Tech Briefs
April 2002
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Focus engine meets Euro IV emissions
Cosworth Technology helped develop the high-output Ford SVT Focus four-cylinder engine.
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The requirements to produce high specific power, a high torque across a broad engine speed range, and very low emissions levels have been seen as mutually exclusive in a conventional normally aspirated SI engine. However, Ford Motor Co. and Cosworth Technology Ltd. engineers have developed a port-injection SI engine that achieves in excess of 63 kW/L (84 hp/L), a peak torque in excess of 97 N•m/L (71 lb•ft/L), 92 N•m/L (68 lb•ft/L) between 2500 and 6500 rpm, and meets European IV for the Focus ST170 in Europe as well as North American LEV emissions levels for the SVT Focus in the U.S. The 127-kW (170-hp) 2.0-L engine is based on the standard North American Ford Zetec engine. Engineers from Ford and Cosworth discussed the details of the engine at the Advanced Powerplant Design Concepts technical session during Congress.
To achieve the required torque across the speed range, the volumetric efficiency had to be maximized at all engine speeds, which was done by fitting continuously variable inlet valve timing, a variable length intake manifold, and a tuned exhaust manifold. To meet the emissions requirements, the catalyst lightoff time was kept to a minimum by ensuring that the engine had stable combustion when run from cold with retarded spark advance. Stable combustion when cold and a high level of flow to meet performance targets were made possible by careful optimization of intake port flow and tumble characteristics and a variable valve timing strategy. The tuned exhaust manifold and catalyst location improved engine efficiency and was able to meet the emissions targets by use of the latest tri-metal coating and metal substrates. To ensure that the maximum performance was obtained from each cylinder at all times, individual knock sensing was also used.
- Linda Trego
Denso looks to CO2 future
Denso's latest advanced climate-control developments involve carbon dioxide (CO2) refrigerant, which is considered to be one of the most promising alternatives. |
Concerns over global warming in recent years has prompted a switch in many countries to car air-conditioning (A/C) systems using HFC-134a refrigerants instead of CFC-12. However, Denso Corp. and other industry companies believe there is more room for environmental improvement and are searching for an even more environmentally benign refrigerant to reduce global warming. Denso, the global leader in A/C systems with 24% of the global market, revealed at the SAE Congress details on its latest advanced climate-control developments using carbon dioxide (CO2) refrigerant, which is considered to be one of the most promising HFC-134a alternatives.
According to Denso, the global-warming potential of CO2 is about 1/1300 that of HFC-134a, so leakage from an A/C system using the refrigerant is much less of a concern. CO2 has a lower critical temperature and higher critical pressure than does HFC-134a. Therefore, in systems adopting CO2 refrigerant, the high-pressure-side temperature exceeds the critical point and results in an operating pressure 7 to 10 times greater than that of HFC-134a.
Denso's CO2 A/C system differs from a conventional HFC-134a configuration in a number of ways. Instead of a conventional condenser, a gas cooler reduces CO2 temperature upon discharge from the compressor. The CO2 is not condensed by the gas cooler because the refrigerant exceeds its critical point on the high-pressure side. Instead, an expansion valve condenses part of the refrigerant as a result of adiabatic expansion. An inner heat exchanger between the gas cooler and main heat exchanger further cools the refrigerant by exchanging heat with refrigerant flowing on the low-pressure side of the system. The inner heat exchanger also increases cooling performance. The accumulator is eliminated on the low-pressure side since pressure on the high side is 10 MPa (1450 psi) or greater—much higher than that of the conventional system. Since the accumulator is integrated with the internal heat exchanger and expansion valve, the system is simplified and easier to install in the vehicle.
Denso and Toyota developed a CO2 A/C and heat-pump system to provide cabin cooling and heating for Toyota's FCHV-4 fuel-cell vehicle.
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Taking the concept a little further, Denso has also developed with Toyota Motor Corp. a CO2 A/C system with heat-pumping capabilities to provide cabin heat in Toyota's FCHV-4 fuel-cell hybrid vehicle (see figure), which cannot rely on waste heat from an IC engine for this capability. The system switches from heating to cooling mode via two bypass valves. Refrigerant circulates in the system much in the same way it does in the A/C-only CO2 system. For heating, bypass valve 1 closes and bypass valve 2 opens, then the air-mix dampers of the interior gas cooler open. The high-pressure and -temperature refrigerant discharged from the compressor exchanges heat with the air while flowing into the interior gas cooler. The system can perform dehumidification by closing bypass valve 2 and controlling the opening degree of expansion valve 2. The compressor for the system is driven by an electric motor, and the compressor and motor are hermetically integrated.
Given their success, Denso engineers are quick to point out that before CO2 A/C systems can enter the mass market, cost and weight must be reduced and reliability improved. The infrastructure for service and maintenance equipment as well as standardized procedures for handling CO2 systems for service and maintenance need to be developed. Because these issues are very difficult for one company to tackle, Denso intends to work with automakers, other A/C system suppliers, and governmental agencies worldwide.
- Kevin Jost
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