
                                                                    Exhibit 4j

                      CLEAN DIESEL TECHNOLOGIES, INC.
                              RIGHTS OFFERING
                           ---------------------

               DTC PARTICIPANT OVERSUBSCRIPTION EXERCISE FORM
                           ---------------------



THIS FORM IS TO BE USED ONLY BY DEPOSITORY  TRUST COMPANY  PARTICIPANTS  TO
EXERCISE THE  OVERSUBSCRIPTION  PRIVILEGE IN RESPECT OF RIGHTS WITH RESPECT
TO WHICH THE BASIC  SUBSCRIPTION  PRIVILEGE  WAS EXERCISED AND DELIVERED IN
FULL THROUGH THE  FACILITIES OF THE  DEPOSITORY  TRUST  COMPANY.  ALL OTHER
EXERCISES OF  OVERSUBSCRIPTION  PRIVILEGES MUST BE EFFECTED BY THE DELIVERY
OF RIGHTS CERTIFICATES.

                           ---------------------

THE  TERMS  AND  CONDITIONS  OF THE  RIGHTS  OFFERING  ARE SET FORTH IN THE
COMPANY'S  PROSPECTUS  DATED  _______ __, 1998 (THE  "PROSPECTUS")  AND ARE
INCORPORATED  HEREIN BY REFERENCE.  COPIES OF THE  PROSPECTUS ARE AVAILABLE
UPON REQUEST FROM THE COMPANY AND THE SUBSCRIPTION AGENT.

                           ---------------------

THE RIGHTS  WILL ONLY BE GRANTED  TO,  AND MAY ONLY BE  EXERCISED  BY,
INVESTORS  RESIDING IN THE  FOLLOWING  JURISDICTIONS  WHERE THE  SECURITIES
OFFERED  HEREBY  HAVE  BEEN  REGISTERED  WITH  THE  APPROPRIATE  SECURITIES
REGULATORY  AUTHORITIES  OR WHERE AN EXEMPTION  FROM SUCH  REGISTRATION  IS
AVAILABLE:  OUTSIDE THE UNITED  STATES AND IN  COLORADO,  CONNECTICUT,  THE
DISTRICT OF COLUMBIA,  ILLINOIS,  INDIANA,  IOWA, KANSAS, MAINE,  MARYLAND,
MASSACHUSETTS,  NEVADA, NEW JERSEY, NEW YORK, NORTH CAROLINA, RHODE ISLAND,
VERMONT, VIRGINIA AND WASHINGTON. RIGHTS WILL NOT BE DISTRIBUTED TO HOLDERS
WHO RESIDE IN STATES  WHERE THE  SECURITIES  OFFERED  HEREBY  HAVE NOT BEEN
REGISTERED OR WHERE AN EXEMPTION FROM  REGISTRATION  IS NOT  AVAILABLE.  IN
ADDITION,  THE SERIES B PREFERRED STOCK MAY NOT BE TRANSFERRED TO RESIDENTS
OF  ANY  OF  THE  FOLLOWING  STATES:  ARIZONA,   FLORIDA,   GEORGIA,  OHIO,
PENNSYLVANIA OR TEXAS.

VOID UNLESS RECEIVED BY THE SUBSCRIPTION AGENT WITH PAYMENT IN FULL BY 5:00
P.M.,  NEW YORK CITY  TIME,  ON  ________  __ 1998,  UNLESS  EXTENDED  (THE
"EXPIRATION DATE").

1.   The undersigned  hereby certifies to Clean Diesel  Technologies,  Inc.
     (the  "Company")  and  ChaseMellon   Shareholder   Services,   as  the
     Subscription  Agent,  that it is a participant in The Depository Trust
     Company  ("DTC"),  that it resides outside the United States or on one
     of the  following  states:  [to  come],  and  that it has  either  (i)
     exercised  in full the Basic  Subscription  Privilege  in  respect  of
     Rights and delivered such exercised Rights to the  Subscription  Agent
     by means of  transfer  to the DTC  account of the  Subscription  Agent
     designated in the  Prospectus,  or (ii) delivered to the  Subscription
     Agent a Notice of  Guaranteed  Delivery in respect of the  exercise in
     full of the Basic  Subscription  Privilege and will deliver the Rights
     called for in such Notice of Guaranteed  Delivery to the  Subscription
     Agent by means of  transfer  to such DTC  account of the  Subscription
     Agent.

2.   The undersigned  hereby  exercises the  Oversubscription  Privilege to
     purchase,  to the  extent  available,  ________  shares  of  Series  B
     Convertible  Preferred  Stock (the  "Series B  Preferred  Stock")  and
     certifies  to  the  Company  and  the  Subscription  Agent  that  such
     Oversubscription  Privilege  is being  exercised  for the  account  or
     accounts  of persons  (which may  include  the  undersigned)  on whose
     behalf the Basic Subscription Privilege was exercised in full.

3.   The undersigned  understands that payment of the Subscription Price of
     $____ per share for each share of Series B Preferred Stock  subscribed
     for pursuant to the Oversubscription Privilege must be received by the
     Subscription  Agent at or before the  Expiration  Date and  represents
     that such  payment,  in the  aggregate  amount of  $_________.  (check
     appropriate box):

     [   ]   has  been  or is  being  delivered  to the  Subscription  Agent
             pursuant to the Notice of Guaranteed Delivery referred to above;

     [   ]   is being delivered to the Subscription Agent herewith;

                       or

     [   ]   has been delivered separately to the Subscription Agent;

and, in the case of funds not delivered  pursuant to a Notice of Guaranteed
Delivery,  is or was  delivered  in  the  manner  set  forth  below  (check
appropriate box and complete information relating thereto):

     [   ]   wire transfer of funds:
             Name of transferor institution
                                           --------------------------------
             Date of transfer
                             ----------------------------------------------
             Confirmation number (if available)
                                               ----------------------------

     [  ]    uncertified check
     [  ]    certified or cashier's check
     [  ]    money order.


                                    --------------------------------------
                                    Bank Subscription Confirmation Number

                                    --------------------------------------
                                    DTC Participant Number

                                    --------------------------------------
                                    Name of DTC Participant

                                    By:
                                       -----------------------------------
                                       Name:
                                       Title:


Date: ____________ ___, 1998

PARTICIPANTS EXERCISING THE OVERSUBSCRIPTION PRIVILEGE PURSUANT HERETO MUST
SEPARATELY SUBMIT A NOMINEE HOLDER CERTIFICATION TO THE SUBSCRIPTION AGENT.
