based on fuel consumption and NOx reduction potential. In spite of the breakthrough technology development conducted under the LTCD program there remains many significant challenges associated with the technology configuration. For HCCI, additional effort is needed to develop a robust control strategy, reduce the hydrocarbon emissions at light load condition, and develop a more production viable fuel system. Furthermore, the NOx adsorber suffers from cost, packaging, and durability challenges that must be addressed.
- Research Organization:
- Caterpillar Incorporated
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-97OR22605
- OSTI ID:
- 1020707
- Country of Publication:
- United States
- Language:
- English
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